Macular Degeneration: Ullman S

Zur D, Ben Simon GJ, Loewenstein A, Alster Y, Moisseiev J, Ullman S. · Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot, Israel. · Ophthalmic Surg Lasers Imaging. · Pubmed #15497550 No free full text.

Abstract: BACKGROUND AND OBJECTIVE: To examine a new high-resolution kinetic mapping method for scotoma in age-related macular degeneration. PATIENTS AND METHODS: A computer-based program for kinetic visual field mapping was tested in 10 healthy subjects and 14 patients with age-related macular degeneration and fixed preferred retinal locus. The stimulus was presented using a back projector on a screen located 40 cm from the subject. The findings were then compared with static results. RESULTS: Control group mapping revealed good congruency with the anatomic blind spot. Mapping of the 14 patients with age-related macular degeneration was rapid and revealed good accuracy. The average deviation of the mapping border from the anatomic scotoma border was no more than 3.1% of the scotoma radius. Static mapping of 7 of the patients with age-related macular degeneration was longer and revealed lower accuracy. CONCLUSIONS: The proposed method is more rapid, accurate, and consistent than static mapping. It allows accurate mapping of central scotoma with suprathreshold stimulus, and may be used in the future for detecting the early stages of age-related macular degeneration using subthreshold stimulus.

McManus JN, Ullman S, Gilbert CD. · Rockefeller University, 1230 York Avenue, New York, NY 10065, USA. · J Neurophysiol. · Pubmed #18199820 links to  free full text

Abstract: The ablation of afferent input results in the reorganization of sensory and motor cortices. In the primary visual cortex (V1), binocular retinal lesions deprive a corresponding cortical region [lesion projection zone (LPZ)] of visual input. Nevertheless, neurons in the LPZ regain responsiveness by shifting their receptive fields (RFs) outside the retinal lesions; this re-emergence of neural activity is paralleled by the perceptual completion of disrupted visual input in human subjects with retinal damage. To determine whether V1 reorganization can account for perceptual fill-in, we developed a neural network model that simulates the cortical remapping in V1. The model shows that RF shifts mediated by the plexus of spatial- and orientation-dependent horizontal connections in V1 can engender filling-in that is both robust and consistent with psychophysical reports of perceptual completion. Our model suggests that V1 reorganization may underlie perceptual fill-in, and it predicts spatial relationships between the original and remapped RFs that can be tested experimentally. More generally, it provides a general explanation for adaptive functional changes following CNS lesions, based on the recruitment of existing cortical connections that are involved in normal integrative mechanisms.

Zur D, Ullman S. · Department of Computer Science and Applied Mathematics, The Weizmann Institute of Science, 76100, Rehovot, Israel. · Vision Res. · Pubmed #12676241 No free full text.

Abstract: In this study we examined the perception of one- and two-dimensional patterns across central retinal scotomas, caused by age-related macular degeneration. In contrast with previous studies of disrupted visual input that used the blind spot and artificial scotomas, the current study used large central scotomas caused by physical retinal damage. Such damage is associated with atrophy and long-term cortical reorganization, and it was therefore unclear whether perceptual completion in the damaged system will be similar to that reported for artificial scotomas and the blind spot. In addition, the scotomas under study were much larger and more central than artificial scotomas for which perceptual completion has been reported. For 1-D line and grating patterns, we found perceptual completion across large central scotomas (up to radius of 7 degrees ), which is significantly beyond the range of perceptual completion in artificial scotomas. Gratings completion was better than that of a single line, and increased with bars density. The use of central scotomas allowed us to test the completion of 2-D patterns that are difficult to study in peripheral vision. We found completion of two-dimensional dot arrays over large regions that improved with pattern density and regularity. The results show that in the physically damaged system the range of perceptual completion is increased compared with artificial scotomas, they strongly support the view of an active filling-in process rather than simply ignoring the damaged location, and they show that perceptual completion of physical scotomas is likely to involve cortical processing at multiple levels. We finally discuss implications of the results to the possible use of image enhancement techniques to facilitate the perception of low-vision individuals.