The electroretinogram in multiple sclerosis and demyelinating optic neuritis

The electroretinogram (ERG) to flashes of white light presented under photopic conditions and the pattern reversal visual evoked potentials (PR-VEPs) from both eyes were recorded from 14 patients with multiple sclerosis (MS) with monocular demyelinating optic neuritis (DON) and from 11 patients soon after presenting with monocular demyelinating optic neuritis alone. Fifteen and 10 normal subjects, matched for age and sex, were used as controls for each group of patients respectively. In the DON group of patients and controls the flicker following ERG (FF-ERG) to white flashes of light at 40 Hz was also recorded. Skin electrodes and averaging procedures were used for all the recordings. The PR-VEP elicited with stimulation of the affected eye was absent or abnormally delayed, and the amplitude of the 'b' wave of ERG of the affected eye was diminished in all patients. The 'b' wave latency, however, was similar in both affected and non-affected eyes and the controls. There was no difference in 'a' wave amplitude and latency between eyes of patients and normal subjects. The FF-ERG in 8 out of 10 patients with satisfactory recordings was diminished in the affected eye. These results provide neurophysiological evidence that retinal damage is not due to loss of myelin but is an early feature of demyelinating optic neuritis. This damage preferentially affects the retinal elements associated with the generation of the 'b' wave of the ERG, probably the glial cells of Müller.