Abstract
Abstract: :
Purpose: Central corneal thickness (CCT) can influence measured applanation intraocular pressure (IOP). The present study sought to determine whether iris color or race might represent a qualitative surrogate for adjustment of IOP. Methods: This was a prospective study of subjects 18 years of age or older. Iris color was judged as blue, green, light or dark brown. Goldmann applanation tonometry (mm Hg) and CCT (microns) measurements were assessed. CCT was measured with a Pachette 2 (DGH Technology, Inc., Exton, PA 19341). At least 10 measurements of CCT were averaged for each eye tested. Subjects were assigned to one of four groups based on race and iris color: Caucasian (blue, green, light or dark brown iris) and African–American (dark brown iris). We examined 15–18 subjects in each group for a total of 65 subjects (130 eyes). Mean CCT, IOP, and IOP corrected for CCT were compared according to iris color and race using generalized estimating equations (GEEs) to account for the intra–subject variation associated with using both eyes. P values < 0.05 were considered statistically significant. Results: Comparing CCT measurements among iris colors revealed no statistically significant differences among the three groups of Caucasians; blue (552 microns), green (553 microns), brown (563 microns). The same held true when comparing IOP and CCT–adjusted IOP, respectively, with iris color; (blue) 15.2 vs. 15.1, (green) 15.4 vs. 15.2, (brown) 14.7 vs. 14.0. When comparing CCT between Caucasians and African–Americans, CCT was significantly thinner in African–Americans (533 microns), whether evaluating all Caucasians (556 microns, p = 0.0388) or comparing only the brown–iris Caucasian group with the African–American group (563 microns vs. 533 microns, p = 0.0302). Mean measured IOP was not significantly different between Caucasians (15.1) and African–Americans (15.8), but when IOP was adjusted for CCT, African–Americans showed significantly higher CCT–adjusted IOP (16.7) than Caucasians (14.8). This is true for all Caucasians (p = 0.0486) and brown–iris Caucasians (p = 0.0206) when compared with the brown–iris African–American group. Conclusion: These results suggest that iris color is not associated with CCT, and apparently iris color does not influence measured IOP. We were unable to establish a relationship between iris color and IOP when adjusting for CCT among Caucasians. Our data show a significantly higher CCT–adjusted IOP for African–Americans than Caucasians, demonstrating a racial but not iris–color difference in CCT–corrected IOP.
Keywords: cornea: clinical science • clinical (human) or epidemiologic studies: risk factor assessment • iris