Abstract
Abstract: :
Purpose:A full gamut of colors from red through green to blue is perceived by normal subjects observing a rotating Benham disc which is an achromatic stimulator consisting of a black hemifield and a white hemifield on which three black arcs are concentrically and sequentially located. When the disc is spun clockwise at rates of 5-10 HZ , the arcs appear colored from the center to the periphery: reddish, greenish and blueish respectively. Since the recent models or the subjective color phenomenon of Benham's disc are based mainly on three retinal color cell types, without considering the rod receptors input, we examined the subjective color perceptionin subjects with congenital stationary night blindness (CSNB)and compared with normals. Methods:: Four young healthy male and one female (age 18-36) with 6/6 visual acuity but severe night vision complaints revealed normal results by Ishihara color vision test, slit lamp examination and binocular funduscopy. Electroretinography(ERG) showed missing scotopic responses during dark adaptation, almost normal photopic responses, and very small b waves with preserved a waves following strong light flash stimulation. The subjects described their color perception by watching a 20 cm diameter Benham disc rotating by 6 HZ under constant illumination. The test was repeated three times with 5 min. intervals with normal pupils. Five age matched normal subjects were used for comparison. Results:The responses collected from the night blind subjects regarding their color sensations compared very well with the results of the control group Conclusion:The results showed that the subjects perceive the usual Benham colors, despite missing synaptic transmission from the retinal rods to the bipolar and ganglionar cells. It seems that the scotopic input is not essential to create the Benham chromatic illusion.
Keywords: 362 color vision • 518 photoreceptors: visual performance