ABSTRACT
The aim of the work was to study the involvement of the optic tract in both conditions by measuring the latency and amplitude of the visual evoked potentials in those patients. Subjects and Twenty patients and 10 controls were studied. Ten patients had recently diagnosed Graves' disease and 10 had recently diagnosed primary hypothyroidism. Detailed ophthalmologic assessment was performed. Pattern VEP was recorded for all subjects, each eye separately. P100 latency and amplitude were used for comparing patients and controls. Thyroid hormone levels and thyroid stimulating hormone were measured. Patients with Graves' disease had abnormally prolonged latency [P100 = 109 +/- 20 msec] as compared to controls [94 +/- 6 msec]; P < 0.05. They also had significantly lower PI00 amplitude [3.2 +/- 2.6 vs. 5.9 +/- 2.7 mV; P < 0.05]. Those with abnormal VEP [4/10 patients] had significantly higher degree of proptosis but normal visual acuity and intraocular pressure. P100 latency correlated positively with the level of T3 [r=0.79]. Patients with primary hypothyroidism had abnormally prolonged P100 latency [112 +/- 24 msec, P < 0.05. In hypothyroid patients with prolonged latency [5/10 patients], P100 correlated significantly with age [r=0.6], duration of symptoms [r=0.66] and intraocular pressure [r=0.87]. Conclusions: VEP is more sensitive as regards the detection of pre-clinical visual pathway abnormality in patients with Graves' disease than fundus or visual field examination, where prolonged latency of P100 in VEP indicates pre-clinical optic nerve involvement. In patients with hypothyroidism, prolonged latency of VEP was present in 50% of the studied cases, thus the CNS is more sensitive to thyroid hormone deficiency than to excess. Further study is needed to determine its value as a quantitative test for CNS involvement in hypothyroidism