Selective magnocellular damage in melanoma-associated retinopathy: comparison with congenital stationary nightblindness.

Psychophysical methods for isolating and evaluating the function of specific neural pathways are used to characterize the visual losses in patients with melanoma-associated retinopathy (MAR). These are compared with those of congenital stationary nightblindness (CSNB), a condition which displays a similar grossly abnormal ERG and loss of rod function. In MAR patients achromatic contrast sensitivity was greatly reduced in the low spatial frequency range. Stimuli chosen to isolate the magnocellular pathway were seen badly, whereas stimuli signalled primarily by the midget of the parvocellular pathway (isoluminant red/green or achromatic high spatial frequencies) were seen normally. This selective loss was not found in patients with CSNB. In MAR there is a selective loss of function subserved by magnocellular cells coupled with preservation of function subserved by the midget type 1 parvocellular cells.