Soft Special Edition
Soft lens comfort:
What are we missing?
Professor at École d'optométrie de l'Université de Montréal and Chief of the Contact Lens Department - Montreal, Quebec, Canada
The first report about contact lens discomfort (CLD) was published more than 50 years ago (Szekely, 1960), shortly after the commercialisation of soft lenses. Since then, industry has brought to the market innovative products and contributed to the development of new materials, new modalities of wear, and new contact lens care products. All of these improvements were made to significantly improve contact lens comfort. Despite these efforts, CLD remains the first symptom to be reported by patients and is considered the main factor leading to dropout of soft lens wear (Dumbleton, 2013).
As a consequence, for the last 25 years, contact lens industry growth has been characterized by a flat curve, with no real hope of reversing this tendency. Data published by the industry indicates that the value of lenses sold is rising, but not the number of patients wearing this modality around the world (Richdale, 2007).
How to Drop the Dropout
Everybody should be concerned because the dropout rate not only constitutes a net loss for the industry, but also for practitioners who are spending time and money fitting lenses on their patients. What can we do to reverse the curve? What are we missing?
In 2013, the TFOS (Tear Film and Ocular Surface Society) international experts group on Contact Lens Discomfort tried to provide answers to this question by analyzing the published work of many experts who have tried to understand this phenomenon, from back in the 80’s to modern days. They developed a nice definition of CLD (Nichols, 2013), which helped to establish the basis for a common understanding. They also realized the paucity of trustable sources, being unable to rely on well-conducted, randomized, prospective trials done in the field. Most of the evidence is not strong enough to allow a complete understanding of the phenomenon, coming from anecdotal case reports, small-sample clinical studies that are not so well designed, or sponsored-clinical reports on the usage of new technologies. It is then difficult to make a valuable evaluation on the real causes leading to CLD.
However, at the end of their analysis, International experts finally concluded that CLD is patient-related and multifactorial in origin (Dumbleton, Caffery 2013). Because it is highly variable in severity and clinical presentations, they stated that it is difficult to establish a common pattern and, consequently, hard to define ways to lower CLD occurrence with a single method applicable to everybody.
Under the Radar
The TFOS meeting also pointed out interesting things that went under the radar for a long time, such as subtle neurological changes at the corneal epithelial level and modifications of the tear film exposed to lenses and care products. More recently, other authors proved that contact lens fitting may not be optimal and may interfere with ocular surface integrity (Young, 2001). This new finding could really be the missing link to understand why our patients are still dropping out, no matter which materials, modalities, care products or personal factors are involved. Let’s explore.
A contact lens should be considered as a foreign body triggering several sources of stress on the ocular surface. The first stress to occur comes from its impact on the tear film stability. As a consequence, tear film osmolarity increases (Stahl, 2009), and the ocular surface becomes a pro-inflammatory land. The second stress is mechanical in nature, driven by the way the lens fits on the ocular surface. Up to now, there has been no consensus on the ideal soft lens fit on the eye, especially if we consider the sagittal height of the lens compared to that of the ocular surface (Van der Worp, 2014). What is known, however, is that a lens that does not fit well will induce a negative outcome on the corneal and conjunctival epithelia. This stress can also induce inflammatory reaction. The surface of the lens itself generates the third source of stress on the eye. Brennan and others (Jones, 2013) identified the coefficient of friction of a material as the key element leading to CLD. Korb (2002) associated lid wiper epitheliopathy, second to friction, as related to CLD in a significant percentage of patients. The chronic presence of such epitheliopathy is certainly increasing inflammation on the ocular surface.
Reusable lenses gather deposits and harvest pathogens. Deposits increase material friction on the eye and destabilize the tear film even more. This adds to the stress generated by the presence of the lens on the eye. Pathogens release toxins that stimulate the immune system to react. This is especially true if we consider the back surface of the lens, which is not exposed to blinking and is where pathogens are more likely to be found. If a lens is fitted inappropriately – too tightly, for instance – these toxins will remain trapped under the surface of the lens. Sterile infiltrates, especially found in silicone hydrogel wearers, can be explained in part by this reaction (Jones, Powell, 2013). To add to this “toxic-soup” phenomenon, the biocides and chemicals adsorbed in the lens are released during the first hours of lens wear, contributing to challenging the ocular surface, especially if they remain trapped under the lens.
The Sum of Stresses
If we consider the sum of these stresses, we can hypothetically suggest that contact lens wear is associated with a chronic sub-clinical inflammation of the ocular surface, starting as soon as the lens is inserted. This inflammatory reaction builds up over the weeks, months and years to the point of reaching a threshold level where it becomes visible. CLD comes from this reaction.
This hypothesis also explains the variability of ocular response among wearers: some patients can survive to a high level of stress, with no symptoms, while others are more fragile and more sensitive. Some will not be able to successfully wear contact lenses after a few months whereas others will not show significant symptoms until after a number of years. The reality is that everyone, at a given point, will reach this threshold. With aging, because of the physiological natural changes occurring on the ocular sur
face and affecting the tear film, stresses increase and the threshold is more easily reached.
If considering contact lens wear as a pro-inflammatory event helps to solve the puzzle, then the next step is obvious: why not proactively treat the ocular surface with anti-inflammatory medication before/after lens wear? It would not be the right thing to do, considering the preservative agents and the side effects of such medication over time. Personally, I prefer more “ocular-friendly” approaches.
"This means we need to completely revisit the way we are fitting lenses now and go back to the drawing table."
This can be achieved by minimizing the risk factors and alleviating inflammatory component buildup on the eye. The first step is to assess the ocular surface and to optimize the tear film stability prior to lens fit and wear. Second, we have to select materials with the least potential to induce stress on the ocular surface. This means single-use (daily disposable) lenses (SUL) with the lowest coefficient of friction, the best biocompatible surface, and a reduced modulus. SUL can also help lower the bioburden (deposits and pathogens). More importantly, with SUL, care regimens – with their biocides and preservative agents – are kept out of the equation.
Sell Your Keratometer
Finally, fitting the lenses to alleviate mechanical impact on the ocular surface is a must. This last step is not anecdotal. This means we need to completely revisit the way we are fitting lenses now and go back to the drawing table - and pay attention to the research in this field. For the moment, let’s say that a lens should be extending beyond the limbus by 1 mm in every quadrant, and that the lens has to move enough upon blinking to favor tear exchange. This means that diameter is more important than base curve (sell your keratometer) and that clinical observation of the lens on the eye is crucial, especially after several hours of wear.
In conclusion, this hypothesis makes sense on paper. It is necessary to pursue research work to prove it. At the least, it opens the door to a brand new challenging environment in soft lens fitting. Are you ready to enter?
Dr. Langis Michaud graduated from École d’optométrie de l’Université de Montréal in 1986, where he also obtained his Master’s Degree in physiological optics (1998).
Dr. Michaud is a full professor and has practiced at Université de Montréal since 2001, as the chief of the contact lens department. He is Fellow of the American Academy of Optometry (Diplomate), the British Contact Lens Association and the Scleral Lens Education Society. He is a member of the European Academy of Optometry.
Dr. Michaud has published numerous articles in peer-reviewed journals and publications or professional reviews. Because of his expertise, he has often been invited to speak in Europe, Asia, and United States.
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