Overnight Corneal Swelling and Deswelling with Silicone Hydrogel Lenses

Purpose: To compare central corneal swelling (CS) after eight hours of sleep in eyes wearing 12 different silicone hydrogel (SiHy) contact lenses (CLs) and to model between-subject variability in CS and deswelling. Methods: 29 neophytes wore 12 SiHy lenses with a central transmissibility range of 31 to 211 Dk/t units (4 SiHy CLs x 3 different powers) on separate nights, in random order, and in one eye only. Central corneal thickness in both lens-wearing and no-lens contralateral eyes was measured using digital optical pachymetry before lens insertion, immediately after lens removal on waking, then 20, 40 minutes, 1, 2 and 3 hours later. Descriptive analysis and Repeated Measures ANOVA (Re-ANOVA) were conducted to verify the distribution of individual CS and average differences in CS among CL types, respectively. Simultaneous analysis of group and between-subject effects for CS vs. Dk/t as well as for deswelling vs. time was carried out using mixed modeling. The following hypotheses were tested: • Average CS in lens-wearing or in control eyes is normally distributed. • There is a correlation in average CS between lens-wearing and control eyes. • There are statistically significant differences in overall CS between the lens types. • There are constant between-subject differences in CS over the range of SiHy Dk/ts. • CS on eye-opening (intercept) can explain most of the between-subject differences in corneal deswelling. • Individual CS or deswelling response can be predicted by lens Dk/t. • Individual CS or deswelling response can be predicted by their age, sex or refractive error. Results: Distribution of corneal swelling in both lens and control eyes, both on average and for each CL, was not significantly different from a normal curve (p>0.20 for all). When averaged over CL powers, CS with lotrafilcon A was significantly higher than galyfilcon A (Re-ANOVA, p<0.001). Mixed modeling of CS vs. Dk/t showed a significant effect of Dk/t (p<0.001) only in lens-wearing eyes (and no significant effect for any other/subject-related predictors in either eyes). However, mixed modeling also showed constant between-subject differences in CS, irrespective of SiHy Dk/t differences. More than 90% of between-subject differences in corneal deswelling vs. time (in both lens-wearing and no-lens eyes) was explained by between-subject variability in CS (intercept) compared to