Central visual defect results in loss of vision in the region of retina with the highest resolution. Due to central visual field loss, these patients experience difficulty in visual tasks such as reading and recognizing faces. Age related macular degeneration (ARMD) and juvenile macular degeneration (JMD), destroy the function of the central retina. NASA Johnson Space Center has developed an electronic remapper that can warp from one coordinate system to another on a television screen. The remapper was used in this study to redistribute visual images projecting on the macular lesion to the still functioning peripheral retina. The purpose of this study was to investigate whether remapping of reading material around the central scotomas of patients with ARMD and JMD improved reading rates. Reading rates of nonremapped words and remapped words were compared under three viewing conditions: (1) Reading without stabilization under free viewing condition, (2) Reading with image stabilization through the eye tracker, (3) Reading without image stabilization through the eye tracker.
Retinal pathology often results in visual field loss. Age related macular degeneration (ARMD) and Stargardt's disease (a congenital disease) typically affects the central macular region of the retina, resulting in visual field loss to the region of the retina with the highest resolution. Due to the central visual field losses, patients with ARMD and Stargardt's disease often experience difficulty in visual tasks, such as reading and facial recognition. NASA Johnson Space Center has developed an electronic remapper that can warp an image from one coordinate system to another on a television screen. The remapper can be used with patients with central visual field loss to redistribute information projecting off of the macular lesion (corresponding to the central scotoma) and onto the still functioning peripheral retina. The purpose of this research project was to investigate whether remapping of text around the central scotoma improved reading performance (increased reading rate) for patients with ARMD or Stargardt's disease. The subjects moved the text on the stage and read aloud random words of equal difficulty viewed on a closed circuit television screen. Reading speeds for normal and remapped text were obtained. Reading rates were determined for both free viewing and with stabilization of the position of the screen relative to the eye rotations. Results of these experiments are discussed.
Certain visual functions, such as reading, are dependent on the high resolution capability of the central visual field. When that area becomes dysfunctional the tasks become difficult or impossible. We have proposed an image warping prosthesis, in which the structure of the image that would otherwise be unseen owing to the scotoma is moved outward and onto portions of the retina that still function. Previously we used normally sighted volunteers with fixated foveation, synthetic scotomas, a limited form of image warping, and externally controlled reading saccades. Their reading rate showed improvement in a significant number of instances. In the next stage, we are prepared to use volunteers with actual, not synthesized, scotomas. The results will be used to design realistic prostheses. Different warpings may better help other visual tasks such as facial recognition. Some of the image warpings designed for reading are shown here and our rationale for considering them are given.
NASA and the University of Houston College of Optometry are examining the efficacy of image warping as a possible prosthesis for at least two forms of low vision -- maculopathy and retinitis pigmentosa. Before incurring the expense of reducing the concept to practice, one would wish to have confidence that a worthwhile improvement in visual function would result. NASA's Programmable Remapper (PR) can warp an input image onto arbitrary geometric coordinate systems at full video rate, and it has recently been upgraded to accept computer- generated video text. We have integrated the Remapper with an SRI eye tracker to simulate visual malfunction in normal observers. A reading performance test has been developed to determine if the proposed warpings yield an increase in visual function; i.e., reading speed. We describe the preliminary experimental results of this reading test with a simulated central field defect with and without remapped images.
We are investigating the possibility that a video image may productively be warped prior to presentation of a low vision patient. This could form part of a prosthesis for certain field defects. We have done preliminary quantitative studies on some notions that may be valid in calculating the image warpings. We hope the results will help make best use of time to be spent with human subjects, by guiding the selection of parameters and their range to be investigated. We liken a warping optimization to opening the largest number of spatial channels between the pixels of an input imager and resolution cells in the visual system. Some important effects are not quantified that will require human evaluation, such as local 'squashing' of the image, taken as the ratio of eigenvalues of the Jacobian of the transformation. The results indicate that the method shows quantitative promise. These results have identified some geometric transformations to evaluate further with human subjects.
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