THE VALUE OF VISUAL EVOKED-POTENTIALS IN OPTIC NEUROPATHY OF GRAVES-DISEASE

Visual evoked potentials (VEP) were tested in patients with ophthalmopathy (OP) of Graves' disease (GD) before treatment and half-a-year and 5-7 yr after orbital decompression (7 patients) or retrobulbar irradiation (3 patients). Five patients not requiring treatment for OP and 16 healthy subjects served as controls. Treatment for OP was given on clinical grounds including decreased visual acuity (VA) indicating optic neuropathy. Before treatment VA was decreased in 5 out of 19 eyes whereas VEP were abnormal in all. The mean latency at N60 both in the operated (83.1+/-21.6 ms) and in the irradiated groups (80.9+/-7.0 ms) was significantly different from that in the untreated group (62.6+/-8.2 ms; p<0.001) and the healthy subjects (58.9+/-6.3; p<0.001). At P120 only the latency of the operated group differed significantly from that of the other groups (p<0.001). There was a relationship between the eye muscle changes seen on CT scans and the ophthalmopathy score (according to the classification of the American Thyroid Association) and the latency both at N60 and P120. A change from a V-shape to a W-shape of the waves occurred more often in the treated patients before therapy than in the other groups. Two patients had multiphase VEP in both eyes which improved after treatment. After adequate clinical response the visual acuity improved in one of the 5 patients with initially depressed VA. VEP, initially abnormal in all, improved in 7 of the 19 eyes (37%) but further deterioration was observed in 8 (42%). VEP are an objective and a more sensitive sign of optic neuropathy than VA. Improvement of VEP after therapy is remarkably infrequent even after prolonged follow-up. VEP should be always measured when signs of changes in the volume or function of the external eye muscles are present.