Continuing education CET The type of blink required for optimum blink efficiency has the following characteristics:
● An efficient blink is full and complete, meaning that the top lid lightly touches the bottom lid ●A n efficient blink is relaxed and light, meaning that only the muscles of the eye are involved. Specifically, the muscles of the eyebrows and cheeks are not involved
● An efficient blink is quick and rapid, taking only one third of a second to complete ● Finally, an efficient blink looks confident and natural Figure 2 Extract from a blink exercise sheet3
environmental factors including the growing use of visual display devices and exposure to air conditioning/central heating at work and in the home. How disabling a symptom may be is likely dependent on the individual. Some patients have a higher tolerance for ocular irritation compared to others. Other patients may stop or avoid certain activities but may not consider this to be related to how their eyes feel. Asking patients specific questions about how eye irritation or discomfort may prevent them or reduce their ability to perform certain activities, such as reading or using a computer, can help in determining the impact of symptoms. The impact of the symptoms may be recorded by reference to a grading scale (Figure 1). Specific questions about length of comfortable computer use in hours can help track changes over time with or without treatment. Blink rate Given that evaporative dry eye is the most common form of tear deficiency seen in routine optometric practice, failure to consider the need to improve blink efficiency may significantly undermine efforts to improve tear function in general. The normal apposition of the lids during a complete blink promotes lipid secretion from the meibomian glands. The lipid layer is spread across the cornea by the upper lids and inefficient blinking may be associated with poor maintenance of lipid layer integrity. For example, during prolonged reading, when blink rate and blink completeness are significantly reduced, the lipid layer can thin and virtually disappear before reappearing with conscious blinking. It is possible that reduced lipid flow associated with inefficient blinking contributes to stasis and gland blockage. In addition, lipid flow from glands that have been unblocked with warm compresses, lid massage and cleansing may not maintain their patency and so elapse to a blocked state if blink inefficiency is not remediated. Apart from the potential to contribute to reduced lipid flow, incomplete blinking effectively doubles the inter-blink interval
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and increases the potential for increased tear layer loss by evaporation from the areas of conjunctiva and cornea which are exposed by an incomplete blink. Although deliberate, forceful blinks promote secretion from unobstructed glands, they have a tendency to produce debris in the tear film leading to transient blurring. Patients will prefer not to blink rather than depend on conscious forceful blinking episodes. It may be better to try to achieve longer lasting benefits from improved unconscious blink efficiency. Figure 2 shows a blink instruction sheet. Failure to address blink efficiency where a need is indicated may have greater significance with computer use and/or with other forms of reading and close vision demands. Such activities are associated with reduced blink efficiency and this may be exacerbated with concurrent exposure to central heating or air conditioning. At present, there is no single ‘gold standard’ test for developing a clinical diagnosis of dry eye; therefore, a battery of tests is generally employed in clinical practice (as well as for research purposes) to define ‘dry eye’. Remember, however, to always carry out the least invasive tests first as you want to minimise the disruption to the tear film if you are attempting to measure and monitor changes to factors such as the tear quantity, quality and stability (Table 1). Ideally carry out the tests in the same order, under the same conditions and where possible the same time of day at each visit to aid comparison of results to make better informed decisions on ongoing management plans. Dry eye evaluation must also be multifaceted. In addition to assessing tear volume, quality, and stability, it is necessary to interpret staining patterns and complete a full lid evaluation to rule out the presence or co-existence of blepharitis. There is overlap of many symptoms of dry eye disease and blepharitis, so careful clinical evaluation is important. Meibomian gland dysfunction (MGD) The International Workshop on Meibomian Gland Dysfunction report
revealed that MGD may actually comprise the majority of dry eye disease. DEWS: ‘Meibomian gland dysfunction (MGD) is a chronic, diffuse abnormality of the meibomian glands commonly characterised by terminal duct obstruction and/or qualitative/quantitative changes in glandular secretion.’4 In MGD, the meibomian glands are frequently obstructed, affecting the volume and quality of the oily secretions. The result is tear film instability, which can lead to ocular surface damage and inflammation, and, commonly, to symptoms. However, despite the frequency of presentation, MGD remains relatively poorly managed in clinical practice. The chronic nature of the condition requires that therapy be applied regularly, and with long-term commitment. Management of MGD typically includes warm compresses, massage and lid ‘scrubs’ known to improve lipid layer thickness and, in turn, reduce tear evaporation. The goal of MGD management is two-fold: ● To assist the remaining meibomian glands in producing more and better quality lipids ● To reduce inflammation of the glands, this is nearly always present. Warm compresses and eyelid massage. The ‘warmth’ helps to overcome the elevated melting point of lipids inspissated within the glands. It is important to note that although many text books suggest the use of warm flannels, they rarely reach or indeed maintain the temperature required to melt these inspissated lipids and repeated removal and reheating of the flannel is required. There are, however, a number of commercially available devices from the simple and inexpensive MGDRx EyeBag and iHeat devices through to 25.11.11 | Optician | 31