Comparative Corneal Topography and Refractive Variables in Monozygotic and Dizygotic Twins

Abstract

Abstract: : Purpose: To investigate the role of heredity in determining corneal diameters, anterior and posterior corneal shape, corneal thickness, axial length, and overall refractive errors. Methods:Thirty one monozygotic and 11 dizygotic twin pairs, aged 13 to 32 years, were enrolled in this study. Zygosity was determined by DNA isolation from buccal swab. Corneal diameter was determined by the white-to-white distance from Orbscan II topography. Corneal thickness was determined by ultrasonic pachymetry and Orbscan topography. Anterior and posterior corneal curvatures and corneal diameter were determined by Orbscan topography. Axial length was determined by A-scan biometry. Autorefractometry, manifest and cycloplegic refraction were performed to determine the refractive status. Only right eye data were analyzed by Student t test. Left eye data were comparable for all variables. Results: Mean intra-pair difference in corneal thickness was less for monozygotic than for dizygotic twins by data from ultrasonic pacymetry and by data from Orbscan topography (RE:0.41 vs 1.78 µm; p=0.003 and RE:0.63 vs 1.95 µm; p=0.002, respectively). Mean intra-pair difference in corneal diameter was less for monozygotic than for dizygotic twins (RE: 0.23 vs 1.52 mm; P=0.008). Anterior and posterior corneal topographic data show smaller mean differences among monozygotic pairs, but all the differences are not statistically significant. Mean intra-pair difference in refractive error (spherical equivalent) was less for monozygotic than for dizygotic twins (RE: 0.53 vs 1.62 D; P=0.002). Mean intra-pair difference in axial length was smaller for monozygotic pairs than for dizygotic ones (RE: 0.37 vs 0.69 mm; P=0.002) Conclusions: Corneal thickness, corneal diameter, overall refractive error and axial length have a significant genetic basis. Corneal topographic data appear to have other overriding determining factors for several of the variables studied.

Keywords: cornea: clinical science • topography • refractive surgery: corneal topography