[The state of color vision in glaucoma].
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How does the visual cortex encode color? I summarize a theory in which cortical double-opponent color neurons perform a role in color constancy and a complementary set of color-luminance neurons function to selectively correct for color fringes induced by chromatic aberration in the eye. The theory may help to resolve an ongoing debate concerning the functional properties of cortical receptive fields involved in color coding.
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PURPOSE: To objectively evaluate the clinical application of color pattern reversal visual evoked potential (CPR-VEP) on primary open angle glaucoma (POAG). METHODS: CPR-VEP and FM 100-hue test were performed in 31 eyes with POAG and 33 normal eyes. Color pattern stimulation was presented by color monitor controlled by computer program. The reversal rate of the stimulating pattern was 2 Hz and the spatial frequency of the stimulating was 0.53 cycle/degree. The color stimulating pattern include White/Black, Red/Black, Green/Black, Blue/Black, Yellow/Black, Red/Green and Blue/Yellow. RESULTS: CPR-VEP P1 latencies were obviously prolonged in POAG group in comparison with normal control group in equiluminance. All CPR-VEP P1 amplitudes, except Blue/Black P1 amplitude, show no differences between POAG group and normal control group. CONCLUSION: P1 latencies of all CPR-VEP and P1 amplitude of Blue/Black CPR-VEP were parameters for identifying acquired dyschromatopsia caused by POAG. The results showed nonselective damages in color channels and luminance channel in POAG. CPR-VEP is helpful in detecting acquired dyschromatopsia.
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We evaluated orientation discrimination in color and luminance vision using an external noise paradigm. Stimuli were spatiotemporal patches of 2D orientation noise isolating the achromatic, red-green and blue-yellow mechanisms, and matched in multiples of contrast detection threshold. We found a monotonic increase of orientation discrimination thresholds with the stimuli orientation bandwidths that is similar for both color and luminance contrasts. This dependence was fitted with two suitable models. A variance summation model suggests that internal orientation noise is significantly greater for the chromatic than for the achromatic mechanisms, while the efficiencies are similar. A gain control model of orientation tuning suggests that both chromatic and achromatic mechanisms are characterized by broadly tuned orientation detectors and that the relative chromatic deficit in orientation discrimination may only result from a slightly broader orientation tuning for the chromatic mechanisms. The moderate deficiency in chromatic orientation discrimination may account for the small differences found in shape perception between color and luminance vision.
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A commonly used method of investigating colour vision, that is, the ability of the human visual system to discriminate colours, is based on the use of isochromatic colour plates, such as those used in the Ishihara test. The present paper describes a new computer-based method of determining red/green colour vision deficiencies. The method involves the presentation of Ishihara colour plates on a computer monitor. It has been verified experimentally that, despite the differences between the spectral emission of the computer screen and the daylight reflected by the Ishihara plates, the method is capable of distinguishing between subjects with from those without colour vision deficiencies. For screening purposes, the use of a reduced number of plates is suggested. This suggestion makes use of nine instead of 14 plates, and the criterion of two incorrectly recognized plates to determine a colour vision deficiency.
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