Though it has been known that color vision is mediated by three types of photoreceptors for some 200 years, there is little information about the spacing and packing arrangement of the short (S), middle (M), and long (L) wavelength sensitive cones. The spatial organization of the S cones is the best known, while little is known about the relative numbers and distribution of M and L cones. During the last grant period we established the viability of a new technique, Photopigment Transmittance Imaging, to classify cones in the fresh, excised primate retina. Full color images of the photoreceptor mosaic are acquired with a high resolution, high sensitivity CCD camera at light levels that do not bleach substantial amounts of pigment. This allows cones to be typed on the basis of the absorption spectra of their photopigments. The goal of this proposal is to use our imaging technique to map the three interleaved cone submosaics across the monkey and human retina. Such maps may eventually help 1) to understand how trichromacy is incorporated into the retina with minimal cost for spatial vision, 2) to explore the contributions of the three cone types to the post-receptoral channels that are posited from psychophysical experiments, 3) to determine the neural circuitry underlying color vision, and 4) to study the mechanisms responsible for the development of the trichromatic cone mosaic. Our preparation for the classification of cones also allows us to measure the efficiency with which the photoreceptors collect the light incident on the retina. Such measurements will allow the first comprehensive analysis of the fate of photons as they pass through the photoreceptor layer.
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