THE STUDY OF VISUAL-EVOKED POTENTIALS IN PATIENTS WITH THYROID-ASSOCIATED OPHTHALMOPATHY IDENTIFIES ASYMPTOMATIC OPTIC-NERVE INVOLVEMENT

In the present study we have recorded visual evoked cortical potential s (VECP) in 88 patients affected by autoimmune thyroid disease and thy roid-associated ophthalmopathy (TAO) without clinical signs of optic n europathy. At the time of ophthalmological examination, 37 of these pa tients were hyperthyroid, 41 were euthyroid, and 8 were hypothyroid; 2 were not assessed. Twenty-nine normal subjects served as controls. We performed pattern reversal visual stimulation and recorded the amplit ude and latency of the cortical electric response at 100 ms (P100 wave ). There were no differences in the mean P100 amplitude of TAO patient s and normal subjects. The mean P100 latency in patients was 105.6 +/- 0.5 ms, significantly higher than that in normal subjects (102.0 +/- 0.5 ms; P < 0.00003). Latency in euthyroid patients did not differ fro m that in either hypo- or hyperthyroid patients. The VECP test was pos itive (latency, greater than or equal to 110.0 ms) in 21 (23.8%) TAO p atients. In patients with proptosis greater than 21 mm, latency was 10 6.7 +/- 0.7 ms, significantly higher than that in patients with normal Hertel measurements (104.3 +/- 0.6 ms; P < 0.01). Latency was not inc reased in patients with acute inflammatory signs compared to those wit h inactive eye disease and in patients with altered extrinsic motility . In patients with an abnormal visual field study, the mean latency wa s 110.3 +/- 1.5 ms, significantly higher than that in patients with a normal visual field (104.7 +/- 0.4; by t test, P < 0.000003). In concl usion, we observed a prolongation of the latency of the evoked cortica l response in patients with TAO without subjective visual complaints a nd without optic nerve compression. We believe that the study of VECP in TAO is complementary to the study of the visual field in identifyin g early optic nerve dysfunction in the absence of decreased visual acu ity.