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KA Polse, MC Lin, S Han; Wearing Time Affects Post-lens Tear Thickness Under a Soft Contact Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):970.
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Purpose: To measure the time effects on the post-lens tear thickness (PLTT) of standard disposable and silicon-hydrogel soft contact lenses. Methods: The PLTT was measured using optical pachometry1 at 1, 5, 10, 15, 30, and 60 min., and then every 90 min. thereafter, over a period of 7 hrs. of lens wear. A total of 11 experienced soft lens wearers (6 males, 5 females) participated in the study. Contact lens type was randomized for the first visit; the other lens type was worn on the same eye at the second visit. Results: The mean 1 SD of the central PLTT measured at 10 intervals over a 7-hr. wearing period is shown in the graph below. For the etafilcon-A lens, the PLTT increases about 4µm over the first 30 min. and then stabilizes at about 12µm for the remainder of the wearing period. However, the PLTT for the lotrafilcon-A lens shows a relatively steady decrease during the first 60 min. of wear and then stabilizes at about 2µm for the remaining 6 hrs. of wear. After 60 min. the PLTT is significantly greater for the etafilcon-A lenses (p < 0.001). View OriginalDownload SlideView OriginalDownload Slide Conclusion: The average PLTT under etafilcon-A lenses is thicker than under the lotrafilcon-A lenses. After 60 min., the PLTT of both lens types appears to remain stable; however, the PLTT for the silicon-hydrogel lens is relatively thin. As PLTT is directly related to tear mixing efficiency2, it may be important to find strategies for increasing the PLTT under silicon-hydrogel lenses. Refs: 1) Lin, et al., Measurement of Post-lens Tear Thickness, IOVS 1999;40. 2) Creech, et al. Dispersive Mixing in the Posterior Tear Film under a Soft Contact Lens. Ind Eng Chem Res 2001;40.
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