Measuring refractive error in the human eye using a Shack-Hartmann-based autorefractor

Abstract

The oldest and most prevalent optical system in the world is the human eye. Variations in the anatomical structure of the eye can cause errors in its optical performance, which in turn lead to errors in the overall performance of the visual system. Fortunately, these refractive errors can be measured and then corrected externally with spectacles, contact lenses, or refractive surgery. This dissertation describes the design, fabrication, and testing of a new autorefractor that can be used to objectively measure human refractive error. The new autorefractor is based on Shack-Hartmann wavefront sensing techniques and uses a novel, Fourier transform-based algorithm to estimate refractive error. The Fourier-based data analysis models the wavefront aberration as a combination of defocus and astigmatism only, expresses the simplified wavefront in terms of measurable quantities in Fourier-space, and relates the coefficients describing the wavefront to the patient's refraction. The Shack-Hartmann-based autorefractor (SHAR) is designed to be inexpensive and compact to facilitate its transition to a commercial device. It represents a significant improvement in automated clinical refraction because it can make accurate measurements of a wide range of refractive errors without relying on moving parts or the intensity of light reflected off the retina. To evaluate its performance, the SHAR was compared to the gold-standard among current commercially available autorefractors in a study of human refractive errors. The results from this limited study population suggested that the SHAR has the potential to perform at least as well as the commercial standard autorefractor.