OPTIC NEURITIS - DIFFERENTIAL LOSSES OF LUMINANCE AND CHROMATIC FUNCTION NEAR A SCOTOMA

Visual sensitivity to achromatic and chromatic stimulus flashes was de termined at sites just inside, on the boundary and just outside scotom ata in 11 patients with recovered optic neuritis. The colour of the fl ashes and the size of the steady background on which they appeared wer e such that detection was more likely to be mediated by either the lar ge-diameter, magnocellular fibres or the small-diameter parvocellular fibres of the anterior visual pathway. The spacing of the test sites r anged from 0.5 degrees to 4 degrees visual angle, depending on the sha pe and location of the scotomata. The greatest differences in sensitiv ity were between sites just inside and just outside the scotomata and in response to achromatic stimuli more likely to involve the magnocell ular fibres. This effect may be due to the size of magnocellular fibre s or to their relatively smaller numbers.