Numerical modelling of ocular accommodation process

Abstract

The ocular accommodation mechanism, as the main apparatus in the eye responsible for maintaining required vision quality when looking at objects at various distances to the eye, is one of the most vital mechanisms of the eye. Ocular accommodation is simultaneously a mechanical and an optical process and investigation of such a complex system requires advanced methods in both fields. There are at least two major processes that bring about changes in this system; the accommodation process and age-dependent deterioration of this system known as presbyopia. While the focus of this thesis is primarily on the former, the latter is also investigated. The first aim of this thesis is take advantage of nonlinear finite element method (FEM) and a purpose-made numerical ray-tracing code in order to provide a thorough understanding of the accommodation process and pertinent changes in the lens. Secondly, given the fact that the lens material possesses both mechanical and optical gradient properties, the contributions of both gradients to the accommodative response of the lens are quantified. Results show that although the lens GRIN play an important role in accommodation, it can be effectively replaced by isotropic material found through optimisation of various parameters such as the image quality. The final outcome of this thesis is a novel, optomechanical model that is shown to be able to simulate most aspects of the accommodative system and could be utilised to mimic the accommodation process and to predict outcomes of the lens refractive surgery to treat presbyopia.