Noncontact optical measurement of lens capsule thickness in human, monkey, and rabbit postmortem eyes

PURPOSE. To measure interspecies thickness differences in the central anterior and posterior capsules of postmortem crystalline lenses, by a technique that maintains the anatomic integrity of the lens. METHODS. Central capsule thickness was measured with a custom-built, noncontact optical system, using a focus detection technique. Anterior and posterior lens capsule thickness measurements were performed on 22 human, 29 monkey, and 34 New Zealand White rabbit intact postmortem lenses in situ. Eyes were prepared for optical measurements by bonding a PMMA ring to the sclera in the region of the ciliary body after the conjunctiva, adipose, and muscle tissues were removed. The posterior pole was removed by making a circumferential incision through the sclera approximately 7 mm posterior to the limbus. Excess vitreous was removed to expose the posterior capsule surface, and the eye assembly was placed on a Teflon slide. The cornea and iris were sectioned to expose the anterior capsule surface. After the experiments, the lenses were excised, placed in 10% buffered formalin, and prepared for histology. Lens capsule thickness was measured from the histologic slides and compared to the optical results. RESULTS. Central anterior lens capsule thickness was 8.2 ± 5.5 (human), 7.5 ± 4.4 (monkey), and 10.7 ± 4.2 (rabbit) μm optically and 12.4 ± 2.5 (human), 10.7 ± 3.7 (monkey), and 10.4 ± 2.0 (rabbit) μm histologically. Central posterior capsule thickness was 6.3 ± 2.2 (human), 5.9 ± 1.7 (monkey), and 7.8 ± 2.3 (rabbit) μm optically and 4.1 ± 1.5 (human), 3.5 ± 1.6 (monkey), and 4.7 ± 2.5 (rabbit) μm histologically. CONCLUSIONS. The central anterior and posterior lens capsule thicknesses do not appear to vary considerably among human, rabbit, and monkey eyes. There were significant differences between optical in situ measurements and histology, which indicates that histologic preparation may affect lens capsule thickness.