discovering dry eye
New Studies Shed Light on Contact Lens-Related Dry Eye
BY JASON NICHOLS, OD, MS, FAAO, AND KELLY KINNEY NICHOLS, OD, MS, FAAO
Contact lenses interfere with the tear film and place additional demands on the structures responsible for its production. Minor deficiencies of this functional unit that produce no symptoms under ordinary conditions may result in dry eye symptoms during contact lens wear.
under ordinary conditions may result in dry eye symptoms during contact lens wear. Although we do not fully understand the etiology of contact lens-related dry eye, some of the following studies were presented at the recent Third International Conference on the Lacrimal Gland, Tear Film and Dry Eye Syndrome in Maui, HI, which may help unravel this clinical disorder.
Epidemiology and Symptoms of Dry Eye During Lens Wear
The Harvard Dry Eye Epidemiological Studies (Schaumberg et al, 2000) is evaluating the prevalence and factors associated with dry eye syndrome in two large cohorts: The Women's Health Study (39,876 female health professionals) and the Physicians Health Studies (25,000 male physicians). Preliminary findings show that the overall incidence of dry eye syndrome is 6.6 percent in women and 2.8 percent in men. In both men and women, the incidence of dry eye syndrome increased with age. Use of hormone replacement therapy in post-menopausal women was significantly associated with a higher prevalence of dry eye syndrome.
Further findings showed that 15 percent of contact lens wearers were diagnosed with dry eye. With about 35 million contact lens wearers in the United States, it is likely that about 5.25 million of them suffer from contact lens-related dry eye syndrome. With the aging baby boomer generation, we expect the prevalence of contact lens-related dry eye syndrome to increase as we move into the next millennium.
Tear Film and Contact Lens Interaction
Some feel that contact lens wear alters the composition of the tear film. Guillon et al. (2000) pre-sented work in support of this theory. Using laboratory techniques, they analyzed the lipid layer of the pre-lens tear film on a group of hydrogel lens wearers. An excessive level of cholesterol esters in the pre-lens tear film indicated an unstable lipid layer and symptomatology during lens wear. This supports the concept that an unstable lipid layer is responsible for contact lens-related dry eye.
Finally, Nichols and King-Smith (2000) presented research on the thickness of the pre- and post-contact lens tear film. A lens divides the pre-corneal tear film into two layers. The new tear layers must perform the functions of the precorneal tear film for successful contact lens wear. Some of the functional characteristics of the tear film during contact lens wear include antimicrobial properties, ocular surface lubrication, debris removal, lens hydration and optical surfacing.
Interferometry was used to measure the tear film layers and contact lens thickness in vivo. Preliminary studies show that the mean pre-lens tear thickness is around 2.35 µm, while the mean post-lens tear thickness is around 2.45 µm. This value of post-lens tear thickness is considerably smaller than the value of 11 to 12 µm found by previous studies.
Dry eye symptoms cause many contact lens patients to reduce their wearing time or discontinue lens wear completely. Future studies on the structure and function of the tear film during contact lens wear may provide insight into the mechanisms behind common symptoms during contact lens wear. The type of research presented at this meeting is integral to our understanding of how the tear film and contact lens interact during lens wear.
Dr. Jason Nichols is an advanced practice cornea and contact lens fellow at the Ohio State University College of Optometry.
Dr. Kelly Nichols is assistant professor of clinical optometry at The Ohio State University College of Optometry in the area of dry eye research.