Change In Corneal 3D Shape As A Function Of Age And Ametropia

Abstract

Purpose: : To describe corneal shape as a function of age and ametropia, based on the integrated analysis of Orbscan corneal topography average models (atlases).

Methods: : A total of 5059 consenting subjects, including 2523 females and 2531 males (5 missing information), with no history of ocular disease, surgery, or recent contact lens wear, were enrolled in this study. The mean (± SEM) age was 40.4 ± 0.2 years (range: 4 to 100 years), with a spherical equivalent of -3.02 ± 0.03 D (range: -14.00 to +14.25 D) and a refractive cylinder of 0.76 ± 0.01 D (range: 0 to 6.00 D). Subjects were divided in four age groups ([0-25 years[; [25-50[; [50-74[; and [75-100[) and four ametropia groups (spherical equivalent < -4.00 D; [-4.00 to 0[; [0 to +4.00[; and ≥ +4.00 D). Orbscan II corneal topography (Bausch and Lomb, Rochester, NY) was performed on all eyes. An atlas was constructed for each group. Each atlas included a series of anterior surface elevation and curvature maps, posterior surface elevation and curvature maps, and mean pachymetry maps. Difference maps and statistics maps were generated to compare the groups. Several topography parameters were analyzed using a two-way ANOVA model.

Results: : Preliminary results revealed a significant interaction (p<0.001) between the two explanatory variables, age and ametropia, for the thinnest point value, lateral excentricity of the thinnest point with regards to the center of the topograhy, and keratometric astigmatism. No significant interaction was found between age and ametropia, but both explanatory variables, when considered independently, were found to have a significant effect on the following outcome parameters (p<0.01): maximum central keratometric value, mean power in the 0 to 3 mm radius central area, and mean power in the 3 to 5 mm annulus area (in these three zones, overall steeper anterior surface in myopic eyes and older subjects), keratometric astigmatism meridian (the steep meridian was closer to vertical in myopic eyes and younger subjects), and vertical location of the thinnest point (lower in hyperopic eyes and younger subjects).

Keywords: aging • refraction • topography