Wavefront assessment and correction of the rat eye for two photon excitation therapies

Abstract

Photodynamic therapy (PDT) is a treatment in which light excites a photosensitive drug to produce oxygen radicals that kills nearby cells. Today, PDT’s is most commonly used application is for the destruction of cancerous tumor cells in humans, however it can also be used to treat the eye disease, age-related macular degeneration (AMD). One-photon excitation PDT treatment of AMD has not been found to successfully improve vision quality due to the revascularization in the retina which occurs post-treatment. Two-photon excitation (TPE) has been explored as an alternative because it may prevent revascularization of the retina post-treatment and provides more precise treatment localization. The rat eye has been selected as the optical model for testing TPE of a photosensitive drug, however the rat eye suffers from poor tear film quality and large optical aberrations requiring adaptive optics to improve retinal image quality and the probability of TPE. In vivo testing of the excitation of a photosensitive drug via TPE is an important step towards successful treatment of AMD in the human eye. In this thesis, the design of an adaptive optics scanning laser ophthalmoscope for two photon light delivery is outlined, retinal images and wavefront error correction of the rat eye using a Xinetics 37-channel deformable mirror are presented. The extension of a schematic rat eye model to include a contact lens and tear lens predicts improved image quality at the retina for a larger pupil size. During the course of this project, changes in refractive error and retinal image quality while using different contact lenses were observed. Based on the model and experimental observations, the use of rigid contact lenses was shown to improve retinal image quality of the rat eye and therefore the probability of TPE in the rat eye, prior to the use of adaptive optics.