Spatio-Temporal Visual Response for Ocular Correction of Higher-Order Aberrations

Abstract

With the development of control aberration using adaptive optics (AO), particular emphasis has been given recently to the impact of higher-order aberrations (HOAs) on visual performance, with a view to improved refractive corrections, for example using customised intra-ocular lenses (IOLs). However, to date most studies have used simple static visual tasks, whereas more complex realistic tasks are required to reveal the spatio-temporal complexity of the human visual response. In this Thesis, we start by performing an introductory study of spherical versus aspheric IOL design, in which the need for exact ray-tracing is emphasised, demonstrating the significance of higher-order aberrations in post-operative surgery correction as well as in realistic eye models. Turning to visual characterization of HOAs and their predictability by metrics, the development of a new adaptive optics vision simulator is addressed. We describe the design, construction and testing of this AO system. In an experiment in which we correct the natural aberrations of the eye, and introduce fixed amounts of pure Seidel aberrations, we measure how the pyschophysical visual acuity changes and compare the results with metrics. By combining the aberration control of this new system with computational manipulations of the spatio-temporal stimulation based on advanced attentional paradigms, we show that the perceived degradation by HOAs is a distinctly sensitive response that varies with the nature of the stimulation and the spatio-temporal pathway visually excited. This study concludes that aberrations not only affect absolute visual performance, but also may adjust the mediative mechanism that articulates spatial and temporal visual representations. This novel result has important consequences for the expansion and assessment of customized refractive correction, and provides a new method for understanding cortical plasticity and visual function.