The role of the multifocal visual evoked potential (mfVEP) latency in understanding optic nerve and retinal diseases.

PURPOSE: To examine the extent to which changes in the latency of the multifocal visual evoked potential (mfVEP) overlap in patients with glaucoma, recovered optic neuritis/multiple sclerosis (ON/MS), and retinal disease.
METHODS: Monocular mfVEPs were obtained for both eyes of all subjects. Latencies and amplitudes of individual mfVEP responses were measured using custom software and expressed relative to a normative group (n = 100). Recordings were obtained from patients with ON/MS (n = 12), glaucoma (n = 50), and retinal disease (n = 15), as well as control subjects (n = 50). All subjects had 24-2 visual fields; patients with retinal disease had multifocal electroretinograms (mfERGs). The patients with retinal disease were examined by a neuro-ophthalmologist to rule out optic nerve disease and, in general, had relatively subtle or unremarkable fundus examinations but abnormal mfERG amplitudes.
RESULTS: There was considerable overlap in the latencies for the patient groups for both monocular and interocular measures of mfVEP latency. This was particularly true for the patients with retinal disease and ON/MS, for whom the range of latencies was almost identical, as was the percentage of points in the field showing significant delays.
CONCLUSION: The mfVEP delays seen in patients with retinal disease are similar in magnitude and prevalence to those seen in patients with a history of ON/MS. In general, this does not present a problem when using the mfVEP in the clinic. However, a retinal problem can be confused with ON/MS or, in fact, dismissed as functional, especially if the fundus appears normal.