Visual thresholds to low‐contrast pattern displacement, color contrast, and luminance contrast stimuli in Parkinson's disease

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Abstract
We used the computerized Moorfield Vision System to demonstrate specific increases in various perceptual visual thresholds in idiopathic Parkinson's syndrome. Fifteen patients were compared to 13 age-matched normals. Motion detection was impaired maximally (2p < 0.01 and better in two-tailed t test) at luminance contrasts of 3–7%. Stimulus was an achromatic vertical 4 cycles/°sine wave grating subtending 3° × 2°, centered 5° in the nasal field and oscillating at 5 Hz. In addition, stationary color and luminance contrast thresholds were tested with flashed display of 5° × 6° random letters, which were presented for 200 ms (color) and 50 ms (achromatic). Color discrimination was impaired in the tritan axis only (2p < 0.05 in two-tailed t test). All achromatic stimuli–luminance increments, decrements, and phase reversing stimuli–were equally well seen by patients and controls. We conclude that the dopaminergic deficit of retinal amacrine cells in Parkinson patients can be monitored by combined low-contrast and motion (displacement) stimuli. Future studies will determine if moving colored targets are more effective in discriminating patients from controls than are the achromatic gratings used in this work.