Context in contacts

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

EPONYMS

The impressive British Contact Lens Association (BCLA) CLEAR papers – in which CLEAR stands for contact lens evidence-based report – shine an interesting light on terms used in our field. Laura Downie from the University of Melbourne in Australia is the lead author of part one of that series (eleven papers in all) that focuses on the anatomy and physiology of the anterior eye. She composed this paper with a team of experts from around the world including some European hotshots. Everybody who is active in the contact lens field should maybe have a look at this (the papers are open access from the Contact Lens & Anterior Eye website) to understand the landing tarmac of the lenses we so dearly love. The first thing the committee notes is that in general, the trend is to avoid eponyms where possible. An eponym is a person, place, or thing after whom or which someone or something is, or is believed to be, named. An example is Zeppelin (the first balloon with propellers that was directable), which is derived from the name of the German general and aeronautical pioneer Ferdinand von Zeppelin. In the cornea alone, we have several eponyms, the first being

Bowman’s layer after the English physician, anatomist, and ophthalmologist William Bowman (1816–1892). This layer is thin but very strong. It separates the corneal epithelium anteriorly from the stroma. The new term for this, which would directly point to its location in the cornea and, to some degree, to its function, would be anterior limiting lamina. Don’t be surprised to see that term appear in future papers. The same is true with Descemet’s membrane (after the French physician Jean Descemet, 1732–1810). This would now become posterior limiting lamina, as it separates the posterior part of the cornea (the stroma) from the endothelial layer. There is discussion to do the same with Meibomian glands (after Heinrich Meibom, a German physician who lived from 1638–1700 and who first described these). There was no consensus within the CLEAR team at this point to change this to tarsal gland, but that may change in the future too.

“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 do matter: a systematic review on how different terminology for the same condition influences management preferences”. In this systematic review, they look at several medical conditions and how they are described. One of them happens to be from the eyecare field; to describe the condition of conjunctivitis, you could use the term Pink Eye, or you could refer to it as Eye Infection. One can imagine how this could have a huge impact on behaviour. And it does. Different terminology given for the same condition influenced management preferences and psychological outcomes in a consistent pattern, according to the study. Changing the terminology may be one strategy to reduce patient preferences for aggressive management responses to low-risk conditions. So, here is something to think about – from eye care practitioners toward their patients and also from manufacturer to client, and in everyday life on an almost constant basis, really – be careful what words or phrases you use in any given situation. It may change the outcome.

CONTACT LENS SAFETY

One ‘biggie’ in our field, of course, is contact lens safety. In many countries, there are unfortunately hefty discussions between ophthalmologists and contact lens specialists on the safety of orthokeratology. Is the ophthalmology world right? Depends on how you look at it, I suppose. If you see a number of MK (microbial keratitis) cases in a given week because of orthokeratology I can imagine that you may wonder whether this is the right modality (for children particularly). So, there is work to do: we need to make our contact lens practices as safe as possible, and there is room for improvement. Acanthamoeba infection, for instance, is almost exclusively contact lens-related and is also linked to tap water. Hence, it has been called a ‘preventable disease’. At the same time, all practitioners in large practices with whom I’ve spoken who do a lot with orthokeratology report hardly any cases of corneal infection with the modality in their database. It almost seems as though for the experts in the field who are on top of things, the infection rate is not all that high. But every infection is one too many. How to deal with this, in general, when you fit a pair of contact lenses? On one hand, you don’t want to scare newbie lens wearers. Contact lenses are a safe modality; pretty much everybody is on board with that. On the other hand, you don’t want to downplay things. You want to make sure that patients are compliant, that they follow the rules and regulation, and that they understand that there is a risk of infection. A little bit of good information about these risks 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!

Another term that most likely will become more relevant going forward and will become the new standard in the contact lens field is ‘micron’. Microns of height are the new millimeters of radius in contact lens terminology. As we are moving away from central keratometry values to full corneal topography, we are also starting to think in elevation and height. The

appropriate term for that is micrometer (micron): which is, of course, 1/1000th of a millimeter. The decision on when to fit a spherical corneal lens versus a toric corneal lens can now be made based on microns of height (typically in the 30-micron range is the cut-off point). This is true, too, for spherical versus toric orthokeratology. Also, the decision on when to go from a corneal lens to scleral lens is height dependent; studies at Pacific University have found that in 88% of cases, patients with less than 350 microns of corneal elevation difference along one meridian (the one with greatest variance) had good success with a corneal lens. But if there is more irregularity than that, then a scleral lens could be indicated. To top it off: when fitting scleral lenses, when is a toric scleral lens needed as an upgrade from a standard spherical scleral lens? We know from research by Greg DeNaeyer et al that if a 16 mm circle is drawn onto the scleral surface concentric to the limbus, less than 6% of eyes have a scleral asymmetry of more than 300 microns at 16 mm, which is considered ‘spherical’ by that definition. Anything more than that may be eligible for a toric or asymmetrical scleral lens design.

Scleral lenses have really opened our minds, and the road, toward using microns; everything from the elevation on the ocular surface, to clearance (fluid reservoir, vault) and trial sets for sclerals is in the micron nomenclature. And soft contact lenses are presented in overall sagittal height now too (in microns) – see my last contribution to GlobalCONTACT: ‘Mind the Gap’.

A THIN SKIN

To put things in perspective, and circling back to the anatomy and physiology of the anterior eye CLEAR paper, the thickness of the cornea is 540 microns and is considerably thinner in keratoconic eyes. The cornea is comprised of five principal layers, of which the most anterior layer (the epithelium) is approximately 50 microns thick. Extremely important tissue, of course, when it comes to orthokeratology. You may want to indent or massage that epithelium to some degree, but not the full thickness. 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 thick. To get a good perspective of things, it would probably be better to switch to microns. You see that in dealing with these layers and with our lenses, we are talking about very small numbers. People may be ‘thin-skinned’, as a figure of speech, when it comes to leaving curves behind and/or switching from millimeters to microns. But students in schools now start to think in microns first, with curves ‘second’. It may be time to move on.

AXL

Extending this to a new standard of care entering our field, myopia management: trying to not make this a lengthy article, myopia management is all about length. Myopia is an axial length disease. So, to keep it short, when you follow change in myopia development, it is all about axial length (AXL) of the entire eye. Managing myopia based on subjective or objective refraction is much too variant, and 0.25D steps are too coarse. At the recent ARVO meeting – the research congress in the ophthalmic field – the six-year data of a soft lens for myopia management (MiSight) was presented. This data showed that the maximum average change in six years that can be achieved is about half a millimeter: 0.529 mm, to be precise. Why not put this in microns? 529 microns sounds more exact and more applicable. In the MiSight study, 0.25D change in myopia was considered equal to 0.1 mm change…or shall we use 100 microns? Average growth of the eye between 10 and 13 years of age was 90 microns per year in the study, while for myopes not receiving treatment this was 160 microns annually. But the point is, shall we use microns here (instead of 0.09 mm and 0.16 mm, respectively, in this case)? To follow change, this AXL measurement needs to be repeated on a regular interval (probably every six months). The changes are subtle; there is some discussion on what normal change is, and it may be dependent on the amount of myopia. But in any case, a parent would be more impressed if our treatment reached 110-micron reduction in myopia progression rather than 0.11 mm, presumably.

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

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.