discovering dry eye
BY KELLY K. NICHOLS, OD, MPH, PHD
As I sit here, marginally aware of my contact lens (dis)comfort, I wish for contact lenses that I can't "feel" in my eyes. I'm sure that I'm not alone. While the contact lens industry gains many new wearers each year, a significant number of contact lens dropouts create a relatively flat market. If we could just keep patients like me happier -- if we could solve the comfort game -- then industry and clinicians alike would rejoice.
Figure 1. Interferometry patterns of the pre-lens tear film 15 seconds after the blink.
Stuck on You
As Lionel Ritchie sings in his song by the same name: "I've got this feeling down deep in my soul that I just can't lose." It's my feeling that the fundamental issue that affects contact lens comfort may relate to the contact lens surface and its wettability.
This certainly isn't a new idea, although scientists are currently evaluating it with many new techniques. Researchers have been studying the surfaces of contact lenses for years, both in terms of how wettable they are and in terms of what sticks to the surface (and what lodges in the contact lens matrix). The ultimate lens surface would remain wettable the entire time it's in the eye and would attract minimal deposits over both the short and long term. We want contact lens surfaces to mimic the true ocular surface.
Figure 1 demonstrates interferometry patterns of the pre-lens tear film 15 seconds following a blink. The streaky, lighter colored areas are the exposed surface of the contact lens. The interferometric patterns are areas where the tear film still covers the lens. As I look at this photograph (courtesy of P. Ewen King-Smith, The Ohio State University), I think it's no wonder that patients can regard contact lenses as uncomfortable. And the researchers used a normal, successful patient for this photograph. What happens when other factors, such as ocular allergy or too much time spent in front of a computer monitor, enter the picture?
Dry Eye is Multifactorial
If we've learned anything over the past few years, it's that dry eye isn't a simple disease. Several medications, systemic diseases and environmental triggers can all play a role in disrupting the balance of the tear film on the ocular surface. Our understanding of the mechanisms involved in contact lens comfort is relatively slim in comparison to the absolute data that exist regarding the oxygen permeability of materials.
Although we can increase the amount of oxygen that reaches the ocular surface, which creates a more comfortable environment for some individuals, it doesn't answer the comfort question completely. Understanding why increased oxygen improves lens comfort for some patients and not for others is challenging. Tear chemistry, lens materials and the huge unknown category of "patient factors" influence comfort.
In the future, scientists will modify lens surfaces to mimic the ocular surface and will formulate solutions that maximize in-eye biocompatibility. But we can't change the mechanical lens-to-lid interaction and patient perception of "comfort." A multi-disciplinary approach may prove just what we need to resolve this multifactorial comfort "game."
Dr. Nichols is assistant professor of clinical
optometry at The Ohio State University College of Optometry in the area of dry eye research.
Contact Lens Spectrum, Issue: April 2005