Non-contact, optical measurement of lens capsule thickness ex vivo

Purpose: To design a non-contact optical system to measure lens capsule thickness in cadaver eyes. Methods: The optical system uses a 670nm laser beam delivered to a single-mode fiber coupler. The output of the fiber coupler is focused onto the tissue using an aspheric lens (NA=0.68) mounted on a motorized translation stage. Light reflected from the sample is collected by the fiber coupler and sent to a silicon photodiode connected to a power meter. Peaks in the power signal are detected when the focal point of the aspheric lens coincides with the capsule boundaries. The capsule thickness is proportional to the distance between successive peaks. Anterior and posterior lens capsule thickness measurements were performed on 13 human,10 monkey, and 34 New Zealand white rabbit lenses. The cadaver eyes were prepared for optical measurements by bonding a PMMA ring on the sclera. The posterior pole was sectioned, excess vitreous was removed, and the eye was placed on a Teflon slide. The cornea and iris were then sectioned. After the experiments, the lenses were excised, placed in 10% buffered formalin, and prepared for histology. Results: Central anterior lens capsule thickness was 9.4+/-2.9mum (human), 11.2+/-6.6mum (monkey), and 10.3+/-3.6mum (rabbit) optically and 14.9+/-1.6mum (human), 17.7+/-4.9mum (monkey), and 12.6+/-2.3mum (rabbit) histologically. The values for the central posterior capsule were 9.4+/-2.9mum (human), 6.6+/-2.5mum (monkey), and 7.9+/-2.3mum (rabbit) optically and 4.6+/-1.4mum (human), 4.5+/-1.2mum (monkey), and 5.7+/-1.7mum (rabbit) histologically. Conclusions: This study demonstrates that a non-contact optical system can successfully measure lens capsule thickness in cadaver eyes.