Use of large diameter rigid contact lenses as a model for orthokeratology optical treatment effect.

Both animal and human studies have demonstrated that the peripheral retina influences central refractive error development. It is hypothesised that peripheral hyperopic defocus may act as a strong stimulus for axial eye elongation. However, conflicting reports have been published suggesting no influence of peripheral refraction on human central refractive error development. Therefore, the role of the peripheral retina on myopia development in human eyes is yet to be understood. Interestingly, optical treatments that have been developed to induce peripheral myopic defocus using peripheral add power have been found to show some myopia control effects, indicating peripheral refraction may play a role in myopia development. Currently, orthokeratology (OK) is considered as the most effective optical treatment for myopia control. It is hypothesised that mid-peripheral corneal steepening may induce peripheral myopic defocus changes in myopic eyes treated with conventional OK lenses. However, there is large variability in myopia control outcomes with OK treatment which may be due to differences in ocular shape and peripheral refraction among individuals. Attempts to individualise peripheral optical defocus changes through manipulation of anterior corneal shape using OK lens designs are tedious and time consuming. Instead of manipulating the anterior corneal shape, this thesis aims to use large diameter (LD) rigid lenses as a novel optical model to induce peripheral defocus changes by anterior contact lens surface manipulations to mimic the OK optical treatment effect. However, before manipulating the front surface profile of these LD contact lenses, there was a need to understand the fitting aspects of LD contact lenses.To investigate the fitting aspects of LD contact lenses, the CASIA swept source (SS) anterior segment optical coherence tomographer (OCT) was used extensively in the research studies reported in this thesis. It has been reported previously that OCT instrumen