Abstract
Purpose:
To understand the differences in post-lens tear exchange with soft contact lenses (CL) occurring centrally, as measured with fluorophotometry, and peripherally, as measured with a novel slit-lamp technique referred to as the out-in method.
Methods:
Eleven experienced soft CL wearers were recruited. Subjects wore 3 different CLs in randomized order: Air Optix Night and Day (N&D), Acuvue Oasys (AO) and Biofinity (BIO). Tear exchange was evaluated centrally in one eye with fluorophotometry. 2µL of 4% FITC-dextran was placed onto the posterior lens surface prior to lens insertion. Changes in fluorescence intensity in the post-lens tear film (PoLTF) were monitored to determine the tear turnover rate (TTR, %/min). Seven subjects returned for assessment of peripheral tear exchange in the same eye with the out-in method. After placing 5µL of Fluoresoft 0.35% onto the superior bulbar conjunctiva, the PoLTF at the lens periphery was monitored at the 6 o’clock position through a slit lamp biomicroscope at 20X magnification. Out-in time (OIT, sec) was recorded at the first sign of fluorescein in the PoLTF. All measurements were performed after 20-30 minutes of lens wear.
Results:
The mean TTRs determined by fluorophotometry were 12.01 %/min for N&D, 6.29 %/min for AO, and 5.21 %/min for BIO. The variance was similar between AO (6.29) and BIO (5.21), but greater for N&D (12.01). The average OITs were 167.86 sec for N&D, 75.86 sec for AO, and 135.26 sec for BIO. There were differences in variance between the CLs (N&D: 16750; AO: 1511; BIO: 4703). Based on these variance estimates, for a crossover study design the sample sizes required to detect a mean difference between lenses of 25%, with 95% confidence and 80% power, are approximately 45 subjects for TTR, and 71 subjects for OIT.
Conclusions:
The dynamics of the PoLTF is not well understood. By assessing both central and peripheral tear exchange, there is potential to gain a better understanding of tear mixing under soft CLs. Variance estimates from this study will help to define appropriate sample sizes for future crossover trials.
Keywords: 477 contact lens •
486 cornea: tears/tear film/dry eye