Multiple sclerosis can cause visual processing deficits specific to texture-defined form.

We performed the following tests in 25 patients with multiple sclerosis (MS) and 25 age-matched control subjects: recognition of texture-defined (TD) letters; recognition of motion-defined (MD) letters; and recognition of luminance-defined (LD) letters of 96% and 11% contrasts. Six patients with normal visual acuity were abnormal on recognizing TD letters, of whom one gave normal results on all other tests. Eleven patients were abnormal on MD letter recognition, of whom four gave normal results on all other tests. Visual acuity for letters of 11% contrast were abnormally low in seven patients, of whom two gave normal results on all other tests. We conclude that the neural mechanisms underlying recognition of TD, MD, and low-contrast LD letters in subjects with normal visual acuity are sufficiently different that they can be differentially damaged by MS. Therefore, TD, MD, and LD letter tests provide complementary information. We suggest that the detection of TD letters can be disrupted by demyelination of long-range horizontal connections between orientation-tuned neurons in the striate cortex.