The effect of eye closure on the post-lens tear film thickness during silicone hydrogel contact lens wear.

Abstract

The purpose of this study was to investigate the effect of eye closure on the thickness on the post-lens tear film (POLTF) during silicone hydrogel contact lens wear. Ten subjects (mean age, 30.2 +/- 8.6 years; seven males) wore balafilcon A silicone hydrogel contact lenses in both eyes during the experimental procedure (power = -2.00 D, base curve = 8.6 mm). Previously described interference techniques, based on oscillations in reflectance spectra, were used to measure the post-lens tear film. Reflectance spectra (562-1030 nm) from the front of the eye wearing a contact lens were measured at normal incidence where the thickness of the POLTF was derived from the "frequency" of the oscillations. Six baseline measures of POLTF thickness were taken, followed by eye closure in the supine position for 30 minutes. Post-lens tear film thickness measures were taken after 5 and 15 minutes of eye closure. After 30 minutes of eye closure, 1 measure of POLTF was taken every minute for an additional 15 minutes. The average baseline POLTF thickness was 2.00 +/- 0.30 microm (median, 2.00) for the 10 subjects. The average POLTF thickness decreased to 1.58 +/- 0.33 and 1.20 +/- 0.23 microm after 5 and 15 minutes of eye closure, respectively (repeated measures ANOVA, F = 42.18, P < 0.0001). Only 5 of 60 POLTF thickness estimates were obtained for the first 6 minutes following completion of 30 minutes of eye closure, indicating that the POLTF may be too thin (i.e., <1 microm) to measure using this method. However, there was a significant increase in POLTF thickness for 15 minutes after prolonged eye closure (mixed modeling regression, thickness = 0.85 + 0.07 x time after eye opening; P < 0.0001). The POLTF thickness is rapidly reduced by eye closure during contact lens wear. After 30 minutes of eye closure, the POLTF thickness may be reduced to values less than 1 microm for the first several minutes after opening the eyes.