Measurement of Lens Capsule Thickness in Eyebank Eyes Using a Non-Contact Optical System: Feasibility

Abstract

Abstract: : Purpose: To develop an optical system for high-resolution, non-contact thickness measurement of the lens capsule in intact human eye bank eye lenses. Methods: An optical system using a focus-detection configuration was constructed. The optical system utilizes a HeNe laser beam delivered through a bidirectional 2x2 single-mode fiber coupler. The output of the sensing arm of the fiber coupler is focused on the tissue surface using a microscope objective (NA=0.6) mounted on a translation stage with 0.5µm resolution. The light reflected by the specimen is collected by the objective, refocused into the coupler, and measured using a silicon photodiode connected to the sensing arm of the fiber coupler. The detected signal is recorded as the microscope objective is translated toward the sample. Intensity maxima are detected when the focal point of the objective coincides with the capsule boundaries. The sensitivity and axial resolution of the optical system were quantified using a mirror and neutral density filters. Anterior lens capsule thickness measurements were performed on one pair of explanted eye bank eye lenses. The crystalline lens was removed from the eye after excision of the cornea and iris and placed in the optical system on a custom-made holder. The detected signal was recorded as the objective was translated in increments of 0.5µm. The geometrical thickness of the capsule was calculated by multiplying the distance between successive maxima by 1.4 (estimated value of the refractive index). Results: The optical system had an axial resolution of 3µm and a sensitivity of 30dB. The thicknesses of the central anterior lens capsule of the measured lenses were 7.0 and 7.7µm. Conclusions: This study demonstrates the feasibility of non-contact optical measurement of the capsule thickness of intact eye bank eye lenses. CR: NONE. Support: NIH grant EY14225, Florida Lions Eye Bank; Australian Cooperative Research Centre (CRC) Scheme, CRC for Eye Research and Technology, Sydney; Henri and Flore Lesieur Foundation, Palm Beach, FL.

Keywords: accommodation • microscopy: confocal/tunneling