Regional threshold contrast sensitivity within the central visual field in optic neuritis.

Abstract

Contrast sensitivity was measured at nine locations within the central 10 degrees of the visual field in cases of recovered optic neuritis having varying degrees of residual deficit. A sample of 82 patches of visual field was obtained in 14 cases. Circular patches of vertically orientated sinusoidal gratings, 2.5 degrees in diameter, were used. The gratings were modulated in time at 8 Hz and the effect of spatial frequency on the threshold loss determined at each visual field location. As anticipated from what is known of visual field changes in the disorder there was considerable variation in the magnitude of the contrast threshold elevation at different locations in the visual field in any one case. The variability was more marked in cases with greater overall deficit. Three types of spatial loss were encountered. The most common was a loss which increased at higher spatial frequencies, found in 65 of the 82 patches of visual field examined. In 11 the loss was unaffected by spatial frequency and in the remaining 6 the loss was maximal at an intermediate spatial frequency. There was no instance of a loss maximal at low spatial frequencies. Overall the results indicate that sensitivity to higher spatial frequencies is more likely to be impaired following an attack of optic neuritis. In the combined results the effect of spatial frequency on the threshold elevation was statistically significant at all eccentricities (P less than 0.001). Analysis of the combined results revealed no difference in the mean contrast sensitivity loss at eccentricities of zero, 3.75 degrees or 7.5 degrees for intermediate and low spatial frequencies. There is no evidence from these results to suggest that the central foveal projection (papillomacular bundle) is more likely to be affected following an attack of optic neuritis than the projections of other eccentricities within the central 10 degrees as far as mechanisms subserving luminance vision are concerned at these spatial frequencies. Overall there was slightly greater reduction in acuity within the central 5 degrees than at 7.5 degrees eccentricity (P less than 0.05). This may be accounted for by the finding that higher spatial frequencies are more affected, rather than being related to eccentricity per se.