discovering dry eye
The Effect of Environment On Dry Eye
BY KELLY KINNEY NICHOLS, OD, MPH, PHD

The hygrometer in my office currently reads 50 percent water vapor in the air. In a carefully controlled experiment, I then placed my hygrometer on the ledge of my second-floor window for 30 minutes to determine the outdoor air vapor reading, given that it rained this morning. The new reading was 70 percent, and the weather report this morning predicted 77 percent humidity. Does the outdoor or indoor humidity influence the ocular surface? Would the ocular surface by more affected in a contact lens wearer?

Anecdotally, there are "rumors" of how difficult it is to fit contact lens patients in dry climates. Interestingly, numerous contact lens practices thrive in dry places such as Denver. In a location like Denver where outdoor recreation is popular, there may be more contact lens wearers for that reason (and more practitioners, for that matter).

Contact Lens Wear and Environment

In theory, if a dry environment had a negative impact on the tear film, and this negative effect led to contact lens discomfort and contact lens-related dry eye, then one could speculate that there would be fewer contact lens wearers (adjusted for the population) in "dry regions." To my knowledge, the number of contact lens wearers per state is not known. However, contact lens sales could be influenced by a number of factors including access to care, socioeconomic status and mode of contact lens wear. Using sales data alone as a proxy for the frequency of contact lens wear could be misleading.

Ohio is humid in the summer. The hygrometer on my desk does not vary drastically over the year. This probably has to do with the poor air circulation in our old building at the College of Optometry. If the environment has an impact on the ocular surface, clinicians and researchers must consider where the patient spends the most time. The hygrometer on the ledge outside now reads 75 percent, so my indoor and outdoor environments are significantly different. Both, however, are higher in humidity than many dry environments.

Airplanes and Other Research

A few studies have looked at dry eye symptoms among air travelers due to low humidity in airplane cabins. Nagda and Hodgson (2001) report that exposure of three to four hours in a low humidity environment produces symptoms of mucosal irritation in flight attendants and passengers. Backman and Haghighat (2000) reported that among commercial airplanes, air quality was poorest on the Airbus 320 and highest on the DC-9.

In terms of the tear film in non-contact lens wearers, humidity has been shown to have an effect on lipid layer thickness and tear film stability. Higher periocular humidity while wearing moisture-chamber goggles leads to increased tear film thickness and decreased dryness symptoms (Korb et al, 1996). Moderate to total relief of symptoms occurred when humidity in the goggle chamber was high, with the results persisting one to three hours following goggle removal. The increased comfort associated with higher humidity levels has led to treatment modalities designed to raise periocular humidity, including wearing spectacles with side shields (Tsubota, 1989).

Whether you practice in a dry or a humid location, patients will want to wear contact lenses. If a contact lens patient reports discomfort, evaluate the environment in which he wears his contact lenses along with contact lens fit as possible culprits. A low humidity workplace or home can be remedied with an inexpensive humidifier if other causes for contact lens discomfort are ruled out.

Dr. Nichols is assistant professor of clinical optometry at The Ohio State University College of Optometry in the area of dry eye research.