Development of an automated optical system for corneal birefringence characterization

Abstract

The aim of this project was the qualitative and quantitative characterization of the variations in the corneal birefringence in the rabbit eye through the design and development of an automated optical setup. The results will be used for the development of a non-invasive optical polarimetric glucose sensor. In order to fully understand the various features that needed to be incorporated in the automated optical system, the initial stage of the research was spent in building and testing the manual optical system for Mueller matrix computation. The manual system was first characterized with a material of known birefringence, namely a 1/4 wave plate. The Mueller elements for different sets of rabbit eyes were then analyzed to determine the variation of intensities across the rabbit cornea for different Mueller elements. In addition the fast axis of the excised rabbit cornea was also determined. Using a manual system required 2-2 1/2 hours to collect the Mueller matrix images and increased risk of error, which was approximately 30%. Therefore, such a system for the end application of determining the Mueller matrix of the rabbit cornea in vivo was unsuitable. An automated system that overcame all the drawbacks of the manual system was required and hence designed and modeled. The operation of the automated system was verified by testing a sample whose Mueller matrix was known theoretically, namely the 1/4 wave retarder with its fast axis at different orientations. The results were in agreement with the theoretical values with an overall error percentage between the theoretical and the experimental of less than 15%. The time for collecting the Mueller matrix of a sample was a few minutes. Also, the data collected with the automated system was highly repeatable with a standard error percentage of less than 10%. Experiments with the automated optical system were conducted to determine the Mueller matrices of glucose at different concentrations and to determine the Mueller matrix of the cornea in an ex vivo rabbit eye.