HUMAN CONE PIGMENT KINETICS

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We will study the initial stages of vision: the capture, absorption and transduction of light energy in human cones. Capture of light in the cones is controlled by the ability of the cones to direct light from the inner segments to the outer segments which can be measured using a new optical technique, photoreceptor alignment reflectometry. Cone alignment and the shape of the alignment function will be examined in normals and in patients. The importance of variations of cone alignment within a single retinal area will be examined in a partial bleaching experiment. The relation of optical and psychophysical measures of cone alignment will be determined both to validate the optical approach and to better elucidate the optical properties controlling capture of light by the photoreceptors. The absorption of light is controlled by the optical density of the cone photopigments. To maintain a normal optical density requires the function of the cones and the retinal pigment epithelium and thus measures of photopigment optical density are good probes of the health of the outer retina. Cone photopigment kinetics and optical density will be studied using color-matching techniques which depend on the optical density of the cone photopigments. The role of variations in cone alignment in determining measurements of photopigment density and kinetics will be examined in normals and patients. Transduction of absorptions into neural signals requires proper functioning of both the inner and outer segments of the photoreceptors, including the ability to rapidly change membrane currents and to control sensitivity. We will study the temporal properties of the photoreceptors and study how the speed of the photoreceptor response changes with retinal illuminance and temporal modulation. Looking at all aspects of cone function in carefully selected diseases (ARMD, retinal detachments, central serous retinopathy, and macular holes) will allow us to study fundamental responses of the cones. We will examine the prognostic value of measures of cone photopigment optical density for progression of ARMD and recovery of retinal status, in retinal detachments, macular holes, and central serous retinopathy. We will evaluate the effect of these diseases on cone alignment.