Age-Related Changes in Lens Power, Thickness and Surface Curvatures with Stretching Force during Simulated Accommodation in Baboons

Abstract

Purpose: : To quantify the age dependence of changes in lens power, thickness and surface curvatures with respect to stretching forces during simulated accommodation in hamadryas baboon lenses.

Methods: : A lens stretching system (Ehrmann et al, Clin Exp Opt, 2008) was used to simulate accommodation on 22 hamadryas baboon lenses from 21 donors (1.8-24.7 years, PMT 18.5±12.5 hours). The tissue was stretched in a step-wise fashion radially from 0 to 2.5 mm in 0.25 mm incremental steps. The power and shape of the lens, and the force exerted to stretch the lens was recorded at each step. The lens cross-sectional profile was imaged with a custom designed time-domain optical coherence tomography (OCT) system (Uhlhorn et al, Vis Res, 2008). Optical distortions were corrected using published methods (Borja et al, Biomedical. Opt. Exp, 2010). The anterior and corrected posterior lens surfaces were fit over the central 3 mm optical zone with a spherical fit to calculate the anterior and posterior surface curvatures. A linear regression was performed on the changes in lens power, thickness, anterior and posterior surface curvatures as a function of force during stretching to obtain the corresponding slopes for each lens. Linear regressions were then performed on the lens power-force (in D/g), lens thickness-force (in mm/g), anterior surface curvature-force (in mm^-1/g) and posterior surface curvature-force (in mm^-1/g) slopes as a function of age to determine the age-dependency.

Results: : There is a significant age-dependent trend in the lens power-force slope (0.3694 D/g/years, p < 0.001), lens thickness-force slope (0.0106 mm/g/years, p < 0.001), anterior surface curvature-force slope (0.00127 mm^-1/g/years, p < 0.001), posterior surface curvature-force slope (0.0009 mm^-1/g/years, p < 0.001). The lens power-force, lens thickness-force, anterior surface curvature-force and posterior surface curvature-force slope increase with age.

Conclusions: : For a given stretching force applied to a lens, a smaller power and shape change is produced in older baboon lenses than in younger lenses.

Keywords: accommodation • presbyopia