Some multiple sclerosis patients with 20/20 acuity complain of poor vision. In a previous report we accounted for this in our patient group by showing that multiple sclerosis had caused a depression of contrast sensitivity while sparing visual acuity. In this study we investigated whether some of this measured depression might be due to abnormally rapid or severe adaptation during the test procedure rather than a true permanent loss. Our finding was opposite to this supposition: adaptation was abnormally slight and/ or slow.
Depressed contrast sensitivity was not well correlated with abnormal adaptation to contrast. In patients whose contrast sensitivity losses were restricted to a band of spatial frequencies, we found no evidence that abnormalities of contrast adaptation were restricted to this same spatial frequency band. Further evidence of dissociation between abnormal contrast sensitivity and abnormal contrast adaptation is that some patients with normal contrast sensitivity showed abnormally small adaptation.
Our finding of abnormally slow or abnormally small contrast adaptation in MS patients seems to conflict with Enoch et al’s (1978) report of abnormally great adaptation after inspecting a bright stimulus. This apparent disagreement may be due to their use of prior dark adaptation, very bright adapting stimuli and patients in the acute stage of retrobulbar neuritis.