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MC Lin, A Duong, KA Polse; The Effect of Ethnicity on Soft Lens Tear Mixing . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3076.
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Purpose: We have previously reported that the post-lens tear thickness found in Asian eyes is significantly thinner than in non-Asian eyes [Lin, et al., IOVS abstracts 2001] and that the changes in corneal epithelial permeability following overnight lens wear (either with soft or rigid lenses) are more pronounced in Asian than in non-Asian eyes [Lin, et al., IOVS submitted for publication; Polse, et al., IOVS abstracts 2001]. In this study we explore the effect of ethnicity on tear mixing. Methods: Tear mixing, lens movement, and palpebral aperture size (PAS) were measured on 56 soft lens wearers (33 Asians, 23 non-Asians). Tear mixing was assessed using a scanning fluorophotometer, and vertical PAS and lens movement were measured using a computer-based image processing system. Two visits were required for each subject, and at each visit subjects were asked to wear lenses (AL-47 polymacon, 38% H2O, 14.0 mm OAD, -2.00D Power) with base curve radius (BCR) of either 7.9 or 8.7 mm. Tear mixing was estimated as time in minutes to deplete 95% of 2 µl of 4% FITC-Dextran beneath a soft lens (T95). Results: The different BCRs of a soft contact lens did not have an impact on tear mixing (p ≷ 0.05), but significantly affected the lens movement (flatter lenses have more movement in the y-axis, p < 0.05), before and after ethnicity stratification. When the data obtained from the subjects, who had PAS less than 10 mm and wore steep BCR lenses, were stratified by ethnicity, the difference in T95 between Asian (n = 21) and non-Asian (n = 12) subjects was marginally significant (23 2 vs. 29 3 minutes; p = 0.079) while lens movement in y-axis was not significant (0.5 0.1 vs. 0.3 0.1, p = 0.128). There was no difference in both lens movement and T95 between Asians and non-Asians with PAS ≷ 10 mm. Conclusion: Because small Asian eyes may have tighter upper eye lids that may in turn cause more lid-lens interaction, we speculate that tear mixing for Asians may be driven more by the transverse movement (anterior-posterior) of a soft lens than by the lateral movement (side-to-side). These data suggest that to optimize soft lens tear mixing, different lens designs may be required for Asians compared to non-Asians.
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