Delayed visual evoked response in optic neuritis.
In their 1972 study, Ian McDonald and Martin Halliday showed that visual evoked potentials can detect past episodes of optic neuritis, and thus introduced a non-invasive test to assist in the diagnosis of suspected multiple sclerosis. Halliday had been measuring evoked potentials in people with multiple sclerosis for the previous decade; meanwhile, McDonald and Tom Sears had shown that demyelinating lesions impair nerve conduction. This study found delayed evoked potentials in 19 patients with unilateral optic neuritis for as long as 5 years after their vision returned to normal, suggesting that “the technique described here provides a useful objective test for previous damage to the optic nerve.” The authors went on to find abnormal evoked potentials in patients with a previous history of optic neuritis and also in patients with no history of optic neuritis. They later proposed diagnostic criteria for multiple sclerosis that incorporated visual evoked potentials. To date, the only clinical diagnostic test that can demonstrate that a central neurological lesion is demyelinating is the cortical evoked potential, of which the pattern-evoked visual potential is by far the most sensitive and robust.