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The effects of ocular and lens parameters on the postlens tear thickness
Meng C Lin1, Ying Q Chen, Kenneth A Polse
1School of Optometry, University of California, Berkeley, CA 94720-2020, USA. mlin@spectacle.berkeley.edu
Purpose:
To assess the effects of soft contact lens base curve radius (BCR), sex, ethnicity, central corneal curvatures, and vertical palpebral aperture size (PAS) on the postlens tear thickness (PLTT).
Methods:
The PLTT was measured using optical pachometry on 114 experienced lens wearers who were fitted with lathe-cut soft lenses (Alden 47, polymacon, 35.5% H2O, -2.00 diopter, and 14.0 mm). Each subject was randomly allocated to one lens group receiving a BCR of 7.9, 8.3, or 8.7 mm. Pachometry measurements were taken at 30 min after lens insertion. Vertical PAS and keratometry readings were measured for 94 of the 114 subjects.
Results:
The mean (95% confidence interval) PLTT was 15.7 microm (13.2-18.0 microm), 12.8 microm (10.9-14.7 microm), and 12.1 microm (10.2-14.0 microm) for the 7.9-mm, 8.3-mm, and 8.7-mm BCR groups, respectively. The differences in PLTT among the three BCR groups was significant (analysis of variance F-test; P=0.039). Post hoc testing using the Tukey honestly significant difference statistic showed that only the two extreme BCR groups (7.9 mm and 8.7 mm) were significantly different. Sex had no effect on the PLTT; however, the PLTT was significantly thinner for the Asian compared with non-Asian eyes (P=0.0001). The Asian PLTT did not vary with different soft lens BCRs. The non-Asian PLTT was thicker with lenses of the steep BCR compared with the flat BCR.
Conclusion:
These results show that the base curve radius of a soft contact lens and several ocular characteristics can affect the thickness of the postlens tear film.