A cross-sectional study of corneal topography and ocular parameters in patients with myopia

Abstract

Myopia is a leading cause of visual impairment. This study aims at determining the changes in corneal asphericity, central corneal radius of curvature, anterior chamber depth, lens thickness, vitreous chamber depth, and axial length with increasing myopia. Spherical equivalent refractive error of each myopic eye was determined and grouped into three, according to increasing powers of myopia. Corneal asphericity (Q value) and central corneal radius of curvature were determined using corneal topography. Anterior chamber depth, lens thickness, vitreous chamber depth, and axial length were determined using Ascan. Changes with increasing myopia was assessed. Among 80 myopic eyes of age group 6 to 40 years, more patients were between 21 to 30 years. 60% of them were males. 60% were low myopes (<-3D), 32% were moderate myopes (-3D to -6D) and 8% were high myopes (>-6D). Mean Q values were -0.49±0.09, -0.39±0.04 and -0.28 ±0.04 for low, moderate and high myopes respectively. Mean values of apical radius of curvature of cornea were 7.66±0.07, 7.53±0.08 and 7.35±0.07 for low, moderate and high myopes respectively. Mean values of anterior chamber depth were 3.19±0.09, 3.32±0.09, 3.88±0.08; vitreous chamber depth were 19.82±0.67, 21.66±0.24, 22.66±0.45 and axial length were 23.01±0.76, 24.98±0.32,26.54±0.51 for low, moderate and high myopes respectively. A statistically significant positive correlation of increasing degrees of myopia was observed with Q value, anterior chamber depth, vitreous chamber depth and axial length; and a statistically significant negative correlation with the apical radius of curvature. In myopic eyes, a statistically significant relation exists between corneal asphericity and spherical equivalent refractive error such that, there is a tendency for the cornea to flatten less rapidly in the periphery with increasing myopia and eyes with higher levels of myopia have steeper central corneal curvature, with deep anterior and vitreous chamber and greater axial length.