Combined corneal topographer and aberrometer based on Shack-Hartmann wavefront sensing and its clinical applications on human eyes

Purpose. Monochromatic aberrations of the eye degrade retinal image quality and lead to poor visual performance. Whole-eye aberrometry based on Shack-Hartmann wave-front sensing (SHWS) technology provides a powerful means to predict the optical performance of the eye. However, the performance of the cornea alone is not revealed by whole-eye aberrometry. Understanding its optical role is critical as the cornea contributes the major total refractive power of the eye and which can be impacted by ocular pathologies and ophthalmic appliances. My thesis project entailed (1) development, validation of a novel optical instrument that non-invasively measured the shape and aberrations of the cornea as well as aberrations of the whole-eye; (2) assessment of several fundamental clinical questions.; Methods. The instrument employed SHWS technology and a custom high numerical aperture lens strategically positioned in front of the eye to spatially resolve the corneal retro-reflection (Purkinje I). Algorithms were developed to process the recorded light from which corneal topography and refractive aberrations were derived. I rigorously validated the accuracy and repeatability of SH corneal topographer (SHCT) on both artificial and human eyes. I assessed the effect of cycloplegic drugs on human eyes, and measured tear film dynamics with two novel techniques, SHCT and virtual retro-illumination (VRI).; Results. Accuracy of the instrument on topography was under sub-micron and repeatability was within 0.065 Diopters for the higher-order refractive aberrations. The cycloplegic drugs were found have no effect on the aberration structure of neither the cornea nor whole-eye, except for an observed whole-eye hyperopic shift. This suggests that the source of accommodation must be due entirely to changes in the crystalline lens. Tear film break-up increases the corneal surface profile at the microscopic level. A novel zonal wavefront reconstructor used in conjunction with Fourier analysis revealed that tear break-up generated significant corneal high spatial frequencies. This was further supported by qualitative observations using novel virtual retro-illumination.; Conclusion. I developed, validated a new type of corneal topographer/aberrometer and two novel high resolution techniques for examining the tear dynamics. These studies illustrated the instrument's significant diagnostic benefit for clinical and research applications.