EXPLORATION OF PHASE STEP OPTICS

Abstract

As the global population ages, the need for optimal presbyopic solutions increases. Despite many multifocal contact lenses (CLs) marketed over the last 20 years, satisfactory vision and comfort at all distances remains elusive. ‘Phase step’ (PS) optics, a technology offering extended depth of focus (EDOF), could augment presbyopic CL correction. This thesis aimed to confirm whether PS designs can improve presbyopic near vision. The study investigated if PS design parameters can be manipulated to affect visual performance and explored influence of pupil size and spherical aberrations (SAs), on visual performance with PS designs. Furthermore, computational prediction of in vitro and in vivo on PS lens performance was assessed.

A three-modality method was employed: theoretical (computational ray-tracing analysis), in vitro (optical bench system with anatomically correct model eye), and in vivo (human clinical study). A systematic battery of PS designs were designed, fabricated on hard CL and phase plates; and trialled in vivo and in vitro.

The three-paradigm model confirms PS optics can provide presbyopes with EDOF performance. Theoretical and in vitro results demonstrated optical modified performance through lens parameter optimisation with raw visual acuity (VA) providing qualified in vivo support. Uniformity Index (UI), a novel metric quantifying stability of VA, distinguished EDOF designs as demonstrating the most stable VA.

In bifocal PS designs, the interplay between optic zone diameter (OZD) and pupil size is important. Increased pupil size in PS EDOF designs decreased near performance in the theoretical and in vivo results, with qualified in vitro support. Decentration effect correlates with the OZD-pupil size relationship. This is the first study to report SA effect on PS performance is design-dependent; generally increasing SA to the 50th SA percentile results in stable performance across object vergences for EDOF designs. Inducing moderate positive SA may aid in EDOF of these PS designs.

Good agreement was found between the theoretical and in vitro results, followed by the in vitro and in vivo and, closely by the theoretical and in vivo agreement.

Pupil size and SA affect visual performance and must be considered early in design or during prescribing. Systematic evaluation of theoretical-to-bench-to-clinical studies represents an effective and efficient framework for further development of PS solutions and potentially, future presbyopia designs.