discovering dry eye
Ethnic Differences in Lens Response and Tear Film
BY BARBARA CAFFERY, OD, MS, FAAO
Recently, an interesting area of research has arisen. Discussions have begun on the differences in physiological responses between Caucasian and Asian contact lens wearers. Professor Ken Polse and his Berkeley research group measured the corneal epithelial barrier function to fluorescein immediately after extended overnight wear of high and low Dk lenses. In both lens types, they noted a statistically significant increase in epithelial permeability in the Asian population as compared to the Caucasian group.
The Berkeley group then measured the post lens tear film thickness (PLTT) of 94 subjects, 53 of whom were Asian, and found the PLTT to be significantly less in the Asian group. The theory is that the lid tension and reduced aperture size found in the Asian population reduces the PLTT, causing more trapped debris behind the lens and therefore more disruption of the epithelium and increased epithelial permeability. Whether these facts translate into increased risk for infection is not known but deserves further investigation.
Dr. Jean Jacobs has added to this concept through her research on the differences between Asian and Caucasian endothelium during lens wear. Using the confocal microscope to observe the corneas, she found that Asian eyes had a much higher bleb response than the Caucasian corneas.
There was some clinical discussion about ethnic differences observed by the clinicians in the group. It was noted by some that Asian eyes tended to have superior epithelial arcuate lesions (SEALs) more often that non-Asian eyes, and this finding was connected to the tightness of lids.
Gender issues have been well documented by many researchers including Holly, Pfluegfelder, Tomlinson, Begley and Nichols, but have we looked carefully enough at differences between genders and ethnic groups? Tear epidermal growth factor was found in higher concentrations in men than in women. Clearly females experience dry eye at an earlier age than men. Also, more women have autoimmune-related dry eye diseases than men.
Ethnic differences have not been as well studied. A recent paper out of Australia compared Australian Aboriginal tear film break-up time with a European cohort and found significantly reduced tear film break-up time in the Aboriginal population.
These findings create a whole new area of research. First, are there differences in the tear film composition of ethnic groups? Second, do the differences in physical characteristics of the lids and aperture create clinical differences in lens wear response? Can clinicians predict who will have these adverse responses by paying attention to these characteristics?
As our patient populations become more diverse, we must pay more attention to these clinical issues. Are some lenses better for certain genders or ethnic groups? Are certain solutions likely to give better results than others for certain populations? Are there better tests to evaluate the tear film in different ethnic groups? We should continue this research in order to provide our patients with the best possible care.
Dr. Caffery has practiced optometry in Toronto, Canada, in a group setting dedicated to contact lens and tear film research since 1977.