OPTICAL AND RETINAL LIMITS TO VISUAL PERFORMANCE

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DESCRIPTION (from abstract): The long term goal of this research is to determine how optical and retinal factors affect vision. Specific aims for the next project period fall in two broad categories: retinal architecture and visual optics. Retinal architecture imposes fundamental limits on the quality of spatial vision in healthy individuals. Previous experiments indicate that visual resolution, the single most important measure of visual function used in clinical practice, is limited ultimately by the spacing of visual neurons in the retinal mosaic. In order to exploit this fact to develop useful new diagnostic tools for probing retinal disease, the principal investigator proposes to characterize the topography of resolution throughout the visual field of normal eyes. Armed with this normative standard, two clinical populations (glaucoma and amblyopia patients) will be examined for evidence of abnormally sparse sampling mosaics. Additional experiments are proposed to measure the retinal limitations to motion perception across the visual field, to compare these results to a normative map of resolution, and to compare both maps with the known topography of visual neurons in the human retina as a test of the sampling model. One major challenge to a sampling theory of visual resolution is to account for the effect on visual performance of irregularity in the sampling mosaic. To address this issue we propose a systematic investigation of the effect of irregularity on resolution and motion perception using visual targets sampled by the experimenter (who has control over the degree of irregularity) rather than by the visual system. Another challenge is to incorporate the widely accepted model of parallel pathways into the theory. According to this model of retinal architecture, the retina is not a single mosaic but a set of independent mosaics, each of which samples the retinal image concurrently for transmission to specific visual areas of the brain via sub-sets of optic nerve fibers. In order to clarify the implications of this model for spatial resolution, the principal investigator proposes to investigate whether higher centers of the visual system recombine the independent neural images carried by parallel channels, thereby increasing the effective sampling density to achieve a corresponding increase in resolution. Visual optics prevent the eye from attaining sampling-limited performance in central vision but not for peripheral vision, provided the retinal image is well focused. To determine how much optical defocus can be tolerated in the periphery before resolution begins to suffer, the principal investigator proposes a systematic study of the effect of refractive error on the resolution limit. In order to fully account for these optical effects on vision, it is important to have an accurate description of the optical quality of the retinal image. For this purpose, the principal investigator proposes to develop a novel technique for measuring the optical transfer function of the eye objectively.