The separation of parallel visual systems by disease processes

to investigate psychophysics and electrophysiology in disease states with altered retinal function.

determination of colour and luminance contrast sensitivity functions using computer controlled VDUs: recording of flash and pattern ERGs to short and long flashes of coloured lights under differing conditions of light adaptation: recording of pattern ERG.

In melanoma-associated retinopathy (MAR) low spatial frequency temporal flicker loss occurs for achromatic Gaussians, but colour Gaussians are seen normally. Low spatial frequency luminance contrast sensitivity and motion losses are severe while red-green gratings are seen normally. In Cuban Tropical Amblyopia, achromatic luminance contrast sensitivity may be normal, in the presence of considerable losses of colour vision, to spatial frequencies as high as 32 c/degree. There are supernormal cone ERGs.

these 2 conditions represent highly selective loss of 'M' and 'P' pathways respectively. Almost the entire 'bell shaped curve' normally represents M activity. In CTA, there may be a selective loss of the receptive field surrounds of P ganglion cells.