Effect of Lens Capsule Mechanical Properties on the Dioptric Response of Primate Lenses as Assessed in an ex vivo Accommodation Simulator

Abstract

Purpose: : To examine the relationship between the accommodative response of the natural lens and the force required to stretch the empty lens capsule during simulated accommodation

Methods: : Post-mortem human (n=23) and cynomolgus monkey (n=16) tissues including the lens, capsule, zonules, ciliary body, and sclera were mounted in an optomechanical lens stretching system. Starting at zero load, the segmented sclera was symmetrically stretched in a step-wise fashion from 0 to 2mm in 0.25 or 0.5mm steps at a speed of 0.1mm·s^-1. The load, lens diameter, and power were measured at each step. The lens contents were then removed through a mini-capsulorhexis using hydrodissection and aspiration or phacoemulsification. The stretching cycles were repeated on the empty capsular bag. The force required to stretch the empty lens capsular bag was compared to the power change per gram of force applied for the natural lens. The ratio of the force required to stretch the empty bag versus natural lens was compared to the change in natural lens power per gram.

Results: : The ratio of force required to stretch the empty bag versus natural lens ranged from 0.13 to 1.15 (human) and 0.69 to 1.14 (monkey). The change in natural lens power per gram ranged from -1.37D/g to 0.12D/g (human) and -3.16D/g to -1.35D/g (monkey). As the ratio of force required to stretch the empty bag versus natural lens increases, the change in natural lens power per gram also increases. When the lens capsule governs the force of accommodation (ratio=1.0), the change in power per gram is maximum.

Conclusions: : This study suggests that there is a direct relation between lens mechanical resistance and accommodative amplitude.Support: NEI grant 2R01EY14225; NSF Graduate Student Fellowship (Ziebarth); NIH 5F31EY15395 (Borja); Australian Government CRC Scheme through the Vision Cooperative Research Centre, Sydney, Australia; Florida Lions Eye Bank; AMO Inc, Santa Ana, CA; NIH center grant P30-EY014801; Research to Prevent Blindness; Henri and Flore Lesieur Foundation (JMP).

Keywords: accomodation • presbyopia • aging