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