GlobalCONTACT - 03/2021

ISSN:1386 0194

3

2021 (88)

Technology • Understanding the visual impact of the Stiles-Crawford effect • The importance of poroelasticity in soft contact lenses

Fitting Background • Context in contacts

Modern modalities require boundless imagination and limitless capabilities. Designed to support the requirements of scleral and ortho-k lens designs, Optimum Infinite’s unique properties offer you the opportunity to push the boundaries of speciality lens design.

Special Topic

optimum-infinite.com

• New challenges in ­ intra-ocular lens metrology

Interview • Lynette Johns Hyper Dk

Tailored Modulus

Inherently Wettable

Eyepress Fachmedien GmbH Saarner Str. 151, 45479 Mülheim a. d. Ruhr

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LETTER FROM THE EDITOR

Sustainability – not trivial but not impossible either!

The major issues of these times continue to be the corona crisis,

and recycling infrastructures in countries where there is no

the difficulties around global trade and production against a

functioning circular economy.

background of sustainability. The optical and contact lens

Bausch + Lomb has also continued to expand its sustainability

industries are affected differently.

efforts. The company currently reports to recycle more than 41 million contact lens, eye and lens care materials through

Let's focus on sustainability: Environmental protection is not

collaboration with TerraCycle.

always easy. Filtering contaminated water leaves a lot of waste

Another example: Menicon has long developed a concept of

that ends up being discharged more-or-less adequately, or at

sustainability. One environmentally friendly achievement is

best recycled. Avoiding domestic air travel sometimes costs

the development of their flat pack daily disposable lens. The

companies more in employee time and money than traveling

plastics used in their manufacturing process are approximately

by train. Electric cars may save CO2, but battery cell production

99% recycled. 100% recycled plastics are used for the outer

requires a lot of energy and extraction of the raw materials

packaging.

required is associated with environmental and social problems.

The list of such environmental dilemmas is endless.

And the spectacle lens industry is also showing how this can be done in many areas. For example, the company Zeiss

Often it all comes down to choosing between the lesser of two

(Germany) claims to be CO2 neutral by 2025. Essilor is

evils: either in favor of the least harmful raw materials or the

committed to contributing to carbon neutrality, circular

comparatively more environmentally friendly process. Does this

economy, worldview, integration and ethics. Emissions from

all lead to nowhere and could we save ourselves the trouble? No!

direct operations are to be made CO2 neutral in Europe by

Experts believe that the next ten years will determine what the

2023 and in other markets by 2025.

next 10,000 years will be like for our civilization. Thus there

There are also more and more sustainable products that address

is no excuse for delay! All countermeasures, no matter how

this issue. Be it thinner semi-finished products that use less

trivial they may seem, are important because they all add up

plastic, products made from sustainable materials, state-of-

in the end.

the-art filtration systems, creative recycling options for

According to Statista, industry worldwide is responsible for

production waste and much more.

19% of all greenhouse gas emissions, and transportation for

But, even though the first step has been taken, most of the

another 25%. The worldwide mass production of spectacle

journey is still ahead of us.

lenses, frames and contact lenses does its bit.

How is your company doing in terms of sustainability? Write to me with your opinion. ■

More and more companies that produce in our industry are realizing this. In a recent press release, CooperVision, for

SILKE SAGE

example, announced that it would produce its approx. 1 billion

Editor-In-Chief

disposable lenses per day (!) in a plastic-neutral way in

silke@global-cl.com

cooperation with Plastic Bank. This means that for every gram of contact lens and blister produced, the same amount of ocean-bound plastic waste is collected.Plastic Bank aims to reduce plastic waste in the world's oceans by building collection

GlobalCONTACT 3-21

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ULTRA-PRECISE AND ECONOMICAL MANUFACTURING OF CONTACT LENSES AND IOL

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Both machines can be easily integrated with an optional automation system.

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25.06.2020 17:38:13 27.10.21 15:26

CONTENT

ISSN:1386 0194

LETTER FROM THE EDITOR 3

Sustainability – not trivial but not impossible either!

Silke Sage

3

INTERNATIONAL NEWS

2021 (88)

6

Technology • Understanding the visual impact of the Stiles-Crawford Effect • The importance of poroelasticity in soft contact lenses

Fitting Background • Context in contacts

10 All about research

Modern modalities require boundless imagination and limitless capabilities. Designed to support the requirements of scleral and ortho-k lens designs, Optimum Infinite’s unique properties offer you the opportunity to push the boundaries of speciality lens design.

Special Topic

14 All about products

optimum-infinite.com

• New challenges in intra-ocular lens metrology

TECHNOLOGY

Interview • Lynette Johns Hyper Dk

Tailored Modulus

All about you & event dates

Inherently Wettable

16 The importance of poroelasticity in soft contact lenses – pt. 2 Alina Kinder

22 Understanding the visual impact of the Stiles-Crawford effect

Eyepress Fachmedien GmbH Saarner Str. 151, 45479 Mülheim a. d. Ruhr

NOW AVAILABLE AT YOUR APP STORE

Brian Vohnsen

INDEX TO ADVERTISERS Title: Contamac, www.contamac.com Inside front cover: Bausch + Lomb Inc., www.bausch.com Page 4: Schneider GmbH & Co. KG, www.schneider-om.com Page 7: REM Vision Tech, www.remvt.com Page 9: OPTOCRAFT GmbH, www.optocraft.com Page 13: K & Y Diamond Ltd, www.kydiamond.ca Page 15: Optimec Systems Ltd., www.optimecsystems.com Page 19: LAMBDA-X S.A., www.lambda-x.com Page 21: Schneider GmbH & Co. KG, www.schneider-om.com Page 25: Larsen Equipment Design Inc., www.larsenequipment.com Page 35: AMETEK Precitech, Inc., www.precitech.com Inside back cover: Efclin, www.efclin.com Outside back cover: DAC International, Inc., www.dac-intl.com

INTERVIEW 26 Interview with Lynette Johns – Drug delivery in scleral lens wear Silke Sage

FITTING BACKGROUND 30 Context in contacts Eef van der Worp

33 Imaging techniques – case study Marie Kahlert

MANUFACTURING 34 Blocking scleral lenses Erik Larsen

SPECIAL TOPIC 36 New challenges in intra-ocular lens metrology Luc Joannes

HISTORY 40 About the use of the “gel”-contact lens Hans-Walter Roth

NAMES TO NOTE Joannes, Luc

36

Johns, Lynette

26

Kahlert, Marie

33

Kinder, Alina

16

Larsen, Erik

34

Roth, Hans-Walter

40

Vohnsen, Brian

22

van der Worp, Eef 30, 42 GlobalCONTACT 3-21

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COLUMN 42 Under pressure Eef van der Worp

NEWS 44 Yellow Pages 5

19.11.21 15:25

INTERNATIONAL NEWS

All about you Ten rules for the safe use of contact lenses endorsed by TFOS

The rules have also been summarized in the educational video "Healthy

The national campaign "Healthy Eyes Are in Your Hands", an awareness

indications of correct behavior. This video involves washing and drying

project dedicated to contact lenses and their safe use, promoted by the

your hands before handling contact lenses, never letting the lenses come

Tear Film & Ocular Surface Society TFOS and supported by ASSOTTICA

into contact with water, not sleeping with contact lenses, and disinfecting

(the Italian Contact Lens Association), promotes ten rules of correct

lenses in a new solution after each use. If you wear disposable daily lenses,

hygiene and management of contact lenses.

it is important to throw them away after taking them off and not reuse them,

Eyes Are in Your Hands" in which children are the ones giving adults the

then follow the manufacturer's instructions and the specialist's instructions.

The video campaign is available on the web: https://youtu.be/VdscomrqFsw and has already reached tens of thousands of views.

"Contact lenses have a long history, and the materials with which they are made have evolved enormously over the years, thanks to intense scientific research. Today, new synthesis technologies have led to materials compatible with the ocular surface, reaching high standards of safety and comfort," emphasized Prof. Piera Versura, Head of the Ocular Surface Analysis and Translational Research Laboratory, Alma Mater Studiorum University of Bologna. “Unfortunately, we are distancing ourselves from this security mainly due to incorrect behavior. The Healthy Eyes Are in Your Hands Campaign can help you understand and remember that contact lenses are a medical device that we put in the eye, and they need care and maintenance."

CooperVision myopia control research receives Garland W. Clay Award The American Academy of Optometry has awarded the 2021 Garland

based publications noting that: “Clinical trial results provide strong

W. Clay Award to a team of researchers studying the effectiveness of

evidence that it is possible to slow ocular growth that causes worsening

CooperVision MiSight 1 day contact lenses in slowing the progression

myopia. Research into myopia control is rapidly evolving and effective

of myopia in children (aged 8-12 at the initiation of treatment). The

treatments could do more than improve vision, they may also help

prestigious award is given annually to the author(s) of the most important

lower lifelong risks for glaucoma, retinal detachments, and other

paper published in Optometry and Vision Science in the preceding

degenerative eye conditions.”

five years. The authors of the winning paper, “A 3-Year Randomized

CooperVision MiSight 1 day myopia control contact lenses are proven

Clinical Trial of MiSight Lenses for Myopia Control,” include:

to slow the progression of myopia in children aged 8-12 at the initiation

• • • • • •

Paul Chamberlain, BSc (Hons.)

of treatment. Data gleaned from these three years of research laid the

Sofia C. Peixoto-De-Matos, MSc

groundwork for FDA approval of CooperVision MiSight lenses in 2019.

Nicola S. Logan, PhD

The study, a randomized double-masked clinical trial, demonstrated

Cheryl Ngo, MBBS, MMed

the effectiveness of MiSight lenses in reducing the rate of myopia

Deborah Jones, BSc, FAAO

progression in children (aged 8-12 at the initiation of treatment) by

and Graeme Young, PhD, FAAO

59% on average over a three-year period.

The Optometry and Vision Science editorial board bestows the annual

CooperVision Director of Research Programs Paul Chamberlain, BSc

Garland W. Clay Award based upon criteria including the number of

(Hons.) said, “Our team is grateful to the Optometry and Vision Science

citations in the world scientific literature, impact of vision science,

Editorial Board and the American Academy of Optometry for

value to the practice of optometry, and relevance to the mission of the

recognizing our work. It is very satisfying to know that our research

American Academy of Optometry. After only two years since publication,

in myopia control is helping age-appropriate children and their parents

the paper about MiSight 1 day contact lenses has been cited over 70

around the world. And it is truly an honor to be associated with the

times according to Clarivate’s Web of Science and is the most cited

other pioneering papers that have previously received this distinction.”

paper in Optometry and Vision Science since 2016.

Chamberlain and team accepted the Garland W. Clay Award at the

Optometry and Vision Science Editor in Chief Michael Twa, OD, PhD,

American Academy of Optometry’s Meeting in Boston on Thursday,

FAAO stressed that his publication places a priority on quality evidence-

Nov. 4.

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INTERNATIONAL NEWS

Marcus Hughes elected to the BostonSight Board of Directors

matters, including reporting and compliance, which will support

BostonSight, a nonprofit eye healthcare organization and research

compassionate patient care and scleral lens technology globally.”

center dedicated to saving sight and improving quality of life for

Mr. Hughes received his JD from Boston College Law School

patients, have elected Mr. Marcus Hughes to their Board of Directors.

and his undergraduate degree from Middlebury College in

Mr. Hughes is Associate General Counsel at UMass Memorial

Vermont where he was a Harry S. Truman Scholar Nominee

Health Care in Worcester, MA. He serves as legal counsel to the

and part of the New England Small College

UMass Memorial Health Care (UMMHC) System and its affiliates,

Athletic Conference All-Academic Team.

with a primary focus on patient care matters. Prior to his role

He has spoken at events of the American

at UMass, Mr. Hughes was Attorney Fellow, Office of the General

and Boston Bar Associations on ethical

Counsel at Partners HealthCare in Boston, and Assistant

behav ior in t he lega l profession and

Corporation Counsel for the City of Boston. Mr. Hughes began

operational challenges in responding to

his legal career at Choate, Hall & Stewart in Boston.

COVID-19, as well as written for the

“Electing Mr. Hughes to the BostonSight Board is a tremendous

American Bar Association on COVID-19

benefit to the organization,” said Sara Yost, BostonSight

and its impact on healthcare professional

President and CEO. “He is accomplished in legal healthcare

licensure and telehealth.

Johnson & Johnson Vision receives approval in Canada for Acuvue Abiliti 1-Day Soft Therapeutic Lenses for Myopia Management

Abiliti 1-Day to be a novel soft therapeutic lens with the potential

Johnson & Johnson Vision received approval from Health

Abiliti product would provide a free comprehensive eye health

Canada for Acuvue Abiliti 1-Day Soft Therapeutic Lenses for

exam to a child in need through Sight For Kids – a joint program

Myopia Management. Abiliti 1-Day lenses are a new option of

from Johnson & Johnson Vision and the not-for-profit Lions

daily wear, single-use, disposable lenses that have the potential

Clubs International Foundation (LCIF). Sight For Kids is one

to slow the progression of myopia and are specifically designed

of the largest-known, school-based eye health programs that

for children who are seven to twelve years old at the start of

mobilizes Lions and eye care professionals to provide

treatment. “The approval from Health Canada for Acuvue

comprehensive eye health services in low-income schools

Abiliti 1-Day lenses marks another major step forward in our

around the world.

collaborative efforts with parents and eye care professionals to

Abiliti 1-Day lenses are expected to be available in select areas

reshape the future of myopia,” said Xiao-Yu Song, MD, PhD,

of Canada starting as early as this year and expanding beyond

Global Head of Research & Development, Johnson & Johnson

in 2022. Parents and eye care professionals who want more

Vision. “Our researchers and scientists specifically designed

information can visit www.seeyourabiliti.com.

BostonSight as we continue to lead in providing expert,

Marcus Hughes. Source: BostonSight

to slow the progression of myopia in children.”

The company also announced that each annual purchase of an

Advertisement www.remvt.com

Your smartest investment

Ultra precision CNC lathes for CL and IOL manufacturing

06_All About You.indd 7

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INTERNATIONAL NEWS

EFCLLIN: PFAS-registry of ECHA: five EU member states have submitted the notification for restriction of PFAS

notifier. At the end of these twelve months, the five competent authorities

On 15th July, the five REACH competent authorities – from Denmark,

open consultation via its website.

Germany, the Netherland, Norway and Sweden – notified the European

The proposal will then pass through several technical committees

Chemicals Agency (ECHA) of their intention to restrict PFAS substances

within ECHA who will give their expert opinion. The European

(Registry of Intentions).

Commission will have to decide whether to adopt or not the proposal

www.echa.europa.eu/registry-of-restriction-intentions/-/dislist/

using ECHA’s expert opinions as guidance. If they adopt it then it will

details/0b0236e18663449b

be sent to the European Parliament and the Council of the European

Submitting a notification to ECHA’s Registry of Intentions (ROI) is

Union for their approval, after which it will be published and enter

step one of the restriction process – the five competent authorities flag

into force.

a substance, allowing ECHA to get ready and industry to submit

Over the next few months, ECHA will check whether the five competent

evidence. From this moment, the five competent authorities have twelve

authorities’ notification fulfils ECHA’s requirements. If it does, then

months to prepare a restriction proposal and collect all available

they will publish the notification on the dedicated website page – the

evidence. All companies who are registered producers or users of the

Registry of Restriction Intentions – allowing the public to follow the

substance will also be notified so they can submit evidence to the

file’s progress.

will submit a restriction proposal after which ECHA will launch an

CLMA remembers and honors Jo Svochak Jo began her career in the contact lens industry alongside her husband,

Award by the CLMA, for innovation in lens design and manufacturing

Frank Svochak, Sr., a true pioneer of contact lens machining in 1976

process to the enhancement of the contact lens industry. (2006) Frank

when they founded TruForm Optics. After Frank’s passing in 1982 Jo

Svochak, Sr., received the Trailblazers Award for outstanding

assumed the role as President of TruForm Optics, (1982-2019), and her

achievement in product development to the enhancement of the contact

passion to help people see their world better was made possible through

lens industry by the CLMA.

TruForm’s countless contact lens design and machinery advancements

Jo attended her last CLMA meeting in 2018 and enjoyed the fellowship

throughout her 37 years of service to the industry.

of her life-long friends and colleagues. Jo was also able to see her

Jo went on to be a pioneer in her own right, as she was the first female

son, Jan Svochak, receive the Leonardo da Vinci Award for vision

to hold the position of President with the Contact Lens Manufacturers

in establishing the focus of the CLMA and dedication to the

Association (CLMA) from 1999 to 2000. In 2013 Jo received the

achievement of its goals. This was a momentous event for the entire

Trailblazers Award, by the CLMA, for her

Svochak family.

outstanding achievement in product

Jo had a zest for life and a personal charm

development to the enhancement of the

that drew people from all walks of life. Any

contact lens industry. Since the inception

conversation with Jo was a meaningful and

of the Trailblazers Award in 1987 Jo

memorable one. Above all of Jo’s career

remains the only female to receive the

accomplishments and her unwavering

coveted award.

dedication to the contact lens industry, her

Among Jo’s notable work at TruForm Optics,

d e e p e s t love w a s b e i n g a mot he r,

she was proud of the contributions her late

grandmother, and great grandmother. Jo

husband, Frank, and her son and current

had a special place in her heart for children,

President of TruForm, Jan Svochak, made

especially babies which always brought the

to advancing the industry forward, and she

brightest smile to her face.

took great pride in the accolades she was

Naomi “Jo” Svochak, was a compassionate

able to see them receive: (1994) Jan Svochak received the Creative Design and Process

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and loving woman, and will be missed by Naomi “Jo” Svochak 1937-2021

all those who knew her.

GlobalCONTACT 3-21

19.11.21 15:28

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WEBINARS, CONFERENCES & TRADE FAIRS 2022

(due to the corona crisis, please check via the websites whether the event takes place)

GSLS 2022 https://na.eventscloud.com/website/22990/home NCC 2022 https://contactlenscongress.com/?lang=en EFCLIN 2022 www.efclin.com ARVO 2022 www.arvo.org EAOO & ECOO General Assembly www.visiondublin2022.com ICSC 2022 www.icscmeeting.com ECLSO Congress 2022 www.eclso.eu Vision By Design www.orthokmeeting.com AAO 2022 www.aao.org IOFT 2022 International Optical Fair Tokyo

Jan 19-22

Las Vegas, NV (USA)

Mar 13-14

Eindhoven (NL)

Apr 28-30

Barcelona/ Sitges (Spain)

May 1-4

Denver, CO (USA)

May 12-15

Dublin (Ireland)

July 29-30

Fort Lauderdale, FL (USA)

Sep 2-3

Paris (France)

Sep 28 - Oct 2

Bellevue, WA (USA)

Sep 30 - Oct 3

Chicago, IL (USA)

Oct 18-20

Tokyo (JPN)

www.ioft.jp/en-gb.html

Advertisement

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18.10.21 15:28 12:40 19.11.21

INTERNATIONAL NEWS

All about research

Studies on contact lens sensors, plastic pollution and the shape of light A paper published by the journal Matter reports on the development of a new contact lens sensor system for smart contact lenses. The impact of contact lenses, specifically silicone hydrogels, as a source of plastic and microplastic pollution is the focus of a paper by a team of Arizona State University researchers.

Further studies take a look at the influence of the shape of light on our vision and present a contact lens sensor for self-monitoring of intraocular pressure.

Ultra-thin sensor for smart contact lenses

According to Dr Shiqi Guo, the first author of this study, the

In a paper published by the journal Matter, engineers from the

ultra-thin sensor layer is different from conventional smart

University of Surrey together with partners from Harvard

contact lenses in that it could be mounted onto a contact lens

University, University of Science and Technology of China,

and maintain direct contact with tears, thanks to its easy

UK National Physical Laboratory, George Washington

assembly, high detection sensitivity, good biocompatibility and

University and Zhejiang University Ningbo Research Institute

mechanical robustness. He states that it also doesn't interfere

report on how they have developed a new contact lens sensor

with either blinking or vision.

system for smart contact lenses.

Co-author Professor Sheng Zhang reports that the contact lens

The approach uses an ultrathin MoS2 transistors-based

can provide diversified signals from eyes, which could be

serpentine mesh sensor system. The integrated sensor systems

combined with advanced data analysis algorithms to provide

contain a photodetector for receiving optical information, a

personalized and accurate medical analysis for users.

glucose sensor for monitoring glucose level directly from tear

Another potential that is mentioned in the abstract is that

fluid, and a temperature sensor for diagnosing potential

the integrated contact lens sensor system and fabrication

corneal disease.

strategy could allow for easy incorporation of other functional

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INTERNATIONAL NEWS

components, such as an electrode array for electroretinography, antennas for wireless communication, and power modules for future in vivo exploration. The researchers believe that the system holds promise as next-generation soft electronics for healthcare and medical applications since the in vitro cytotoxicity tests revealed good biocompatibility.

Sources: Abstract of the paper [1], EurekAlert 2021-01-06 [2]

Plastic contact lenses in US wastewater

the US. Their survey results revealed that around 21% of users

Arizona State University researchers Charles Rolsky, Varun

flush their used lenses down the drain, a loading equivalent

Kelkar and Rolf Halden have studied the potential of disposable

to 44.000±1700 kg y−1 of lens dry mass discharged into US

contact lenses as a high-volume pollution source. They conducted

wastewater. The researchers found that biological treatment

the first study to identify contact lenses, specifically silicone

of wastewater did not result in a measurable loss of plastic

hydrogels, as a source of plastic and microplastic pollution.

mass and caused only very limited changes in the polymer

Using sales data and an online survey of lens users (n=416)

structure, as they determined by μ-Raman spectroscopy. They

alongside laboratory and field experiments at a conventional

observed that the lenses accumulated as fragments in sewage

sewage treatment plant, the researchers determined the

sludge, resulting in an estimated accumulation of 24.000 ±

environmental fate and mass inventories of contact lenses in

940 kg y−1 of microplastics destined for application on

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INTERNATIONAL NEWS

agricultural soils contained in sewage sludge. Recycling of the

during long-term, multiyear storage in septic tanks which is

contact lenses and their packaging amounted to only 0.04%

seen as interesting because an estimated 20% of households in

of the total waste volume associated with contact lens use.

the US use on-site septic systems for wastewater treatment.

In the discussion section of their paper, the researchers mention,

The team points out that hydrogel as an environmental

that the study featured some limitations in that only 66% of

pollutant through contact lenses could be almost completely

the respondents answered a survey question regarding their

avoided by properly disposing the lenses within solid waste.

age range, thereby reducing statistical power. Another factor

The paper states that at the time of the study, most products

is the unknown behavior of contact lens hydrogel polymers

in the US contained no recommendations on how to properly dispose of the lenses and their packaging materials. The teams’ research suggests that although contact lenses are a small contributor to the plastic pollution epidemic, their unique chemistry presents a threat to the environment if they are improperly disposed of. They could act similarly to microbeads or microfibers, which are also flushed down the drain.

Source: Nationwide Mass Inventory and Degradation Assessment of Plastic Contact Lenses in US Wastewater. [3]

The shape of light changes our vision

on mice. When the light hit the retina, they were able to observe

Recent studies have shown that the first stage of vision, the

an electrical voltage at the cornea, thanks to an electronic amplifier.

perception of light itself, is extremely fast. But the analysis of

Their results showed that this stage took place with the same

this decisive step was carried out on molecules in solution in

extreme speed as when the molecule is isolated.

the laboratory. Scientists from the University of Geneva

The team continued the study by varying the shape of the pulses

(UNIGE), in collaboration with Federal Polytechnic School of

over time. Changing the shape should not induce any variation

Lausanne (EPFL) and the University Hospitals of Geneva

in the response of the retina because until now it was thought

(HUG), Switzerland, reproduced the experiment on mice, in

that only the number of photons captured by the eye played a

order to observe the processing of light by a living organism

role. But this was not the case. This result could be explained

in all its complexity. This non-invasive study shows that light

with the help of computer simulations performed in the group

energy alone does not define the response of the retina. Its

of Ursula Röthlisberger from EPFL.

shape – short or long – also has an impact on the signal sent

The scientists observed that the eye did not react in the same

to the brain to form an image. This discovery, published in the

way depending on the shape of the light, even though the light

journal Science Advances, opens up a new field of research into

energy was identical. They also discovered that the eye’s reaction

vision, diagnostics and possibly new curative possibilities.

differed according to the order in which the colors were varied,

In the eye, the first stage of vision is based on a small molecule

for example as in a temporal rainbow, even though they follow

– the retinal – which, on contact with light, changes shape. When

each other extremely quickly. The retina believes that there is

the retinal alters its geometric form, it triggers a complex mechanism

more or less light depending on the shape of the light, while

that will result in a nerve impulse generated in the optic nerve.

the energy is similar, and therefore sends a stronger or weaker

This process takes some time between the moment the eye

current to the brain depending on its response. This research

perceives the light and the moment the brain decodes it. Physicists

is published in Science Advances, DOI: 10.1126/sciadv.abe1911.

looked at the retinal to see how long it took to switch its shape.

They isolated this molecule in a cuvette and subjected it to laser

Source: UNIGE [4]

pulses to test its reaction speed. To their great surprise, the molecule reacted in about 50 femtoseconds.

To study this first stage of vision in detail, the scientists called on biologists, notably Ivan Rodriguez and Pedro Herrera, professors at the UNIGE Faculties of Science and Medicine, respectively, who placed a contact lens and performed an electroretinogram 12

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Artist's view of femtosecond laser pulses arriving in an eye. Image: UNIGE Xavier Ravinet GlobalCONTACT 3-21

18.11.21 13:25

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INTERNATIONAL NEWS

Contact lens sensor for self-monitoring of intraocular pressure

The abstract reports that the sensor shows a pressure

A collaboration of researchers from different departments

polydimethylsiloxane membrane and 35.1 kHz per 1 mmHg

at Michigan State University, USA, has published a paper

change in the intraocular pressure of a canine eye. Testing

on a wireless, passive sensor that is capable of continuous

for stability showed unvaried characteristics after repeated

monitoring of the change in the curvature of cornea caused

cycles and parasitic movements. Predictable influences of

by intraocu lar pressure f luctuations. It sits inside a

temperature and humidity on the sensor response were verified

customized, planar and circular doughnut-shaped contact

experimentally and can be canceled out using real-time

lens. According to the abstract the sensor consists of a

calibration with temperature and humidity sensors to integrate

constant capacitor and a variable inductor in the form of a

with a reader device. The researchers are convinced that the

stretchable, closed-loop, serpentine wire that serves as both

design has potential clinical applications.

the sensor and the antenna.

Source: Abstract of the study [5]

responsivity of 523 kHz per 1% axial strain on a pressurized

Referenzen: [1] Guo S, Wu K, Li C, Wang H, Sun Z, Xi D, Zhang S, Ding W, Zaghloul ME, Wang C, Castro FA, Yang D, Zhao Y. Integrated contact lens sensor system based on multifunctional ultrathin MoS2 transistors. Matter. 2021 Mar 3;4(3):969-985. DOI: 10.1016/j.matt.2020.12.002. Epub 2020 Dec 30. PMID: 33398259; PMCID: PMC7773002.

[2] https://www.eurekalert.org/pub_releases/2021-01/uos-sub010621.php [3] Charles Rolsky, Varun P. Kelkar, Rolf U. Halden. Nationwide Mass Inventory and Degradation Assessment of Plastic Contact Lenses in US Wastewater. Environmental Science & Technology 2020 54 (19), 12102-12108. DOI: 10.1021/acs.est.0c03121 [4] University of Geneva (UNIGE), 28.04.2021 [5] Hossein M., Kouhani M., Wu Jiajia, Tavakoli Arman, Weber Arthur J., Li Wen. Wireless, passive strain sensor in a doughnut-shaped contact lens for continuous non-invasive self-monitoring of intraocular pressure. Lab Chip, 2020,20, 332-342. DOI: 10.1039/C9LC00735K

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TECHNOLOGY

The importance of poroelasticity in soft contact lenses Evidence of the pore space of a silicone hydrogel contact lens as transport path for pore diffusion and molecular diffusion – Part 2 Scleral lenses, hybrid lenses or Ortho-K: To ensure safe use of these types of contact lenses, the main focus is on the oxygen permeability of the plastic material of the lens. The metabolism of the cornea and the limbus should suffer as little irritation as possible. The aim of this article is to explain how this transport mechanism occurs and why it is so important. By Alina Kinder

Little is currently known about the pore space in silicone

to pores and pore spaces. With the turning process, the plastic

hydrogel contact lenses. The creation of artificial pores or pore

material is supplied in solid form, permitting the design of

space can occur in various ways. The contact lens material is

the pore space to be controlled to a certain extent. The polymer

a copolymer, produced by polymerization of a number of

manufacturing process does not lie within the sphere of

different monomers.

influence of the contact lens manufacturer but rather that of

In the production of copolymer plastics, the type of structure

the material manufacturer.

and properties of the plastic are influenced by admixtures.

In addition, it may be assumed that the first hydration, which

The type of polymerization can also be used to control the

transforms the contact lens material from a solid state into an

size of the pore space. The cooling rates [19] of the individual

amorphous or viscous structure, allows the actual pore space

manufacturing processes – whether they are produced by

to develop or be formed. [20] During this process, soft contact

shape casting, centrifugal casting, or turning – are important

lenses undergo a one-time increase in volume of approximately

for pore space design. Furthermore, changing pressure

30% which may correspond to the cavity volume.

conditions during solidification of the plastic mass can lead

Thus the cavity in soft material, resulting from pore diffusion

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TECHNOLOGY

and molecular diffusion, seems to be shaped differently from that in porous solids. It needs to be considered whether the Dk or Dk/t value really is always the same in the different hydration states. [21] When addressing this issue, it should also be clarified whether the Dk/t value needs to take account of the particular state of the aggregate.

Fig. 3: SEM (Hitachi SU3800) photos of the surface of an Efrofilcon A (silicone hydrogel material).

Small Inset: Efrofilcon A before hydration; the surface shows surface damage from the blade.

Large Inset: Efrofilcon A after the first hydration; the surface appears to have a porous surface structure.

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comfortable to wear. This allows better wetting of the contact lens and improves stability in the core.

Despite these efforts, no firm prediction can be made about the influence of the contact lens on the supply of oxygen to the cornea and wearing comfort. Not only the geometry of the cornea and the composition of the tear film but also the condition of the eyelids and the effects of the blink are important.

During blinking, when pressure or frictional forces act on the surface of the contact lens, there is a momentary change in the cavity structure and oxygen may be released. The pore space of a contact lens is not a static space. On the one hand, Fig. 4: Poly-HEMA; hydroxyethyl methacrylate polymer. A polymer that inhibits cell adhesion to growth surfaces in cultures. [22]

particles/molecules that adhere and then detach again permanently change the volume of the pore space. On the other hand, the expansion and composition of the contact lens

The type of polymerization and the composition of the individual

cavity depends very much on the surrounding conditions. Soft

components of the hydrogel or silicone-hydrogel plastic material

matter is an amorphous material that can be elastically

are decisive for the material properties, and thus also for diffusion.

deformed. During a normal blink, a pressure of 10.3 mmHg/

The production and further development of the polymer material

mm2 is exerted; during a conscious blink, pressures of about

are key challenges for the material manufacturers. The composition

51 mmHg/mm2 may be exerted [25] thus deforming the contact

of the material determines the wearing conditions of the contact

lens. Subsequently, wearing comfort appears to improve (as

lens on the eye, which are crucial for the health of the eyes.

most contact lens wearers will confirm). This material property

The manufacturing processes of the contact lenses are largely

could well be defined by the magnitude of poroelasticity.

responsible for the geometry, comfort and vision. They are

It remains to be clarified whether this blinking effectively

determined by the base curve (BC), the bevel, the size, the

"squeezes out" oxygen from the pore space. Further, it also

mobility and the surface lubricity. This calls for the expertise

needs to be investigated which, or how many residual particles

of the contact lens manufacturer.

still in the pore space are detached from the pore walls. The

Different cross-links of the polymers with different properties

blink of an eye can lead to speeds up to max. 20 cm/s. [26] The

of elasticity and deformability can be created by the various

frictional force of the eyelid triggers shearing forces which act

polymerization processes. A preferred form of the long polymer

on the surface of the contact lens.

chains is the random coil, which can change its shape dynamically.

This dynamic gives rise to the elasticity known in natural rubber.

POROELASTICITY

Structural cross-linking occurs when at least four polymers are

Against this background, further research is required to

bonded together. Due to the regular arrangement and repetition

determine whether the blink of an eyelid is capable of elastically

of the individual monomers in a polymer it can be called a lattice

altering the pore space of a silicone hydrogel contact lens to

structure, although the material exhibits amorphous properties.

such an extent that adherent molecules can be dislodged.

The definition of the Dk value should be adapted to the likely

The term poroelasticity is scarcely used in contact lens optics,

aggregate state. Furthermore, the term poroelasticity needs to be

although poroelasticity well describes the elastic behavior of

introduced into contact lens optics, because the structural cross-

a porous plastic as well as defining the stiffness of the porous

linking and the resulting elasticity cannot be adequately described

plastic. In fact, poroelasticity would be the material property

by Young's modulus (modulus of elasticity) alone. [23,24]

that can realistically describe the dynamic behavior of a soft

The formation of this cross-linking during polymerization in

contact lens during wear. Current properties used can only

the polymer material of a contact lens provides soft lenses with

define the contact lens in a static state (in the lab).

a pore space, leading to a corresponding effect on its elasticity.

The improvements in vascularization of the cornea observed

The elasticity of a contact lens is defined only by the modulus of

since the introduction of the silicone hydrogel material have

elasticity (Young's modulus). However, in the context of wearing

been attributed to the silicone content, and thus to the apparently

comfort and duration/rhythm, this one physical property is

improved circulation of oxygen. [27] It needs to be investigated

insufficient to fully describe the comfort and deformability

whether the change in rigidity of more modern materials has

during wearing. Thus, to improve wearing comfort, the industry

not also improved the durability of the contact surface. Due

is focusing on the design, surface roughness and coating of

to the extreme flexibility of the hydrogel material, very strong

contact lenses. Another way to maximize wearing comfort is to

frictional forces may arise at the contact surfaces, which in

modify the structure or composition of the contact lens. An

turn may stimulate vascularity. [28]

integrated water gradient is designed to make the lens more

In contact lens optics, the diffusion of oxygen into the tear film

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TECHNOLOGY

is based on liquid diffusion. However, what has been discussed

through the contact lens can be recorded and the time evaluated

so far suggests that the transport of oxygen through a contact

accordingly. Subsequently, the path length x can be determined

lens is more adequately described by pore or molecular diffusion

via the diffusion constant D, which is known, and the measured

than by simple diffusion processes.

time t using the Einstein-Smoluchowski equation.

Pore diffusion and molecular diffusion are processes widely

As oxygen is difficult to dye, physiological saline solution stained

used in physics and chemistry to describe the material property

with fluorescein can be used as a substitute. The diffusion of

of amorphous bodies. For porous materials, the actual diffusion

fluorescein is an obvious way of investigating diffusion.

in liquids or solids does not apply while the diffusion within

To measure fluorescein diffusion, the diffusion path of two

the pore space is more significant. Pore diffusion takes into

contact lenses was examined and compared, in order to

account the tortuosity (turns) of the cavity as well as the

demonstrate the effect of pore diffusion.

transport path, which covers a much greater distance than just the material thickness of the contact lens.

Silicone hydrogel contact lens Efrofilcon A:

Molecular diffusion does not leave out of consideration the

• Copolymer of silicone & fluorine and a lactam group N-vinyl

interaction between the pore wall and the solute, so that the adsorption processes of the solute particles are included in the diffusion process.

ILLUSTRATION OF DIFFUSION THROUGH A PORE SPACE

pyrrilidone

• 74% water content • Dk-value of 60*10-11 ml(O2)*cm2/ml*mmHg*s or a Dk-value of 45*10 -11 ml(O2)*cm2/ml*hPa*s (center thickness = 0.266 mm, Ø = 16 mm).

The pore space itself now needs to be investigated. As a possible experimental approach, colored liquid can be diffused through

Hydrogel contact lens Filcon II 3:

the pore space as detached particles. effect of pore diffusion within a contact lens. The existence of

• Copolymer of MMA and a lactam group N-vinyl-pyrrilidone • 75% water content • Dk-value of 43*10-11 ml(O2)*cm2/ml*mmHg*s or a Dk-value

cavities in a silicone hydrogel contact lens can be demonstrated

of 32*10 -11 ml(O2)*cm2/ml*hPa*s (center thickness =

by studying the diffusion over time (via video). On the basis

0.225 mm, Ø = 16 mm).

This method of liquid staining can be used to demonstrate the

of the known diffusion coefficient and the measured time, the Einstein-Smoluchowski equation (1) is used to determine the

These contact lenses were not coated and differ merely in their

transport distance, which may be longer than the known center

base material which in one case was a silicone material and in

thickness of the contact lens.

the other a MMA-VP material.

D = <x>2/2t [m2/s] (1)

To prove that systematic errors can be excluded, a reference group consisting of two very similar hydrogel contact lenses

The path taken by the oxygen (dissolved in the tear film)

was created.

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TECHNOLOGY

The reference group consisted of:

This table clearly shows that the resulting diffusion coefficient Derm – determined over time – appears to be of an order of

Hydrogel contact lens Hioxifilcon B:

magnitude less than the diffusion coefficient D of fluorescein

• Terpolymer of glyceryl methacrylate • 49% water content • Dk-value of 15.8*10 -11 ml(O2)*cm2/ml*mmHg*s or a Dk-

dissolved in physiological saline would suggest.

Assuming f luorescein diffusion is conclusive, the pore diffusion in the contact lens made of the silicone hydrogel

value of 11.9*10 ml(O2)*cm2/ml*hPa*s (center thickness

material is about six times higher than expected; in the

= 0.235 mm, Ø = 16 mm).

reference lens it is about ten times higher. Due to its larger

-11

pore space, the silicone-hydrogel contact lens allows faster Hydrogel Acofilcon B:

diffusion than the hydrogel material. In the reference group,

• Terpolymer of glyceryl methacrylate • 49% water content • Dk-value of 15.8*10 -11 ml(O2)*cm2/ml*mmHg*s or a Dk-

the diffusion coefficients found were much smaller, so that

value of 11.9*10 -11 ml(O2)*cm2/ml*hPa*s (center thickness

As far as is known, Fluorescein diffusion as discussed here

= 0.225 mm, Ø = 16 mm).

has never been used to investigate the mode of diffusion

the effect of pore diffusion was even up to 50-times greater than anticipated.

through soft contact lens materials. Thus the aim here is to These contact lenses, too, were uncoated and differed only in

demonstrate the existence, effects and magnitude of pore

the base material. The Dk value and water content were the same.

spaces in contact lenses.

The effect of the pore space x PD can be determined based on the specified center thickness x and the actually measured diffusion path x erm.

Contact lens Efrofilcon A Filcon II 3 Hioxifilcon B Acofilcon B

Center thickness of contact lens x [mm] 0,266 0,225 0,235 0,225

CONCLUSION Based on the results, when considering diffusion through a contact lens the concepts of porosity and tortuosity need to

Diffusion path xerm = √(D*2t)[mm]

Effect of the pore space x PD = xerm /x

be taken into account in order to get closer to a more realistic

0,67 0,73 1,61 1,65

2,52 3,24 6,85 7,33

of diffusion in a liquid on its own is not able to describe the

understanding of diffusion. It is now evident that the concept complex process of particle transport.

Two different diffusion processes take place in the two different soft contact lens materials: In the hydrogel contact lens material,

Tab. 2: Influence of the pore space based on the increased diffusion path measured (for given diffusion coefficients).

diffusion takes places through the aqueous phase, while in the

Instead of the assumed diffusion paths corresponding to the center

diffusion and molecular diffusion that is the driving force

thickness of the contact lenses, 2.52- to 7.33-fold longer transport

behind oxygen diffusion.

paths were measured. The Efrofilcon A lens had a shorter path

With diffusion through the water phase in the hydrogel contact

than the Filcon II 3 reference lens, due to the composition of the

lens material, Brownian motion describes the diffusion process,

copolymer material and the resulting different pore space.

allowing oxygen to diffuse through the contact lens. Random

The control group with the same two hydrogel contact lenses

fluctuations of the water molecules are responsible for oxygen

also showed a transport path significantly longer than the

flow. The amount of diffusion is temperature dependent.

actual center thickness of the two contact lenses. The diffusion

With the manufacturing process of hydration, the contact lens

paths determined for the two contact lenses Hioxifilcon B and

material undergoes expansion. During blinking, pressure or

Acofilcon B of 1.61 mm and 1.65 mm respectively were very

frictional forces are exerted on the surface of the contact lens.

similar due to their similar material composition.

This causes a brief change in the material structure, enabling

When the diffusion constants D and Derm are compared to each

oxygen to be pumped clear.

other, this results in the effect of pore diffusion EPD.

Poroelasticity can adequately explain this "oxygen pumping"

Contact lens Efrofilcon A Filcon II 3 Hioxifilcon B Acofilcon B

Diffusion coefficient of fluorescein D [m²/s] 0,42*10 -9 0,42*10 -9 0,42*10 -9 0,42*10 -9

Diffusion coefficient determined from time Derm = x 2/2t [m²/s] 6,71*10 -11 4,01*10 -11 8,93*10 -12 7,77*10 -12

Effect of pore diffusion EPD = D/Derm 6,26 10,48 47,01 54,04

Tab. 3: Effect of pore diffusion EPD, when the specified diffusion coefficient D is compared to the diffusion coefficient Derm measured (for a given center thickness).

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16_Poroelastizitaet_Teil2.indd 20

silicone-hydrogel contact lens it is the interplay between pore

process and should thus be included in the description of the wearing comfort of a contact lens on the eye.

When considering diffusion in liquids, the viscosity of the solvent plays a role. The equation below refers to the viscosity η of the solvent and not the viscosity of the contact lens material. An increase in viscosity due to particles in the tear film leads to a slowdown of diffusion.

The slowdown is not affected by the viscosity of the contact lens material itself.

GlobalCONTACT 2-21

19.11.21 15:37

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(2)

k B = Boltzmann constant (1.380649 x 10-23 J/K) T = Temperature η = Viscosity

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R0 = Hydrodynamic radius

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In the fluorescein diffusion above, the fluorescein dissolved in the reference group needed a much longer diffusion time than expected. Here diffusion occurs through the water content in the hydrogel material. The amount of oxygen diffusion via the pore spaces in the hydrogel material still requires further investigation.

Two diffusion processes play a major role in silicone hydrogel materials. One of these is pore diffusion, where the solvent diffuses through the pore space. The other is molecular diffusion, which takes account of the adsorption and capillary

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action of the solution in the pore space. The adsorption of solute particles in the phase or boundary layer of the pore walls changes the extent and nature of the pore space. This process is recurrent and thus does not represent a steady state.

The capillary action within the pore space leads to different rates of diffusion which in turn affect the diffusion time.

Pore diffusion can well represent the processes of diffusion in silicone hydrogel contact lenses. The interaction of pore diffusion through the cavity, and molecular diffusion which describes the diffusion rate through the shape of the cavity with the capillary action in the pore space, can be described by the material properties porosity and tortuosity. In addition, a more realistic insight into the amorphous nature of the polymeric contact lens material is achieved through consideration of the poroelasticity. The deformability of the material and the related development of forces such as suction and pumping forces in this connection should no longer be ignored. n This is part 2 of this article. Read part 1 in GlobalCONTACT 2021_02 and in our app.

More information on using the GlobalCONTACT app on page 46 References are available on request from the editorial office or are listed in the GlobalCONTACT app.

Alina Kinder (EurOptom, Master of Science (Klin. Optometr y)) is a lecturer at the Professional School for Optometr y in Cologne (HFAK). She also works as an examiner on the examiner board of ECOO diploma and optometrist (ZVA/ HWK).

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TECHNOLOGY

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Understanding the visual impact of the Stiles-Crawford effect The Stiles-Crawford effect (SCE) is a classic of visual optics that remains poorly understood. Discovered

by Walter Stanley Stiles and Brian Hewson Crawford in 1932, it is a directional optical effect related to the very elongated shape of photoreceptors. The effect is only observed in photopic conditions and thus it is exclusively a cone photoreceptor effect. It is commonly analyzed for a single pupil point at a time in Maxwellian view corresponding to a single angle of incidence onto the retina. This differs markedly from normal vision through the entire eye pupil.

By Brian Vohnsen

The SCE is normally represented as a pupil

WHAT CAUSES IT?

apodization. Yet, as it originates in the

Although clearly of retinal origin, the mechanism causing

optics of the retina itself, this approach

the Stiles-Crawford effect remains elusive. Photoreceptors

is invalid, and the SCE provides a much

are believed to act as biological waveguides due to an elevated

stronger apodization than predicted

refractive index. Yet, vision is only triggered when light is

with Maxwellian view. This has direct

absorbed in the outer segments where visual pigments are

implications for vision and refractive

stacked and gradually renewed within an approximately

optics of the anterior eye. In this

two week cycle. Excess light is absorbed by the dark retinal

contribution, the optics of the SCE

pigment epithelium layer beyond the photoreceptors. That

is described with emphasis on the

waveguiding is the principal cause of the Stiles-Crawford

fact that photoreceptors themselves

effect is challenged for a number of reasons: (1) foveal cones

are active optical elements that

that are directional have a similar geometry to that of

impact vision on par with the optics

peripheral rods that lack directionality, (2) waveguiding

of the anterior eye.

does not describe what happens with the nonguided light,

WHAT IS THE STILES-­ CRAWFORD EFFECT?

(3) the short length of outer segments allowing only a single or few ref lections that may not build up modes effectively, (4) foveal cones are very densely packed very unlike those

Vision is highly sensitive to the angle

of individual optical fibers, and most importantly (5)

of incidence onto the retina. This is due

waveguided oblique light would have a larger optical path

to t he elongate d s t r uc t u re of t he photoreceptor cells where visual pigment is distributed in densely packed layers within the outer segments of each cell. The common assumption is that they act like optical fibers by guiding light from the inner to the outer segment of each cell. Yet, there are indications that lensing may also be in play in the high refractive index mitochondria that are densely packed in the ellipsoid between the inner and outer photoreceptor segments. The sensitivity to acceptance angle is described by a characteristic Stiles-Crawford function that resembles a Gaussian distribution in the pupil plane. The peak of the function is because photoreceptors point towards a common point near the pupil center whereas the width of the distribution describes the angular sensitivity of the photoreceptors. Thus, if a single ray of light is incident at a pupil eccentricity of 2.5 mm it will dampen the visual response by 50% and at 3.5 mm eccentricity by 75%.

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Left: The Stiles-Crawford function of the first kind (SCE-I) is usually expressed by a Gaussian pupil apodization with a characteristic directionality parameter of approximately rho = 0.05/mm2 at the fovea. It expressed the angular acceptance curve for the photoreceptors when measured with Maxwellian light at the pupil.

Right: It is common practice to add the SCE-I function point-by-point across the pupil when analyzing its effect for the natural pupil size. Yet, this approach is flawed and severely underestimates its combined effect at the retinal plane. The effective truncation with a natural pupil is nearly an order of magnitude higher than with Maxwellian light.

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Left: Light traverses stacked layers of visual pigments in the outer segments. The total absorption is proportional to the volumetric overlap between the light and the outer segments. For oblique light some light will leak into adjacent outer segments that will absorb the light according to the cone type.

Right: Cones are either isolated or grouped in small patches within the photoreceptor mosaic, whereas rods are grouped in larger patches with highly similar rods. The larger the patch of identical receptors, the smaller is the effective directionality. The plots show calculated SCE-I visibility curves for individual to larger and larger patches of identical outer segments in a hexagonal photoreceptor array. For rods the SCE-I directionality is practically absent.

trefoil) Zernike aberration orders as only the former has a wavefront slope in the retinal plane. Additionally, the plasticity of the retinal photoreceptors as being able to readjust to maximize light capture over a period of days suggest that they show a certain degree of phototropism like that of sunflowers.

This may help understand visual adaptation as an optical mechanism to improve vision even in cases of blur and scattering The wavefront at the pupil has an accompanying wavefront slope at the retina only for even-order Zernike aberrations. For odd-order Zernike aberrations the point-spread function is similarly degraded, but the wavefront is incident along the axes of the photoreceptors and is therefore not attenuated in the same manner by the SCE-I.

of light, and ultimately help understand what optical mechanisms trigger and drive myopia in dim light such as indoors with larger pupil sizes.

HOW DO WE TAKE IT INTO ACCOUNT? Apodization of the pupil with a Stiles-Crawford effect is in the outer segments and therefore effective visibility should

only valid on a ray-by-ray basis but not for the combined

be larger, not smaller. Thus, I have recently argued that

effect of vision through the natural pupil where its effect is

leakage of light rather than waveguiding may be the main

nearly an order of magnitude larger with a drop-off in

reason for the Stiles-Crawford effect. This agrees with other

visibility with pupil size being closer to that of a power law

reports of crosstalk between adjacent photoreceptors, but

and therefore there is a strong preference for small pupils.

also explains why there is a small hue shift for oblique light

The time is due to consider the Stiles-Crawford effect

(the Stiles-Crawford effect of the second kind) as light leaks

rightfully in the retinal plane as only then can we evaluate

into adjacent cones containing a different type of visual

its true role in vision. n

pigments (there are three cone types: long wavelength sensitive red cones, medium wavelength sensitive green cones, and a small fraction of short wavelength sensitive blue cones) whereas in the case of rods, any leakage into adjacent rods, will f latten the directionality response.

WHY DOES IT MATTER? A careful understanding of the optics of the retina and photoreceptors is vital as it is the last optical element of the eye where images projected by the anterior eye trigger a visual sensation. The Stiles-Crawford effect shows that the angle of incident onto the retina is critical for vision. It also differentiates between even (defocus, spherical) and odd (coma, astigmatism, 24

22_Vohnsen.indd 24

Brian Vohnsen, MSc, PhD, is a Fellow of Optica (Optical Society) and Associate Professor in optical physics at University College Dublin (UCD) in Ireland. He received his PhD in NanoOptics at Aalborg University in Denmark. His current research spans from advanced optical imaging techniques and adaptive optics to understanding vision with a special focus on the optics of the retina.

He lectures both optics and physics, being twice a winner of the UCD College of Science teaching award and chairs postgraduate programs in physics and the physics committee on equality, diversion and inclusion. Contact: brian.vohnsen@ucd.ie

GlobalCONTACT 3-21

19.11.21 15:41

PR-Advert

Larsen Equipment In 2004, Keith Parker and I opened Advanced Vision Technologies (AVT). At that time, the economy was going through a very bad recession and as a result, it was impossible for a new business starting up to get a loan. We immediately reached out to Erik and Pam at Larsen Equipment to get refurbished equipment to use in our Laboratory. As AVT’s business grew, we invested in many different pieces of new equipment from Larsen Equipment and this helped us grow into one of the Premiere Labs in the United States. Our success is due in part to Erik and his Team with their state-of-the-art equipment and maintenance of their products. AVT is forever grateful for Larsen Equipment’s support of AVT. It is great to know AVT is working with Industry leaders with the Larsen Equipment and their Team!

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PR_Larsen.indd 25

969 S. Kipling Parkway, Lakewood, CO 80226 Phone: 303-384-1111 888-393-5374 Fax: 303-384-1124 www.AVTLENS.com 25

19.11.21 15:45

FITTING BACKGROUND

Drug delivery in scleral lens wear Interview with Dr Lynette Johns, Harvard Medical School Department of Ophthalmology Drug delivery in scleral lens wear is still a bit uncharted territory, although talk about this and pioneering work in the field date back at least a few decades. The areas of potential application could be prevention against corneal infection in case of corneal defects, and particularly in case of persistent epithelial defect healing. These defects can be very difficult to re-epithelialize, and it is important to use prophylactic antibiotics, to prevent corneal infection in these vulnerable eyes.

Another area of potential application could be the use of medication that prevents neovasculasation in the cornea. These drugs can prevent new blood vessel growth in the cornea. Other areas such as glaucoma medication application are still under investigation. Here, like in general scleral lens fitting, it is the balance between the benefits and the costs (including risks etc.) that need to be considered. Here is an overview of what we know so far.

By Silke Sage GlobalCONTACT: Which drugs are generally suitable for the

Depending on the underlying condition, they can be very

administration through scleral lenses?

difficult to re-epithelialize. Using aggressive lubrication

Lynette Johns: If there is an epithelial defect on the cornea,

and bandage soft contact lenses is typically

it may be wise to have an antibiotic present to prophylactically

needed. It is important to use

prevent against a corneal infection. One of the antibiotics we

prophylactic antibiotics as

use is Moxifloxacin – that provides dual protection against

described above, to

gram-negative and gram-positive microorganisms. Moxifloxacin is a preservative-free ocular therapeutic, which makes it ideal for applying in the reservoir of a scleral lens. Preservatives of topical medications are toxic to the cornea with extended exposure times or dosing in drop form. When preservatives are used in a scleral lens, they can cause dense superficial corneal staining.

GlobalCONTACT: When are they applied?

Lynette Johns: If there is a persistent epithelial defect, then this may be particularly useful. A persistent epithelial defect is a non-infectious focal loss of corneal epithelial cells. Often, they are caused by mechanical trauma, neurotrophic corneal disease, or post-surgically.

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FITTING BACKGROUND

prevent corneal infection in these vulnerable eyes. In extreme

Moxifloxacin was used in all cases, and 17 eyes resurfaced.

longstanding cases the eyelids are sewn partially closed

There were no cases of microbial keratitis in theses 20 cases

(tarsorrhaphy) in order to heal and resurface the cornea. To

using moxifloxacin in the reservoir. 2

prevent this, scleral lenses have been used to resurface corneal

I worked with Dr. Perry Rosenthal using extended wear of scleral

epithelial defects.

lenses with prophylactic Moxifloxacin in the reservoir of the

Drug delivery using scleral lenses was first suggested in a

lens in many of these cases. It was remarkable to see how quickly

publication in 2000 by Dr. Perry Rosenthal and colleagues.[1]

and effectively this worked. The protocol for this treatment

In this retrospective study, 14 eyes with persistent epithelial

method was published by Ciralsky et al. in 2015.3

defects were treated with extended wear of scleral lenses and in some cases, there were prophylactic antibiotics placed in

GlobalCONTACT: What is the requirement for these types of scleral

the reservoir of the lens with the saline. Unfortunately, there

lens fitting and how is the drug administered?

were four cases of microbial keratitis, but eight eyes completely

Lynette Johns: Basically, a scleral lens is fit as optimally as

resurfaced. Moxifloxacin was not used in this study. Later,

possible, with the plan to have no scleral lens compression or

this same group retrospectively reviewed

impingement on the conjunctiva. The lens is filled with

20 d i f ferent c a ses w it h

preservative-free saline and one drop of moxifloxacin and applied

epithelial defects where

on the eye using the typical method for scleral lens application (head parallel to the floor). The lens is worn on an extended-wear basis for 24 hours and the eye is examined carefully the next day. The lens is removed, photos are taken for comparison, the epithelial defect is measured, and all signs of microbial keratitis are ruled out. The lens is disinfected, and the same process is repeated daily until the defect has resurfaced. In some cases, the epithelium is very fragile and can break down the first night the lens is not worn. We would have patients wear the lens an extra night with the antibiotic to allow the epithelium to “tack down”. In my experience, the majority of corneas would resurface within two weeks. If

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FITTING BACKGROUND

the healing was slow, we would manufacture two lenses for the

absorption, the patients had punctal occlusion. The drug needed

patient and train him/her on careful application and removal

to be compounded made-to-order and preservative-free – which

of the lens. When proficient we dispensed both lenses. They

is expensive. The lens was worn daily only, and patients removed

would wear them on a “12/12” schedule. Basically, they would

the lens and reapplied the drop midday for a total of two days

wear a fresh lens with the antibiotic in the morning while the

dosing in the lens. This treatment continued for three months

nighttime lens is disinfecting during the day, and then remove

and was continued based on the discretion of the corneal

that lens at bedtime and put a fresh lens in with the antibiotic

specialist.4,5 Long-term results ranging from six months to eleven

and then disinfect the daytime lens overnight.

years of 13 patients who used a course of bevacizumab in the

When epithelial defects healed, the patients would wear the

lens were reviewed and approximately 90% of eyes had a reduction

lenses daily and lubricate aggressively at night. If their lids

in corneal neovascularization and approximately 75% had an

open at night while sleeping, we would have them tape the eye

improvement in best corrected visual acuity.6

closed while they slept.

GlobalCONTACT: How do you make sure, the dosage is correct?

28

26_LynetteJohns.indd 28

GlobalCONTACT: Are there other potential fields of application?

Lynette Johns: In the previously described studies, one drop

Lynette Johns: Another medication used in the lens was topical

was placed in the reservoir with the saline solution. The

1% bevacizumab which is an anti-vascular endothelial growth

problem with drug delivery in scleral lenses is dosing. The

factor (VEGF) medication. VEGF is a prominent factor that

reservoir is different for each patient and the dilution would

promotes neovascularization – new blood vessel growth in the

also be difficult to determine. It is unknown what percentage

cornea, and this drug can slow down the progression of that

of the drug is ideal. Drug delivery with a scleral lens is a

process. It has been injected into the eye to prevent retinal

novel use of scleral lenses and is truly in its infancy.

neovascularization and also injected into the conjunctiva against

Practitioners should be cautious if delivering topical

corneal blood vessel formation. It also had been used topically

medications using this technique.

to prevent corneal neovascularization. I worked with Dr. Deborah

In topical medications where drops are administered directly

Jacobs who was the first to use this medication in the lens for

to the eye, most of the ocular medication is lost within 15-30

patients who demonstrated new blood vessel growth that was

seconds after instillation.7 The tear turnover rate is approximately

potentially sight-threatening. This use of 1% bevacizumab is

16% per minute whereby all the drug disappears within ten

off-label and carries potential risks of poor wound healing,

minutes after dosing. Furthermore, the instilled drop is diluted

corneal thinning, and ulceration of the cornea. To avoid systemic

by 1/3 of the original drop.8 GlobalCONTACT 3-21

19.11.21 15:48

FITTING BACKGROUND

GlobalCONTACT: When should scleral lenses vs eye drops be used?

Again, it depends on the licensing and regulations of each

Lynette Johns: I would be very cautious considering scleral

country. Even in the United States, therapeutic licensing for

lenses for drug delivery at this time unless further research

optometrists varies from state to state.

is conducted. Risk and benefits should be clearly delineated before attempting drug delivery versus topical therapies

GlobalCONTACT: Could atropine also be administered in this way?

such as eye drops. In the presence of an epithelial defect

And if so, what would be the advantages?

that does not respond to conventional therapy, I would use

Lynette Johns: Atropine is a very potent medication with

a scleral lens to resurface the defect with moxifloxacin since

significant side effects even with topical application. This

it has been shown to be effective. Close monitoring of the

most certainly requires further study before using in a lens

patient is required and may involve daily monitoring which

on a patient.

can be difficult depending on practice scheduling. The expense of compounding drops for use in scleral lenses may

GlobalCONTACT: Are there specifications for the lens material?

be cost-prohibitive for some patients. But of course this

Lynette Johns: There are no specifications regarding lens

needs to be performed in a highly controlled, hospital setting

materials in my experience with either of these medications.

– and its use may be restricted depending on what part of

In the cases of anti-VEGF treatment, the highest Dk materials

the world and what profession you are in.

were used to enhance the oxygen permeability because of the presence of corneal neovascularization.

GlobalCONTACT: Does this cause any problems?

Lynette Johns: I think many people would like to consider using a scleral lens to deliver glaucoma medications; however, I think that’s premature at this time. I am concerned about the actual concentration of the drug in the reservoir of the lens.

Would one drop of a conventional glaucoma medication be too strong for long-term exposure? Would it be ineffective and too diluted? We just don’t know those answers. Also, the volume of the actual reservoir of a vaulted scleral lens is unknown and changes with settling. I hope that this is researched to determine and titrate the appropriate concentration in the lens of all topical medications. Once it is carefully researched, this could be an effective pressure lowering treatment especially for noncompliant patients with glaucoma. To be clear, I am not advocating its use in this capacity at this time.

GlobalCONTACT: Is the application (over the surface of the cornea and limbus) evenly distributed by the scleral lenses? Or does it not matter?

Lynette Johns: This is a great question, and something that would need further study. But the same question applies to eye drops potentially too.

GlobalCONTACT: Is the medication of the eye drops generally different from the administration via scleral lenses – is only the quantity lower?

Or is a different concentration necessary?

GlobalCONTACT: Thank you very much for this Interview!

References: [1] Rosenthal P, Cotter JM, Baum J. Treatment of persistent corneal epithelial defect with extended wear of a fluid-ventilated gas-permeable scleral contact lens. Am J Ophthalmol. 2000 Jul;130(1):33-41. doi: 10.1016/s00029394(00)00379-2. PMID: 11004257.

[2] Lim P, Ridges R, Jacobs DS, Rosenthal P. Treatment of persistent corneal epithelial defect with overnight wear of a prosthetic device for the ocular surface. Am J Ophthalmol. 2013 Dec;156(6):1095-101. doi: 10.1016/j. ajo.2013.06.006. Epub 2013 Sep 25. PMID: 24075432.

[3] Ciralsky JB, Chapman KO, Rosenblatt MI, Sood P, Fernandez AG, Lee MN, Sippel KC. Treatment of Refractory Persistent Corneal Epithelial Defects: A Standardized Approach Using Continuous Wear PROSE Therapy. Ocul Immunol Inflamm. 2015 Jun;23(3):219-24. doi: 10.3109/09273948.2014.894084.

Epub 2014 Mar 21. PMID: 24654929.

[4] Lim M, Jacobs DS, Rosenthal P, Carrasquillo KG. The Boston Ocular Surface Prosthesis as a novel drug delivery system for bevacizumab. Semin Ophthalmol.

2009 May-Jun;24(3):149-55. doi: 10.1080/08820530902802013. PMID: 19437350.

[5] Keating AM, Jacobs DS. Anti-VEGF Treatment of Corneal Neovascularization.

Ocul Surf. 2011 Oct;9(4):227-37. doi: 10.1016/s1542-0124(11)70035-0. PMID: 22023817.

[6] Yin J, Jacobs DS. Long-term outcome of using Prosthetic Replacement of Ocular Surface Ecosystem (PROSE) as a drug delivery system for bevacizumab in the treatment of corneal neovascularization. Ocul Surf. 2019 Jan;17(1):134141. doi: 10.1016/j.jtos.2018.11.008. Epub 2018 Nov 20. PMID: 30468876; PMCID: PMC6340761.

[7] Shell JW. Pharmacokinetics of topically applied ophthalmic drugs. Surv Ophthalmol. 1982 Jan-Feb;26(4):207-18. doi: 10.1016/0039-6257(82)90081[8] Maurice D, Mishima S: Ocular pharmacokinetics. in SearsML (ed): Pharmacology of the Eye. New York, Springer-Verlag,1984, pp 19–116 [9] PMID: 7041308.

Many thanks to Eef van der Worp for his comments.

Lynette Johns: Most probably it will be different, but we have no clue at this point on how much and why.

GlobalCONTACT: Is the application for non-professionals doable?

Or does the optometrist or ophthalmologist have to apply it?

Lynette Johns: Patients have been able to apply the medications independently in the lens if they were proficient at application and removal. When using topical drugs in the lens, patients must be carefully watched by optometrists or ophthalmologists.

GlobalCONTACT 3-21

26_LynetteJohns.indd 29

Dr. Lynette Johns is a research associate at Harvard medical school department of ophthalmology. She exclusively fits scleral lenses at Massachusetts Eye and Ear Infirmary. She is an author and co-editor with Melissa Barnett of the textbook: Contemporary Scleral Lenses: Theory and Application. She has published and speaks internationally on scleral and specialty contact lenses.

29

19.11.21 15:48

FITTING BACKGROUND

Let’s have a look at context within the contact lens industry.

Context most commonly refers to the environment or setting in which something (whether words or events) exists.

There may be a few context issues that are worthy of discussion, both here and at future meetings within our field. By Eef van derWorp

30

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FITTING BACKGROUND

EPONYMS

Infection. One can imagine how this could have a huge impact

The impressive British Contact Lens Association (BCLA)

on behaviour. And it does. Different terminology given for the

CLEAR papers – in which CLEAR stands for contact lens

same condition inf luenced management preferences and

evidence-based report – shine an interesting light on terms

psychological outcomes in a consistent pattern, according to

used in our field. Laura Downie from the University of

the study. Changing the terminology may be one strategy to

Melbourne in Australia is the lead author of part one of that

reduce patient preferences for aggressive management responses

series (eleven papers in all) that focuses on the anatomy and

to low-risk conditions.

physiology of the anterior eye. She composed this paper with

So, here is something to think about – from eye care practitioners

a team of experts from around the world including some

toward their patients and also from manufacturer to client,

European hotshots. Everybody who is active in the contact lens

and in everyday life on an almost constant basis, really – be

field should maybe have a look at this (the papers are open

careful what words or phrases you use in any given situation.

access from the Contact Lens & Anterior Eye website) to

It may change the outcome.

understand the landing tarmac of the lenses we so dearly love.

The first thing the committee notes is that in general, the trend

CONTACT LENS SAFETY

is to avoid eponyms where possible. An eponym is a person,

One ‘biggie’ in our field, of course, is contact lens safety. In

place, or thing after whom or which someone or something is,

many countries, there are unfortunately hefty discussions

or is believed to be, named. An example is Zeppelin (the first

between ophthalmologists and contact lens specialists on the

balloon with propellers that was directable), which is derived

safety of orthokeratology. Is the ophthalmology world right?

from the name of the German general and aeronautical pioneer

Depends on how you look at it, I suppose. If you see a number

Ferdinand von Zeppelin.

of MK (microbial keratitis) cases in a given week because of

In the cornea alone, we have several eponyms, the first being

orthokeratology I can imagine that you may wonder whether

Bowman’s layer after the English physician, anatomist, and

this is the right modality (for children particularly). So, there

ophthalmologist William Bowman (1816–1892). This layer

is work to do: we need to make our contact lens practices as

is thin but very strong. It separates the corneal epithelium

safe as possible, and there is room for improvement.

anteriorly from the stroma. The new term for this, which

Acanthamoeba infection, for instance, is almost exclusively

would directly point to its location in the cornea and,

contact lens-related and is also linked to tap water. Hence, it

to some degree, to its function, would be anterior

has been called a ‘preventable disease’. At the same time, all

limiting lamina. Don’t be surprised to see that term

practitioners in large practices with whom I’ve spoken who

appear in future papers. The same is true with

do a lot with orthokeratology report hardly any cases of

Descemet’s membrane (after the French physician

corneal infection with the modality in their database. It almost

Jean Descemet, 1732–1810). This would now

seems as though for the experts in the field who are on top

become posterior limiting lamina, as it separates

of things, the infection rate is not all that high. But every

the posterior part of the cornea (the stroma)

infection is one too many.

from the endothelial layer. There is discussion

How to deal with this, in general, when you fit a pair of

to do the same with Meibomian glands (after

contact lenses? On one hand, you don’t want to scare newbie

Heinrich Meibom, a German physician

lens wearers. Contact lenses are a safe modality; pretty

who lived from 1638–1700 and who first

much everybody is on board with that. On the other hand,

described these). There was no consensus

you don’t want to downplay things. You want to make sure

within the CLEAR team at this point to

that patients are compliant, that they follow the rules and

change this to tarsal gland, but that may

regulation, and that they understand that there is a risk of

change in the future too.

infection. A little bit of good information about these risks

“PINK EYE” Laura Downie, in her BCLA presentation on her CLEAR paper, further explores the importance of the use of terms. She refers to a nice research article by Nickel et al: “Words

seems warranted. So, it is about how you phrase things.

This is a great profession to be in, but not necessarily a simple one per se.

LET’S MOVE ON – USE MICRON!

do matter: a systematic review on how different terminology

Another term that most likely will become more relevant going

for the same condition influences management preferences”.

forward and will become the new standard in the contact lens

In this systematic review, they look at several medical conditions

field is ‘micron’. Microns of height are the new millimeters of

and how they are described. One of them happens to be from

radius in contact lens terminology. As we are moving away

the eyecare field; to describe the condition of conjunctivitis,

from central keratometry values to full corneal topography,

you could use the term Pink Eye, or you could refer to it as Eye

we are also starting to think in elevation and height. The

GlobalCONTACT 3-21

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19.11.21 15:49

FITTING BACKGROUND

appropriate term for that is micrometer (micron): which is, of

thick. To get a good perspective of things, it would probably

course, 1/1000th of a millimeter.

be better to switch to microns.

The decision on when to fit a spherical corneal lens versus

You see that in dealing with these layers and with our lenses,

a toric corneal lens can now be made based on microns of

we are talking about very small numbers. People may be

height (typically in the 30-micron range is the cut-off point).

‘thin-skinned’, as a figure of speech, when it comes to leaving

This is true, too, for spherical versus toric orthokeratology.

curves behind and/or switching from millimeters to microns.

Also, the decision on when to go from a corneal lens to

But students in schools now start to think in microns first, with

scleral lens is height dependent; studies at Pacific University

curves ‘second’. It may be time to move on.

have found that in 88% of cases, patients with less than 350 microns of corneal elevation difference along one meridian

AXL

(the one with greatest variance) had good success with a

Extending this to a new standard of care entering our field,

corneal lens. But if there is more irregularity than that, then

myopia management: trying to not make this a lengthy article,

a scleral lens could be indicated. To top it off: when fitting

myopia management is all about length. Myopia is an axial

scleral lenses, when is a toric scleral lens needed as an upgrade

length disease. So, to keep it short, when you follow change in

from a standard spherical scleral lens? We know from research

myopia development, it is all about axial length (AXL) of the

by Greg DeNaeyer et al that if a 16 mm circle is drawn onto

entire eye. Managing myopia based on subjective or objective

the scleral surface concentric to the limbus, less than 6% of

refraction is much too variant, and 0.25D steps are too coarse.

eyes have a scleral asymmetry of more than 300 microns at

At the recent ARVO meeting – the research congress in the

16 mm, which is considered ‘spherical’ by that definition.

ophthalmic field – the six-year data of a soft lens for myopia

Anything more than that may be eligible for a toric or

management (MiSight) was presented. This data showed that

asymmetrical scleral lens design.

the maximum average change in six years that can be achieved is about half a millimeter: 0.529 mm, to be precise. Why not

Scleral lenses have really opened our minds, and the road,

put this in microns? 529 microns sounds more exact and more

toward using microns; everything from the elevation on the

applicable. In the MiSight study, 0.25D change in myopia was

ocular surface, to clearance (fluid reservoir, vault) and trial

considered equal to 0.1 mm change…or shall we use 100

sets for sclerals is in the micron nomenclature. And soft contact

microns? Average growth of the eye between 10 and 13 years

lenses are presented in overall sagittal height now too (in

of age was 90 microns per year in the study, while for myopes

microns) – see my last contribution to GlobalCONTACT: ‘Mind

not receiving treatment this was 160 microns annually. But the

the Gap’.

point is, shall we use microns here (instead of 0.09 mm and

A THIN SKIN

0.16 mm, respectively, in this case)?

To follow change, this AXL measurement needs to be repeated

To put things in perspective, and circling back to the anatomy

on a regular interval (probably every six months). The changes

and physiology of the anterior eye CLEAR paper, the thickness

are subtle; there is some discussion on what normal change is,

of the cornea is 540 microns and is considerably thinner in

and it may be dependent on the amount of myopia. But in any

keratoconic eyes. The cornea is comprised of five principal

case, a parent would be more impressed if our treatment reached

layers, of which the most anterior layer (the epithelium) is

110-micron reduction in myopia progression rather than

approximately 50 microns thick. Extremely important tissue,

0.11 mm, presumably.

of course, when it comes to orthokeratology. You may want to indent or massage that epithelium to some degree, but

It is all about context. And what terms are used. n

not t he f ull t hick ness. The anterior limiting lamina (Bowman’s layer) is approximately 8 microns thick – as said, very thin but also very sturdy. The stroma is the bulk, with about 470 microns of tissue, which can swell (and thus increase) if oedema is present. Four percent swelling is considered physiological – e.g., this is the average amount of swelling that we see in the open eye upon awakening after a night of eyelid closure. The posterior limiting lamina (Descemet’s) is 3–20 microns thick; it increases in thickness with age. Finally, the endothelium is a very thin single cell layer (3–5 microns thick) that actually thins a bit with age.

The normal human tear film is only 2-5 microns thick. In millimeters, the tear film would be 0.002 to 0.005 millimeters 32

30_Eef_Context.indd 32

Eef van der Worp, BOptom, PhD, FAAO, FIACLE, FBCLA, FSLS is an educator and researcher. He received his optometry degree from the Hogeschool van Utrecht in the Netherlands (NL) and has served as a head of the contact lens department at the school for over eight years. He received his PhD from the University of Maastricht (NL) in 2008.

He is a fellow of the AAO, IACLE, BCLA and the SLS. He is currently adjunct Professor at the University of Montreal University College of Optometry (CA) and adjunct assistant Professor at Pacific University College of Optometry (Oregon, USA). He lectures extensively worldwide and is a guest lecturer at a number of Universities in the US and Europe.

GlobalCONTACT 3-21

19.11.21 15:49

FITTING BACKGROUND

Imaging techniques Photo presentation: Students present their findings

Photograph Marie Kahlert (HFAK, Cologne, Germany)

What can be seen here?

During a routine procedure, a blood vessel was noticed in the temporal region of the iris during the examination of the marginal ring network of the right eye. This runs visibly from the outer edge of the iris (at approx. 8 o'clock) in a radial pattern to the centre of the iris and lies not in, but on the iris stroma.

Imaging technique:

1

Slit lamp (Haag-Streit BQ 900, Koeniz, Switzerland), diffuse illumination, image 1 with 25x magnification and image 2 with 40x magnification.

Finding:

Normally, the blood vessels contained in the iris stroma are not visible as they are hidden by the collagen fibres.

The stroma contains the inner and the outer vascular ring, which are interconnected by small arteries. The blood vessels are responsible for supplying the iris with nutrients, transporting away metabolic products and foreign particles, and warming the aqueous humour in the anterior chamber of the eye so that it remains in motion.

The iris neovascularisation present here may possibly be the result of uveitis in the anterior segment of the eye (iritis), which can lead to rubeosis iridis.

2

Characteristics:

However, it is very likely that this is only a physiological anomaly, as the findings in relation to the medical history do not suggest a pathological change or possibly recurrent inflammation of the choroid in the iris area.

Further procedure:

No further therapy is necessary as progression of the neovascularisation is not expected due to the unchanged and persistent condition.

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MANUFACTURING

2

1 20mm 15mm 11mm

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B

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UNLESS OTHERWISE SPECIFIED:

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LARSEN EQUIPMENT DESIGN INC

DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL: 1/32 ANGULAR: 1º FIRST PLACE DECIMAL: 0.030 TWO PLACE DECIMAL: 0.010 THREE PLACE DECIMAL: 0.005 FOURTH PLACE DECIMAL: 0.001 MATERIAL FINISH REQUIRED

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1

Blocking scleral lenses Matching the tool to the back surface geometry We at Larsen Equipment Design (LED) have been providing blocking solutions to the contact lens and IOL industries for decades. In the last few years, the concept of matching the convex blocking tool (arbor, chuck, etc.) to the back surface has re-emerged. This is especially true when making scleral lenses.

By Erik Larsen

34

34_Larsen.indd 34

In recent months we have attempted to provide matched blocking

blocking compound (wax) thickness. The blocking tool

tools (arbors) to labs. We usually sell the blocking tools uncut

would have a bi-curve (lenticulated) geometry that is close

so that the lab personnel can turn the tool to fit a range of back

to the back surface geometry of the lens; only reversed. The

surface geometries. Thus, a set of five or six tools would suffice

benefit of this approach is to minimize the difference in

to span the range of the scleral designs. What has come to light

wax shrinkage due to variation in wax thickness across the

is that some of the labs are making lenses under license to

back surface.

another lab. The licensed lens design is proprietary, and the

We found (by graphics) that scleral lens designs in the 14-

licensed lab may not have access to the actual physical parameters

16 mm diameter range may not benefit from the lenticulated

of the back surface. The situation is problematic when they

blocking tool. The diameter of the base curve optic zone can

need to turn the blocking tool to approximate the back surface

be in the 11-12 mm range leaving a peripheral ring width of

geometry of the lens.

one to four millimeters. These lenses can have an edge lift of

The basic idea of matching the blocking tool to the back

a fraction of a millimeter. The lens is about as thick as the

surface geometry is to provide an approximate uniform

edge lift, so deforming the edge due to wax shrinkage is GlobalCONTACT 3-21

18.11.21 12:42

!AZ.ind

MANUFACTURING

unlikely. For example (not a real lens design): A lens with a

if this is a significant deviation from the design of the lens. To

back surface radius (BCR) of 8 mm, optical zone diameter

be clear, the PC will return to the lathe turned radius, so the

(OZD) of 11 mm, peripheral curve radius (PCR) of 11 mm,

fit as indicated by fluorescein will not be steeper. However, the

and a lens diameter of 15 mm. Here, a blocking tool with a

edge thickness may have increased which the patient may feel.

single 8 mm radius would work fine because the increased

Again, creating a blocking tool to approximate the back surface

thickness of wax at the edge is not enough to measurably pull

geometry is a good goal, but you need to temper that with the

the edge toward the arbor. The tendency of the wax shrinkage

practicality of how many arbors you need to cover the range

is to pull the edge of the lens toward the blocking tool resulting

of scleral lens designs. Lenses in the 15-17 mm diameters are

in a thicker edge than expected. In this example, the peripheral

probably OK with the single radius arbors, but larger lenses

curve width is 2 mm with an approximate edge lift of around

may benefit with an arbor with a lenticulated geometry. n

0.7 mm. If the edge thickness is on the order of 0.5 mm, it is probably strong enough to resist deformation.

So, when do you need a lenticulated blocking tool? Let’s look at a 20 mm diameter lens. Possible parameters could be: BCR of 8 mm, OZD of 12 mm, PCR 12 mm (again, not a real lens design). If we were to block this to an 8 mm single curve blocking tool, the edge lift at the 20 mm diameter would be about 2 mm.

That is a volume of wax that will shrink significantly. If the effective wax shrinkage is 5%, that is a pull of 2 mm X .05 =

Erik Larsen graduated from the University of Washington with a Mechanical Engineering degree in 1981 and started Larsen Equipment Design later that year. Erik Larsen has industry awards from CLMA and EFCLIN.

0.1 mm. The result is a thicker edge by about .1 mm. For an expected edge thickness of 0.5 mm, the actual edge thickness would be 0.6 mm. It is up to the fitter and patient to determine Advertisement

!AZ.indd 5 34_Larsen.indd 35

20.03.20 12:42 17:54 18.11.21

SPECIAL TOPIC

New challenges in intra-ocular lens metrology Recent functionalities and computation methods As the complexity of IOL designs increases, metrology tools must become more and more powerful. Whether they are designed to generate multiple foci or an extended depth of focus, modern IOLs embed complex surface shapes and require ever more accurate metrology tools. By Luc Joannes

36

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GlobalCONTACT 3-21

19.11.21 15:52

SPECIAL TOPIC

Besides the power and MTF benches described in the

The present paper introduces the most recent functionalities

ISO-11979-2 standard, wavefront sensors are widely used

and computation methods implemented in the IOL-Mentor

in both R&D and production environments. Besides the

software application which push the limits of IOL metrology

instrument used for the raw measurement of the lens, a

further.

dedicated data processing and user interface is key for the IOL industry.

A NEW SYNTHETIC MODEL EYE

The Phase Shifting Schlieren, on which the Nimo technology

The imaging performances of an IOL are evaluated in a lens

is based, differs from other wavefront sensors methods by its

system called ‘Model Eye’ (ISO-11979-2) accurately positioned

high spatial resolution which makes the measurement of the

in front of a wet cell containing the IOL (figure 1). The Model

most complex wavefronts possible and accurate.

Eye simulates the power and spherical aberration of the cornea.

GlobalCONTACT 3-21

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19.11.21 15:52

SPECIAL TOPIC

advantages: in R&D, from a single IOL measurement, multiple Model Eye configurations can easily be simulated and compared; in production environments, the measurements are more consistent as they are not affected by the variability of the position of the IOL with reference to the cornea model.

Ultimately, and this is non negligible, wavefront sensors and synthetic model eyes make it possible to measure IOLs in air and afterwards compute their performances in-situ and with the contribution of the Model Eye. Fig. 1: An intraocular lens in the ISO-11979-2 Model Eye. Cornea model (left) and

A straightforward method for the numerical simulation of the

IOL in a wet well (right).

effect of the synthetic cornea on the MTF consists in summing the wavefront of the IOL and the wavefront the synthetic cornea

The imaging performance of the IOL is evaluated through the

generates in the IOL plane. This method, referred as ‘paraxial’,

Modulation Transfer Function (MTF), at a specific aperture

is valid for small apertures and when both the IOL and synthetic

diameter (in the IOL plane) and for a given spatial frequency.

cornea have low aberrations, but it rapidly shows its limitations

The asphericity of the cornea model can be adjusted to match

if these conditions are not met.

the manufacturer’s requirements.

To overcome this problem, Lambda-X has developed a ‘non-

To measure the MTF, a traditional lens bench takes both the

paraxial’ ray-tracing method (patent pending) that is valid

cornea model and the IOL into consideration whereas

without restrictions on the amount of spherical aberration in

wavefront sensors can measure the wavefront of the sole IOL.

the system. In contrast to the paraxial method, this non-paraxial

The contribution of the Model Eye can later be computed via

approach accounts for the focusing effect of the Model Eye and

numerical simulations. This capability has two major

therefore for the incident light entering the Model Eye not

Fig. 2: LB1157 simulated on Zemax

Fig 3: LB1157 processed on the Non-Paraxial Model Eye of IOL-MENTOR

Fig. 4: PMMA aspheric lens simulated on Zemax

Fig. 5: PMMA aspheric lens processed on the Non-Paraxial Model Eye of IOL-Mentor

38

36_LambdaX.indd 38

GlobalCONTACT 3-21

19.11.21 15:52

SPECIAL TOPIC

THE PHASE SHIFTING SCHLIEREN, ON WHICH THE NIMO TECHNOLOGY IS BASED, DIFFERS FROM OTHER WAVEFRONT SENSORS METHODS BY ITS HIGH SPATIAL RESOLUTION WHICH MAKES THE MEASUREMENT OF THE MOST COMPLEX WAVEFRONTS POSSIBLE AND ACCURATE.

Fig. 6: An EDoF IOL captured by IOL-

Fig. 7: Complex wavefront of the EDoF lens.

Mentor and Nimo.

Fig. 8: Measured through-focus MTF on the EDoF IOL. The aperture diameter is 3 mm and frequencies are 25 lp/mm (red), 50 lp/mm (Blue) and 100 lp/mm (Green). Power, cylinder and addition are calculated from the MTF peak positions at 50 lp/mm.

being collimated. In order to apply this method, the refractive

while figure 5 confirms the perfect match of the MTF computed

index of the lens material and the overall lens geometry need

by IOL-Mentor for the lens measured in air and in-situ.

to be taken into consideration as parameters for the measurement of the IOL (or its post processing).

EDOF CHARACTERIZATION

The method has been validated against the lens design software

Nimo is also capable of measuring a large variety of extended

Zemax for multiple IOL designs including toric lenses.

depth of focus (EDoF) intraocular lenses (figure 6). Complex

A first demonstration is given in the simple case of a bi-convex

wavefronts can be captured as long as they do not include a

glass lens (Thorlabs – LB1157) which has a power of 100D in air

diffractive step structure (figure 7). The through-focus MTF at a

and a center thickness of 2.4 mm. The theoretical through

given frequency is generally used to extract the IOL power(s) and

frequency MTF in the best MTF (50 lp/mm) plane for an aperture

evaluate the imaging quality. Figure 8 shows the through-focus

diameter on 3 mm has been simulated in Zemax (figure 2).

MTF curves of a commercial EDoF IOL measured with Nimo

Figure 3 demonstrates the accuracy of the Non-Paraxial Model

and computed with the Non-Paraxial Model Eye of IOL-Mentor.

Eye available in IOL-Mentor. The MTF computed from the IOL

The cornea model has 0.15 µm of spherical aberration in this case.

wavefront measured first, in situ in a wet cell and then in air, perfectly matches the MTF simulated by Zemax. Note that the

CONCLUSION

spherical aberration of the cornea model is chosen to be 0.1 µm

The patent pending Non-Paraxial Model Eye implemented in

but IOL-Mentor allows any value between 0.00 µm and 0.45 µm.

IOL-Mentor opens way to a generalization of the use of wavefront

IOL-Mentor can deal with any type of lens (biconvex, plano-

sensors in IOL metrology for both R&D studies and production

convex) and any surface geometry (spherical, aspherical, toric,

quality check.

aspherical toric).

Since the IOL can be measured in air and as a single lens, the

The method has also been validated for a 1.5 mm thick aspherical

operation is simpler, more consistent, and beneficial to IOL

PMMA lens and for a large aperture (5 mm). Similar to the

manufacturers and ultimately contributes to a better vision for

previous example, figure 4 is the MTF simulated by Zemax

the patient. n

GlobalCONTACT 3-21

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19.11.21 15:52

HISTORY

About the use of the “gel”-contact lens Early guidebook for patients The history of the soft contact lens spans just over half a century. The first publication on experiences with the soft plastic was published by the Prague researchers Wichterle and Lim in 1964. Their experiments with HEMA to produce contact lenses in a spinning process turned out to be almost adventurous. Due to the political situation, they were unable to complete the development. This was taken on by others, but it is to their credit that today the soft contact lens is used worldwide both as a refractive aid and as a therapeutic agent. By Hans-Walter Roth

There is little instructive literature from the early years of the hydrophilic contact lens. In 1971, the first Germanlanguage field report appeared in the clinical monthly bulletins, and in 1978 the first guidebook written by an ophthalmologist was published as a pocket book for patients.

Until then, each lens manufacturer provided their own instructions for use for its product. Most of these writings are no longer preserved, now by chance a copy from the early years was found on Ebay.

This document was published by the company Ergon from Prague, it was probably written around 1972. The company, which mainly supplied their products in East Germany in 40

40_Roth.indd 40

THIS HISTORICAL EDUCATIONAL PUBLICATION CONTAINS THE MOST IMPORTANT INSTRUCTIONS FOR COMPLICATION-FREE CONTACT LENS WEAR, AND MOST OF THE RULES ARE STILL VALID TODAY. GlobalCONTACT 3-21

17.11.21 16:44

HISTORY

those years, no longer exists. There is no information about

Mercury-containing components such as thiomersal were

its whereabouts. However, their instructions for use are still

intended to prevent fungal infestation, but led to toxic

one of the standards for contact lens wear today. This

keratopathy in the sensitive eye. The alternative peroxide,

historical educational publication contains the most

originally recommended in a concentration of 10%, led to

important instructions for complication-free contact lens

tearful epithelial damage of the cornea if neutralization

wear, and most of the rules are still valid today. For example,

was faulty.

contact lens wearers were advised not to use cosmetics. Short

Before sleeping, the contact lens should be removed from

fingernails ought to avoid conjunctival and corneal injuries.

the eye. If the lens is stuck, it should be removed from the

Eye drops or ointments should not be used together with

eye immediately. The same applies if rainbow-colored rings

lenses without medical advice.

appear or the vision is fogged. After all, the symptoms of the tight lens syndrome or the overwear syndrome were already known, here you also have to remove the lens immediately. How to do that in an emergency is not explained in more detail.

NOTE ON POSSIBLE PROBLEMS The trick to moisten the eye thoroughly beforehand is not

IN 1971, THE FIRST GERMANLANGUAGE FIELD REPORT APPEARED IN THE CLINICAL MONTHLY BULLETINS, AND IN 1978 THE FIRST GUIDEBOOK WRITTEN BY AN OPHTHALMOLOGIST WAS PUBLISHED AS A POCKET BOOK FOR PATIENTS.

yet known; many an erosio corneae after a failed attempt led the contact lens wearer to the outpatient eye clinic.

The problems of dry eye are also mentioned. The room, in which one wears the lenses, is to be ventilated well, since the unsatisfactory air permeability of the lens can lead to oxygen deficit at the eye. The daily wearing time is thereby reduced.

Today, after 50 years, the soft disposable or disposable lens is one of the optics of choice, and complicated care procedures are eliminated with most replacement systems.

The biggest advance, however, is the price. Whereas the first soft hydrophilic lenses cost several hundred D-Mark each, today they cost only a few Euros. However, the risk of eye damage due to handling and hygiene errors or overlong wear remains. n

THERMAL DISINFECTION AND SAFETY INSTRUCTIONS It is also advised to clean the hands carefully before each manipulation in order not to spread pathogenic germs to the eye. The lenses must be cleaned thoroughly after wearing and then sterilized. During the heat sterilization, which was common at that time, the container should be kept under supervision, because it could burst. After the heat treatment,

Dr. Hans-Walter Roth Institut für Wissenschaftliche Kontaktoptik Ulm E-mail: institut.roth.ulm@t-online.de

the lenses may only be stored in a physiological solution, whatever was meant by that.

At that time, thermal disinfection was still a standard routine.

The commercially available disinfectants of the time led to incompatibility reactions in many cases.

GlobalCONTACT 3-21

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COLUMN

Under pressure

You may have heard about the impact that scleral lenses potentially may have on the intraocular pressure (IOP) of the eye. Is this true? And how harmful is it? Let’s see what the Contact Lens Evidence-based Academic Reports (CLEAR) papers by the BCLA (the British Contact Lens Association) have to say about this. These papers were published in the April issue of Contact Lens and Anterior Eye (open access) and consist of eleven different reports ranging from ocular anatomy and physiology to all types of lens modalities, including a special report on scleral lens fitting. The biggest hurdle for the team in writing the paper, and what generated the most discussion, was in fact IOP with regard to finding a well-balanced and evidence-based answer to the question raised above. By Eef van der Worp

GLAUCOMA First things first: there is a beautiful but delicate balance between

cornea (after applying an anaesthetic) called Goldmann

the amount of fluid that is produced by the ciliary body (which

applanation tonometry. Basically, the amount of pressure

is located at the base of the crystalline lens) and the amount

needed to flatten the cornea to a plane state is converted to a

of drainage at the trabecular meshwork (located at the base of

number that is used in practice. The units used are millimeters

the iris anteriorly, in the corner that the iris forms with the

of mercury (mm/Hg) pressure. Values under 21 mm/Hg are

cornea). The exact location of that trabecular meshwork and

generally considered a safe level, although it can be a bit more

outflow is important, but we will get to that later. If the balance

complex than that in reality, but that is beside the point here.

between the production and the drainage is ‘off’, then the pressure in the anterior chamber of the eye rises. This could

42_EefColumn.indd 42

ANCIENT SCLERALS

lead to irreversible damage to the optic nerve head at the back

Ever since the very first introduction of (glass) scleral lenses,

of the eye – this condition is called glaucoma. The visual field

there has been talk about the potential effect that sclerals could

of glaucoma patients can gradually decrease, which is usually

have on IOP. One mechanism behind that could be that the

symptomless until it is too late and only tunnel vision remains.

scleral lenses exert force on the area where the trabecular

THE PRESSURE IS ON

42

measurement) or by using a small probe that is placed on the

meshwork is located and could prevent drainage. This indeed is the area where the scleral lens typically lands and rests.

So, the pressure is on eye care practitioners worldwide to

Another theory is that the ‘seal’ caused by sclerals may influence

monitor this on a routine basis, really. The IOP as such can be

flow, and outflow particularly, of fluids in the anterior chamber.

measured quite easily using an air-puff (non-contact IOP-

So why not just measure IOP during scleral lens wear and get on GlobalCONTACT 3-21

19.11.21 15:53

COLUMN

with it? The problem is that it is hard to measure IOP during scleral

A couple of considerations for clinical practice: the values discussed

lens wear because the scleral lens is literally in the way. The air

are all averages, and relatively short-term effects were investigated.

forces or probe simply cannot be applied to the cornea during scleral

Potentially, the eye adapts to the new situation in the long run.

lens wear. So, the first set of analyses of IOP in scleral lens wear

Plus, there are huge inter-subject differences, and we cannot

always consisted of removing the lens and measuring IOP directly

predict who will spike and who will remain stable, as Joseph

after lens removal. This has the obvious advantage that the lens is

Shovlin put it in a recent column in Review of Optometry. To

not in place at the time of measurement. Using this method, some

add to the complexity, IOP measurement in keratoconus patients

found small but statistically significant increases in IOP.

(a major indication for sclerals of course) is complex in itself,

THROUGH THE EYELID

because the corneal parameters and rigidity are completely different from the normal cornea. Whether lens design, including

To measure IOP with the lens in-vivo, it makes sense to measure

non-symmetrical lens design options, is beneficial and could

the IOP not on the cornea but on the sclera just outside of the

alleviate the problem is still to be seen. Avoiding scleral lenses

scleral lens borders. There are devices that indeed can measure

in patients with progressive glaucoma seems to make sense but

IOP on the sclera or through the eyelid (no anaesthetic needed).

is not always easy. Sclerals are typically not worn ‘for fun’: there

The biggest pushback that studies with these instruments get

is usually a major indication to wear these lenses, and the benefits

is that the measurements are not the same as ‘corneal IOP’ and

should be outweighed against the risks – while monitoring visual

that the instruments are found to not be particularly reliable.

fields and optic nerve head changes. But in some other cases,

Even so, using trans-palpebral IOP (measurement through the

alternatives, including corneal GPs, hybrids or soft custom lenses,

eyelid), two studies reported an average increase of 5.0 mm/

can be considered potentially. n

Hg after 1 or 4.5h of lens wear, while one study reported a 1 mm/Hg increase in IOP after 6h of lens wear.

Sources - Barnett M, Courey C, Fadel D, Lee K, Michaud L, Montani G, van der Worp

THE HOLE STORY A good new addition to the IOP-scleral story is a study in which

E, Vincent SJ, Walker M, Bilkhu P, Morgan PB. CLEAR - Scleral lenses.

Cont Lens Anterior Eye. 2021 Apr;44(2):270-288

investigators drilled a large hole in the center of the scleral lens

- Cheung SY, Collins MJ, Vincent SJ. The impact of short-term fenestrated

and measured IOP through it. This does eliminate some of the

scleral lens wear on intraocular pressure. Contact Lens Anterior Eye

other disadvantages. The lens is still in place, and we measure

2020;43(6):585–8.

the corneal IOP values. They did report an average increase of

- Fogt JS, Nau CB, Schornack M, Shorter E, Nau A, Harthan JS. Comparison

3.8 mm/Hg. An elevation in the measured IOP can occur

of pneumatonometry and transpalpebral tonometry measurements of

quickly, as an increase was seen 1−2 min after lens application.

intraocular pressure during scleral Lens Wear. Optom Vis Sci

A limitation of this method, though, is that the ‘seal’ that a scleral lens typically creates is broken. This model could be very viable though for fenestrated scleral lenses.

2020;97(9):711.

- Huggert A. Increase of the intraocular pressure when using contact glasses. Acta Ophthalmol (Copenh) 1951;29(4).

- Samaha D, Michaud L. Bruch membrane opening minimum rim width

OPTIC NERVE HEAD OBSERVATION The best thing to do, really, is to look at the optic nerve head

changes during scleral Lens Wear. Eye Contact Lens 2021 May 1;47(5):295-300

directly and to measure the minimum rim width (MRW). Here,

- Shovlin. Pressure Cooker. Review of Optometry. 2021 Aug 15th: p74.

you can directly see and measure the effect of any potential

- Walker MK, Pardon LP, Redfern R, Patel N. IOP and optic nerve head

IOP increase, if there is any. So far, two studies have looked at

morphology during scleral Lens Wear. Optom Vis Sci 2020;97(9):661–8.

this. Maria Walker and colleagues in Houston (USA) have done some important groundwork in the field, and found a minimal effect on optic nerve head morphology in healthy adult eyes, using the non-scleral-lens-wearing eye as a control. Conversely, Samaha et al. from the University of Montreal (CA) observed a small but significant reduction in Bruch’s membrane opening minimum rim width after complete lens settling.

TAKE HOME MESSAGE The take home message for clinical practice is that scleral lenses could alter IOP to some degree. But, the jury is still out, and definite conclusions cannot be drawn at this point based on the current evidence, the CLEAR paper states.

GlobalCONTACT 3-21

42_EefColumn.indd 43

Eef van der Worp, BOptom, PhD, FAAO, FIACLE, FBCLA, FSLS is an educator and researcher. He received his optometry degree from the Hogeschool van Utrecht in the Netherlands (NL) and has served as a head of the contact lens department at the school for over eight years. He received his PhD from the University of Maastricht (NL) in 2008.

He is a fellow of the AAO, IACLE, BCLA and the SLS. He is currently adjunct Professor at the University of Montreal University College of Optometry (CA) and adjunct assistant Professor at Pacific University College of Optometry (Oregon, USA). He lectures extensively worldwide and is a guest lecturer at a number of Universities in the US and Europe.

43

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MISUPCOTM MisupcoTM Inc. MisupcoTM Inc. 1378 Osceola Avenue 1378 Osceola Avenue Saint Paul, MN 55105 Saint Paul, MN 55105 USA

LAMBDA-X S.A. Avenue Robert Schuman 102 B-1400 Nivelles Belgium

Larsen Equipment Design 1117 N.W. 52nd Street Seattle, WA 98107 USA

Phone: +32 67 79 40 80 Fax: +32 67 55 27 91

Phone: +1 206 789 5121 Fax: +1 206 789 7756

Phone: +1 651 353 8632 Fax: +1 651 698 0719 Fax: +1 651 698 0719

info@lambda-x.com www.lambda-x.com

erik@larsenequipment.com www.larsenequipment.com

mikef@misupco.com mikef@misupco.com www.misupco.com

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Machinery and Tools

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USA

Phone: +1 651 353 8632

www.misupco.com

Blocking Wax

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Optimec Systems Limited Unit B3, The Haysfield Spring Lane North Malvern, WR14 1GF United Kingdom

OPTOCRAFT GmbH Am Weichselgarten 7 D-91058 Erlangen Germany

SCHNEIDER GmbH & Co. KG Biegenstrasse 8 –12 35112 Fronhausen SCHNEIDER GmbH & Co. KG Biegenstrasse Germany 8 –12

Phone: +44 1684 607006

Phone: +49 9131 691500 Fax: +49 9131 691511

Phone: +49Germany (64 26) 96 96-0 Fax:Phone: +49 (64 96 96-100 +4926) (64 26) 96 96-0

www.optimecsystems.com info@optimecsystems.com

sales@optocraft.de www.optocraft.de

info@schneider-om.com info@schneider-om.com www.schneider-om.com www.schneider-om.com

35112 Fronhausen

Fax: +49 (64 26) 96 96-100

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Instruments

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Sterling Ultra Precision Division of AMETEK Precitech Inc. 8600 Somerset Drive, Largo Florida, 33773 USA Phone: +1 727 538 6110 fadi.achkouti@ametek.com Europe: +49 98 3797 8238 andreas.kuchler@ametek.com www.sterlingint.com

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TRIOPTICS GmbH Strandbaddamm 6 22880 Wedel Germany Phone: +49 4103 18006 0

V-Optics SAS 2, rue du travail 67400 Illkirch-Graffenstaden France Phone: +33 (0) 3 67 10 28 60

www.trioptics.com sales@trioptics.com

Instruments

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info@v-optics.fr www.v-optics.fr

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MASTHEAD

THE DIGITAL GLOBALCONTACT

The App on your tablet, smartphone or computer.

GLOBAL CONTACT The Website and the Magazine: The complete communication system for the contact lens industry. The magazine, 2,500 copies, is distributed to contact lens laboratories, wholesalers and other organizations active in the contact lens and IOL industry.

The website www.global-cl.com is free for all industry related professionals PUBLISHERS ADDRESS Eyepress Fachmedien GmbH Saarner Str. 151, D-45479 Mülheim a. d. Ruhr Tel.: +49-208-306683-00 Fax: +49-208-306683-99 Website: www.global-cl.com E-mail: info@global-cl.com CEO Petros Sioutis E-mail: p.sioutis@eyepress.de PUBLISHER Silke Sage, Efstathios Efthimiadis, Petros Sioutis EDITOR-IN-CHIEF Dipl.-Ing (FH) Silke Sage E-mail: silke@global-cl.com EDITOR Britta Laupichler E-mail: britta@mafo-optics.com TRANSLATIONS John Saniter, Bopfingen, Germany EDITORIAL BOARD Wim Aalbers, Erik Larsen, Eef van der Worp PRODUCTION & LAYOUT Efstathios Efthimiadis DISTRIBUTION PressUp GmbH, Postbox 70 13 11, D-22013 Hamburg Tel.: +49-40-386666-308, Fax: +49-40-386666-299 MEDIA CONSULTANT Constanze Classen Tel.: +49-208-306683-20 Fax: +49-208-306683-99 E-mail: constanze@global-cl.com ADVERTISING AGENT GREAT CHINA Beijing FOCUS Optics Culture Commnication Co. Ltd. Room 319, Building 2, Nr. 1, Northbank 1292, Nr. 15 Jianguo Eastroad, Beijing 100024 (Chaoyang), P.R. China Mrs. Jian Wang Tel.: +86-10-8537-6529 Email: jennywang_focus@126.com Skype: jennywang611 ADVERTISEMENT RATES Price list No. 10, valid from January 01, 2021 Publication Schedule 3 issues 2021: March, July, November

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BANK DETAILS Bank account: Sparkasse Aachen IBAN: DE21 3905 0000 1073 3925 06 SWIFT: AACS DE 33XXX PRODUCTION & PRINT Kollin Mediengesellschaft mbh, Neudrossenfeld The publisher takes no responsibility for unsolicited manuscripts. Please note also that photographs submitted for use in GlobalCONTACT cannot be returned. The publisher's written permission is required for any reproduction, translation or recording of material published in GlobalCONTACT, including extracts of such material. Permission will normally be given, subject to the usual acknowledgement. Copies made of published items must be limited in number and for personal use only.

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48th

EFCLIN

EUROPEAN FEDERATION OF THE

CONTACT LENS AND IOL INDUSTRIES

CONGRESS EXHIBITION

28TH – 30TH APRIL 2022 BARCELONA/SITGES, SPAIN

A WORLD OF OPPORTUNITIES 2022

Spanish culture combined with ancient and modern science has found Sitges/Barcelona to be the perfect location for business and leisure time as well. The 48th EFCLIN Congress & Exhibition takes place there from 28th – 30th April 2022. For an engaging lecture program, manufacturer’s forum and the best trade exhibition in the business, it can’t be beaten. It’s where the Contact Lens & IOL Industry from Europe, the Far East, North America and beyond come together… will you be there?

REGISTER NOW WHILE THERE IS STILL TIME AT

www.efclin.com/congress or e-mail us on info@efclin.com Comsy_Ins_EFCLIN_2022_A4.indd 1 !AZ.indd 3

MORE INFORMATION WEB www.efclin.com MAIL info@efclin.com PHONE +41 41 372 10 10 FACEBOOK search: EFCLIN TWITTER @EFCLIN#efclincongress ADDRESS EFCLIN | Winkelbüel 2 | CH-6043 Adligenswil | Switzerland

27.04.21 14:22 25.10.21 12:03

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BIG DAC Offers Tooling Options That Grow With Your Business.

6390 Rose Lane, Carpinteria, CA 93013 USA Phone +1 805 684 8307 Fax +1 805 566 2196 dac-intl.com Chris Pantle +1 805 745 1610 cpantle@dac-intl.com Kurtis Brown +1 805 745 1628 kbrown@dac-intl.com

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02.11.21 12:17