BIOMECHANICAL MEASUREMENTS OF THE PORCINE LENS CAPSULE

Biomechanical measurements were carried out on capsular rings prepared from the anterior lens capsule by means of photoablation technique (e xcimer laser). The outer diameter of the metal ring used to shape the laser output was 3.2 mm and the width (wall thickness) was 100 mu m. T hickness of the lens capsule (depth of the tissue ring) was measured w ith a microscope coupled to an electronic length gauge as the differen ce in focus between latex spherules placed on the upper and lower surf aces of the capsular rings. For mechanical measurements the capsular r ings were mounted around two pins connected to a motorized micropositi oner and a force transducer, respectively, and stretched at a constant rate until rupture. Estimates of the precision of the test method wer e based on differences between measurements of paired eyes from 15 6-m onth-old pigs. Thickness of the lens capsules was 59 mu m (50-66) (med ian, range). Repeatability of a single measurement was +/- 2 mu m for a probability of 95%. Maximum strain as a percentage of the initial le ngth was 78% [68-89] with a repeatability of +/- 6%. Maximum stiffness (elastic modulus) was 23.0 N mm(-2) [10.0-31.5] with a repeatability of +/- 4.3 N mm(-2), and maximum stress was 4.4 N mm(-2) [2.8-7.7] wit h a repeatability of (.)/:1.27 N mm(-2). There were no significant dif ferences between paired eyes, but a significant variance component bet ween individuals. The experimental set-up described in this paper seem s reliable and useful for biomechanical measurements of the lens capsu le, in the physiological as well as the surgical function range. (C) 1 996 Academic Press Limited