Changes in Primate Crystalline Lens Volume During Simulation of Accommodation in a Lens Stretcher

Abstract

Purpose: : To determine if the lens volume changes during accommodation in a lens stretcher.

Methods: : 2 baboon lenses (3.1-9.6 years, PMT=2-24 hours) and 8 cyno lenses (1.4-9.1 years, PMT=3-50 hours) were mounted in a lens stretcher that simulates accommodation by applying radial forces (EVAS II, Ehrmann et al, Clin Exp Opt, 2008). The central cross-sectional lens shape in the unstretched state and at maximum stretch was measured using a custom-made time-domain Optical Coherence Tomography system (Uhlhorn et al, Vis Res, 2008). The lens volume was calculated using two different methods. In method 1, the lens is assumed to be an ellipsoid of revolution. In method 2, the lens contour is fit with an even Fourier cosine series (Urs et al, Vis Res, 2010) and the cross-sectional area is calculated. Volume is then calculated assuming that the lens is rotationally symmetric. The volumes in the stretched and unstretched states calculated using Methods 1 and 2 were compared using a Bland-Altman analysis.

Results: : The cosine model provided a closer fit to the actual lens shape than the elliptical model. With method 1, the lens volume decreased by (5±11) mm³ (p = 0.112). With method 2, the lens volume decreased by (2±4) mm³ (p = 0.109). The elliptical model over-predicts the unstretched, stretched and change in volume by (13±7) mm³ (p<0.001) (10±6) mm³ (p<0.001) and (3±10) mm³ (p = 0.107). The change in lens volume predicted by the cosine model for any baboon lens (95% PI) is less than 8% and not statistically significant.

Conclusions: : The ellipsoid model overestimates the volume and change in lens volume during accommodation. There are no statistically significant changes in lens volume during accommodation in the EVAS II lens stretcher.Support:NIH Grant 2R01EY14225, NIH Center Grant P30EY14801; the Australian Federal Government Cooperative Research Centres Program (Vision CRC); the Florida Lions Eye Bank; Research to Prevent Blindness; Henri and Flore Lesieur Foundation (JMP)

Keywords: accommodation • presbyopia • imaging/image analysis: non-clinical