A comparison of the changes in suprathreshold apparent contrast in acute and simulated optic neuritis.

A thin PVC film was used as a diffusion filter together with glass lenses in order to induce a unilateral artificial contrast sensitivity depression in controls. These artificially depressed contrast sensitivity functions were made comparable to those assessed in patients during the recovery phase of their acute unilateral optic neuritis. A technique of subjective suprathreshold contrast matching was used to determine the suprathreshold apparent contrast in patients and controls with acute and simulated optic neuritis respectively. The results showed that differences in apparent contrast between the eyes is proportional to the discrepancy in threshold contrast for high and intermediate spatial frequencies in patients with optic neuritis. For low frequencies the apparent contrast difference was independent of threshold differences. Contrast vision of controls with simulated optic neuritis did not show this frequency dependency. There was also a discrepancy in visual acuity between the two groups. Generally the control with artificially depressed contrast sensitivity functions has a letter acuity value lower than that of the optic neuritis patient with a corresponding CSF depression.