Optical measurement techniques for clinical assessment of corneal physiology

Abstract

A refined wavelength-dependent biophysical model of the relationship between corneal thickness, refractive index, and tissue hydration is presented in this dissertation. This model provides a more accurate description of the observed relationship between corneal hydration and refractive index, and highlights the need for accurate model input parameters. Particular attention is paid to the parameter for solvent refractive index, as well as the need to account for the dispersive nature of optical media in Gladstone-Dale models. In order to verify the model, a new instrument was developed to measure the thickness of the cornea during dehydration using a low-cost confocal optical system. This system has shown good performance and may be suitable for eventual clinical use. A second instrument was also designed to enable direct measurement of tissue hydration by ratiometric Raman spectroscopy at a safe laser excitation power level. This system employs a new variation of optical chopping and lock-in detection. While the system was able to measure hydration using a safe power level, the time required to make the measurement is impractical for clinical use without further development.