Novel Approach to Ocular Photoscreening

Photoscreening is a technique that is typically applied in mass pediatric vision screening due to advantage of its objective, binocular, and cost-effective nature. Through the retinal reflex image, ocular alignment and refractive status are evaluated. In the USA, this method has screened millions of preschool children in the past years. Nevertheless, the efficiency of the screening has been contentious. In this dissertation, the technique is reviewed and reexamined. Revisions of photoscreening technique are developed to detect and quantify strabismus, refractive errors, and high-order ocular aberrations. These new optical designs overcome traditional design deficiencies in three areas:

First, a Dynamic Hirschberg Test is conducted to detect strabismus. The test begins with both eyes following a moving fixation target under binocular viewing, and during the test each eye is designed to be unconscientiously occluded which forces refixation in strabismus subjects and reveals latent strabismus. Photoscreening images taken under monocular viewing are used to calculate deviations from the expected binocular eye movement path. A significant eye movement deviation from binocular to monocular viewing indicates the presence of strabismus.

Second, a novel binocular adaptive photorefraction (APR) approach is developed to characterize the retinal reflex intensity profile according to the eye's refractive state. This approach calculates the retinal reflex profile by integrating the retinal reflex intensity from a coaxial and several eccentric photorefraction images. Theoretical simulations evaluate the influence from several human factors. An experimental APR device is constructed with 21 light sources to increase the spherical refraction detection range. The additional light source angular meridians detect astigmatism. The experimentally measured distribution is characterized into relevant parameters to describe the ocular refraction state.

Last, the APR design is further applied to detect vision problems that suffer from high-order aberrations (e.g. cataracts, dry eye, keratoconus). A monocular prototype APR device is constructed with coaxial and eccentric light sources to acquire 13 monocular photorefraction images. Light sources projected inside and along the camera aperture improve the detection sensitivity. The acquired reflex images are then decomposed into Zernike polynomials, and the complex reflex patterns are analyzed using the Zernike coefficient magnitudes.