Delayed visual perception and delayed visual evoked potentials in the spinal form of multiple sclerosis and in retrobulbar neuritis

Abstract

(1) We have used both subjective and evoked potential tests to study cases of multiple sclerosis with no history of retrobulbar neuritis (spinal patients) and compared them with patients with multiple sclerosis who had experienced an attack of retrobulbar neuritis (RBN). We measured the delay of steady-state evoked potentials (EPs) elicited by flicker in the medium-frequency (13-25 c/s) range, by flicker in the high-frequency (30-60 c/s) range, and by pattern-reversal. We also measured the delay in seeing (perceiving) both an increase of light intensity and a decrease of light intensity. (2) The difference between perceptual delays for the left and right eyes (D s) was abnormal when retrobulbar neuritis affected only one eye (22/22 patients) even when acuity and discs were normal. It might be supposed that this perceptual test would be ineffective when both eyes were affected by retrobulbar neuritis. However, the value of D was abnormal in cases of bilateral retrobulbar neuritis (5/5 patients). Probably the principal reason is that demyelination was patchy in the patients studied. For this same reason the difference between perceptual delays for two sites in the visual field (T s) may also be abnormal. In principle the perceptual delay test can be effective even when both eyes are similarly delayed: abnormal values of T were recorded in 5 spinal patients for whom D was normal. (3) Perceptual delays were measured for an extended group of 19 patients suffering from spinal multiple sclerosis. Taking both D and T into account, the perceptual delay test alone picked out 12/19 spinal patients. The perceptual delay test has the advantage over EP tests that it can detect islands of demyelination as small as 3 degrees diameter, and the apparatus is cheap and straightforward to use. (4) Thirteen patients with spinal multiple sclerosis, including 6 with no ocular signs or symptoms, were examined with a battery of two evoked potential and one perceptual test. Ten patients had clearly abnormal visual delays. Results for the remaining 3 were equivocal. Delay tests can reveal visual damage in most patients who have not experienced an attack of RBN as well as in practically all patients who have experienced an attack. (5) Correlations between the results of the various tests were different in spinal patients and in multiple sclerosis patients who had experienced an attack of retrobulbar neuritis. Flicker EPs, pattern EPs and visual perception were all delayed in every RBN patient, whereas for spinal patients different tests could pick up different patients. Flicker EPs picked up 5/13 spinal patients, pattern EPs 6/13, perceptual delay (D) picked up 4/13 and perceptual delay T picked up 7/13. (6) Delay tests divided spinal multiple sclerosis patients into two fairly distinct groups. In one group pattern EPs and perception were delayed; in the other group flicker EPs were delayed. This grouping corresponded to a clinical distinction between long-standing patients with visual signs and recent patients without visual signs...