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Amir M. Moezzi, Desmond Fonn, Natalie Hutchings, Trefford L Simpson; Mixed model analysis of corneal deswelling following overnight wear of silicone hydrogel lenses. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1491.
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© ARVO (1962-2015); The Authors (2016-present)
To model the random structure of corneal deswelling after overnight wear of silicone hydrogel (SiHy) contact lenses.
Twenty nine neophyte subjects wore twelve SiHy lenses with a central transmissibility range of 31 to 211 Dk/t units on separate nights, in random order, and in one eye only. The contra-lateral eye (no lens) served as the control. Central corneal thickness was measured using a digital optical pachometer before lens insertion, immediately after lens removal on waking, then 20, 40 minutes, 1, 2 and 3 hours later. Linear Mixed modelling was conducted (using SPSS version 22) to analyze corneal deswelling during this 3 hour period, controlling for oxygen transmissibility and subject’s age as covariates, with gender as a fixed factor using -2 Restricted Log Likelihood ratios and Hurvich and Tsai's (AICC) criteria to examine the fit.
The best fit model for corneal deswelling was a random intercept and slope model, with the average (±se) overnight corneal swelling (CCS) of 6.26±0.35 % (intercept) and average deswelling rate (slope) of -0.035±0.002 % per minute in the lens eye, and the average CCS of 3.26±0.31 % and the deswelling rate of -0.023±0.001 % per minute in the control eye. More than 99% of inter-subject variances of corneal deswelling was attributed to the intercept (p<0.0001). The inter-subject slope variance contribution was less than 1% but it was statistically significant (p<0.005).
Linear mixed modelling enabled us to analyze both the inter-subject and the fixed effects of the corneal deswelling simultaneously for the first time. Our novel analysis showed that over the 3 hour period after eye opening the inter-subject variability of corneal deswelling was mainly attributed to the inter-subject variability of the overnight corneal swelling and it was minimally impacted by the inter-subject differences in the individual deswelling rates. Despite supporting the well documented phenomenon of high inter-subject variability of the overnight CCS these novel findings suggest small differences among individual corneal deswelling rates after eye opening and irrespective of lens wear.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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