Adaptive Optical Devices in Vision Science

Abstract

In this thesis we investigate the use of adaptive optical devices in three different areas of vision science. These areas are defocus perception, retinal imaging and severe vision loss.

Birefringent material has been utilised to produce optical components that can control the angle of refraction of incident light. Using a ferroelectric liquid crystal (FLC) the orientation of linear polarised light can be controlled. This provides us with the ability to switch between the two refractive indices of birefringent materials at very high speeds.

A focus switchable lens (FSL) has been made from barium borate (BBO), and a ferroelectric liquid crystal to switch between equal and opposite defocus levels to determine the optimum focus correction by making use of the human eye's sensitivity to flicker. Flicker simulation result indicate that there is a high dependence of flicker sensitivity to the flicker frequency. High spatial frequencies also increased the ability to perceive small defocus shifts. Promising results have been obtained showing a person is able to find a point of equal defocus using flicker more accurately than they would be able to find perfect focus.

The same focus switching lens system has the ability to produce fast focus switching cameras. Its potential has been analysed for the use in retinal cameras to ease the process of obtaining good quality images of the optic nerve and providing such cameras with the ability to switch focus within the depth of the optic nerve head at high speeds. Simulation results showed that two FSLs positioned within the zoom system of the imaging arm are able to create focal point shifts of very small amounts.

Finally, collaborative research has been conducted in the use of a birefringent prism in conjunction with an FLC to create image jitter that can enhance visual performance in people with severe visual impairment. Image jitter created on-screen and via an optical system was tested. Patients were able to increase their reading speed and improve their ability to discriminate between happy and sad faces.