Age-related macular degeneration (AMD) is the leading cause of severe vision loss in the population over the age of 60. Patients with the advanced forms of AMD have central scotomas (blind spots) in their field of vision. One of the challenges of low vision intervention is to help these patients use eccentric retina when their central retina is blind. One factor in using eccentric retina effectively may be remapping of the visual cortex. ? Until the early 1990s, it was widely believed that the anatomical structure of cortical tissue did not change once it was established following early development. However, evidence has now accumulated showing rapid and dramatic cortical plasticity in adulthood following the loss of sensory input due to peripheral lesions. For example, amputation of a limb first causes the cortex previously receiving input from that limb to be silent, but shortly thereafter, this region begins to respond to stimulation of adjacent regions of the skin. It is believed that changes in the efficacy of lateral connections within cortex are responsible for this phenomenon. In the visual system, there is some evidence from cellular recordings in animals with scotomas caused by laser treatment to the retina, and from filling-in phenomena in humans, that such remapping does occur, but its relationship to visual function has not been characterized. ? In the proposed project, we will investigate changes in the cortical mapping of retinal input using functional magnetic resonance imaging (fMRI) in humans with retinal lesions caused by geographic atrophy, the advanced atrophic form of age-related macular degeneration (AMD) and a model system for studying central scotomas in general. ? The specific aims of this proposal are (1) to determine the nature and extent of cortical remapping in patients with central scotomas from AMD using fMRI, following a detailed assessment of retinal function with a scanning laser ophthalmoscope, and (2) to determine whether and how cortical remapping contributes to the development of a stable eccentric preferred retinal locus in these patients. ? ?
