A recently developed surgical procedure, limbal stem cell replacement, now permits corneal replacement in many patients who were previously ineligible for surgery. Many of these patients have suffered long-term visual deprivation, thus providing an extremely rare opportunity to examine how visual function is dependent on experience. We will study: (1) The neural site of deprivation-based acuity loss. We will partition the sites of deprivation-based resolution loss between the optics, lateral geniculate nucleus, and primary and secondary visual areas, using a conjunction of the psychophysical (external) contrast sensitivity function, the interferometric contrast sensitivity function and the neural response function within the lateral geniculate nucleus, striate, and extrastriate visual areas measured using functional magnetic resonance imaging (fMRI). (2) Behavioral losses as a function of deprivation. Preliminary data suggests that long-term visual deprivation also results in deficits in higher-level visual processes, such as the processing of configural form, objects, and faces. In contrast, color and motion processing seems relatively unaffected by long periods of deprivation. We will test our patients on a wide range of behavioral tasks to see how the effects of deprivation interact with task. (3) The neural site of behavioral losses. We will define, based on both anatomical and functional criteria, a wide range of cortical visual areas, including the lateral geniculate nucleus, areas V1-V4, motion area MT+ and regions in the fusiform lingual gyd thought to be responsible for face and object processing. We will compare patients' behavioral performance to the size and sensitivity of these visual areas. Besides being a unique opportunity to study the effects of deprivation on the human visual system, this research should provide patients who are undergoing sight recovery procedures with information as to what sort of sight they should expect postoperatively. Stem cell replacement is a major operation that is becoming more and more common, and other techniques for sight restoration, such as retinal prostheses, have shown remarkable progress in recent years. It is important that patients are given an accurate estimation of risks and benefits when being given the option of undergoing sight-recovery procedures. ? ?
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