Geunyoung Yoon - US grants

DESCRIPTION (provided by applicant): Wavefront aberrations in the eye's optics degrade vision. These aberrations, including many higher order aberrations that are not corrected by conventional spectacles, are especially severe in patients with keratoconus and in patients who have had penetrating keratoplasty. Accurate measurement and correction of these higher order aberrations could result in substantial improvements in vision. However, little wave aberration data can be obtained from patients with these conditions, primarily because existing wavefront sensors have too small a dynamic range to measure the large aberrations in these eyes. Moreover, even if measurements were available, there are few available therapeutic alternatives. The research objectives of this bioengineering research project are to develop a robust wavefront sensor, with a large dynamic range, that will reliably diagnose the wave aberrations in highly aberrated eyes, and to develop a customized contact lens that can compensate for most of these aberrations. The key to expanding the dynamic range of the wavefront sensor is the use of a translational plate that increases spacing between wavefront sensing spots. The key to developing the contact lens is the use of high-power laser ablation of the contact lens based on the measurements with the wavefront sensor.

DESCRIPTION (provided by applicant): In eyes with prolonged visual deprivation induced by the abnormally large optical defects such as aberrations, the actual visual performance after precise correction of remaining aberrations is significantly poorer than that predicted from optical theory and that measured in normal eyes. This unexplained vision loss suggests that the degraded image quality received by the eyes alters neural processing of images formed on the retina, which plays an important role in determining perceived visual quality. We hypothesize that the post-correction functional measurements on a given patient are biased by long-term neural adaptation to the poor retinal image quality that the patient may have progressively experienced before correction. We will test this hypothesis using a corneal disease, keratoconus as a model of long-term visual adaptation. The visual system of this unique patient group developed normally but, during adulthood, has gradually experienced severely degraded image quality by the large magnitude of aberrations for a prolonged period of time. The proposed project implements the latest tools and advances in human optics research to investigate (1) the mechanisms underlying long-term neural adaptation to degraded optical quality of the eye and (2) neural plasticity resulting from improved optics and/or visual training paradigms. We will use two innovative advanced correction tools: an adaptive optics vision simulator and a customized scleral lens for short-term and long-term precise aberration correction, respectively. Aim 1 is designed to investigate the mechanisms that underlie long-term neural adaptation to the optically degraded retinal image quality and their impact on neural processing of image quality by (1.1) testing the hypothesis that the neural system is capable to compensate for losses in image quality due to the ocular aberration through long-term adaptation to phase spectra using broadband stimuli, acuity letters and natural images (1.2) characterizing long-term adaptation induced-changes in the key properties of basic spatial vision mechanisms using narrow band visual stimuli i.e. gratings and (1.3) examining the effects of long-term neural adaptation on the two eyes being integrated with regard to the monocular functions including visual acuity, contrast perception at and above threshold before and after aberration correction. Aim 2 will assess the extent to which plasticity that occurs during long-term adaptation is reversible and what mechanistic changes underlie this reversal once aberration-free image quality is achieved in KC eyes. (2.1) We will first quantify the time course of passive neural re-adaptation to improved ocular optics achieved by wearing customized aberration correcting scleral lens daily. We will also apply different visual training paradigms based on (2.2) narrow (single spatial frequency gratings) and (2.3) broad (natural images) band visual stimuli to differentiate different mechanisms of neural plasticity and to test the hypothesis that visual performance can further be improved by the visual training. Binocular transfer of the monocular neural manipulation through visual training effects will also be examined.

It is well known that the optics of the human eye limit many aspects of visual function including visual acuity and contrast sensitivity. Less is known about how the eyes? optics affect binocular vision. There is clear evidence that optics affect both stereopsis and binocular summation. Interestingly, inter-ocular differences in optics impede some aspects of binocular function while facilitating others. Moreover, our previous studies found that in eyes with prolonged visual deprivation induced by the abnormally large optical defects such as aberrations, neural processing of both contrast and phase of retinal images are altered. Our preliminary studies have also shown that binocular visual functions e.g. binocular summation, subjective image quality and stereo-resolution are determined by strong binocular neural interaction with the optical profiles of the two eyes. We are now ready to distinguish contributions of optical and neural factors to binocular vision, including in patients with the corneal disease called keratoconus (KC). With this unique condition, a normally developed visual system suffers optical degradation in adulthood, thus providing opportunity to study adaptation to induced optical aberrations on binocular visual function. We will utilize innovative advanced correction tools, a binocular adaptive optics vision simulator and a customized scleral lens for short-term and long-term precise aberration correction/manipulation to study (1) the effects of optics on binocular combination of dissimilar monocular images, (2) contributions of binocular optics to human stereopsis and (3) binocular neural plasticity stimulated by improved optics and binocular perceptual learning. Aim 1 is designed to investigate the mechanisms that underlie binocular combination of dissimilar retinal images induced by inter-ocular differences in the eye?s optics. This is achieved by testing the hypothesis that the human visual system can achieve binocular combination of neural signals arising from left- and right-eye images in a manner that enhances the global binocular image quality via interocular processes operating over local regions of visual space in an eye-selective manner (1.1), by characterizing changes in sensory dominance induced by long- term adaptation to eye?s optics (1.2) and by testing the hypothesis that dissimilar monocular aberrations alter phase perception of a broadband stimulus differently in the two eyes, resulting in reduced binocular advantages and inter- ocular inhibition in some severe cases. Aim 2 is to investigate both optical and neural factors including aberrations, fixational eye movements and long-term neural adaptation in human stereopsis. Aim 3 will assess the extent to which binocular plasticity that occurs during long-term adaptation is reversible and what mechanistic changes underlie this reversal once aberration-free image quality in the two eyes is achieved in KC eyes. Successful completion of these specific aims will produce fundamental insights into human binocular vision, specifically the relationship between ocular optics and the binocular neural adaptive process.