Commingling analyses of central corneal thickness and adjusted intraocular pressure in an older Australian population

Abstract

Purpose. To test the hypothesis that there is a major genetic determinant for central corneal thickness (CCT) in a large, population-based sample and to test whether such a determinant accounts for results previously ascribed to intraocular pressure (IOP). Methods. Measurements of IOP and CCT were collected for 1356 individuals, 49 years of age or older, participating in the Blue Mountains Eye Study (third ascertainment call). Linear regression methods were used to adjust CCT for age. IOP was adjusted for CCT. A commingling analysis was performed with a C++ program, SKUDRIVER, to investigate whether the observed CCT and IOP data, adjusted for covariates, were best described by a one-, two-, or three-distribution model. The fitted models were compared by Akaike information criterion (AIC) values. Results. Significant skewness was present in CCT and IOP distributions. The most parsimonious model for age-adjusted CCT was a single-distribution model. For IOP adjusted for CCT the most parsimonious model was a mixture of three distributions with means corresponding to 16.02, 23.36, and 35.59 mm Hg. The proportion of total IOP variance attributable to these distributions was 18.3%. Model parameters were almost identical with those in which IOP was not adjusted for CCT. None of the analyses suggested deviation from Hardy-Weinberg equilibrium. Conclusions. The findings revealed no evidence of a single major genetic determinant for CCT. Previous results suggesting the presence of a major locus for IOP do not appear to be confounded by the influence of CCT on IOP. © Association for Research in Vision and Ophthalmology.