Age-related macular degeneration (ARMD) is the leading cause of visual impairment in persons 65 years of age and older. ARMD often leads to scotomas (blindspots) affecting the fovea, which result in central field loss (CFL). Many persons with CFL adopt a consistent area of the retina, outside the scotoma, that they use as a substitute for the fovea. The specific location (i.e., meridian) of this preferred retinal locus (PRL) may have a significant impact on visual function. In order to test this hypothesis, we must be able to stabilize images on the observer's retina. The goal of this proposal is to develop and validate a technique for stabilizing images in the periphery of older eyes and eyes with ARMD The """"""""gold standard"""""""" for non-contact image stabilization is the dual- Purkinje-image (DPI) eye tracker combined with a stimulus deflector. While this system has the advantage of high temporal and spatial resolution, it has several disadvantages. The most important, for our purposes, is its inability to track eyes with even mild cataract, and tracking with intra-ocular lenses is impossible. Video-based eye trackers are quite effective in cataractous eyes, and intra-ocular lenses do not present a problem. However, the temporal and spatial resolution of video-based eye trackers is greatly reduced relative to the DPI. The temporal and spatial resolution of the retinal periphery is lower than the fovea, and the high resolution required for stabilization at the fovea should not be required for stabilization in the periphery. We will test this hypothesis by comparing performance on an acuity task for targets stabilized using the DPI and stimulus deflector and with an eye movement contingent display change (EMCDC) algorithm with which we can systematically manipulate the temporal and spatial resolution of stabilization. EMCDC software stabilizes images by changing their location on a display to compensate for eye movements. We hypothesize that the temporal and spatial resolution available with a video-based eye tracker, combined with EMCDC software, will be sufficient to stabilize targets in the periphery. In addition to comparing the DPI and video-based systems directly, we will also determine the absolute change in stimulus position, relative to eye position, while images are stabilized using the EMCDC software. In this way we will know the tolerance of the retinal periphery to stimulus movement for """"""""stabilized"""""""" images. Once validated, this technique will allow us to test hypotheses regarding the specific area of PRL in patients with ARMD.
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