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AB Renner, H Knau, M Neitz, J Neitz, JS Werner; Senescence of Cone Photopigment Optical Density in Genetically Characterized Dichromats . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2951.
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Purpose: To map the photopigment optical density (POD) of middle-wave (M) and long-wave-sensitive (L) cones in groups of younger (12-29 years) and older (56-83 years) genetically characterized deuteranopes and protanopes. Small field sizes were used to localize POD at 4 retinal loci. Methods: Thresholds were measured by adjusting a flickering (18 Hz) target of 0.3° dia. superimposed on a bichromatic 16° dia. background, consisting of (i) a 430 nm adapting field fixed at 11 log quanta s-1 deg-2, chosen to saturate the rods and desensitize the short-wave-sensitive cones; and (ii) a 580 nm bleaching field increased in 0.5 log unit steps from 8.0 to 11.5 log quanta s-1 deg-2, chosen to bleach the M- or L-cone photopigment. Sensitivity at 545 and 615 nm in protanopes and at 565 and 650 nm in deuteranopes were compared under bleached and unbleached conditions. Stimuli were imaged at 0 (fovea), 2, 4 and 8 deg in the temporal retina. Thresholds were modeled as a function of bleaching level. Subjects included 12 young and 21 elderly deuteranopes, and 4 young and 14 elderly protanopes. Genetic analyses identified single- and multi-gene deuteranopes and protanopes as well as their gene sequences. Results: POD decreased exponentially with retinal eccentricity, but the slope of the function did not change with age. At each retinal location, there was no significant correlation between POD and age. Single- and multi-gene dichromats did not differ significantly in their POD. Mean POD for all deuteranopes was 0.64±0.14, 0.50±0.11, 0.45±0.12 and 0.36±0.09 at 0, 2, 4 and 8 deg temporal eccentricity. Mean POD for all protanopes was 0.66±0.13, 0.55±0.10, 0.45±0.06 and 0.37±0.08 at 0, 2, 4 and 8 deg temporal eccentricity. Conclusion: There were no significant age-related changes in POD in dichromats. There were no significant differences in POD between deuteranopes and protanopes. Our findings do not support earlier reports indicating (i) a decrease in POD with age and (ii) a different amount of POD in L- and M-cones.
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