Electrophysiological Studies in Thyroid Associated Orbitopathy: A Systematic Review

Dysthyroid optic neuropathy (DON) is the commonest cause of blindness in thyroid associated orbitopathy (TAO). While diagnosis remains clinical, objective tests for eyes with early or equivocal findings are lacking. Various electrophysiological studies (EPS) have been reported, yet the types and parameters useful for DON remain inconclusive. We performed a systematic literature search in MEDLINE, EMBASE and the Cochrane databases via the OVID platform up to August 20, 2017. 437 records were identified for screening and 16 original studies (1327 eyes, 787 patients) were eligible for review. Pattern visual evoked potential (pVEP) was the most frequently studied EPS. Eyes of TAO patients with DON showed delayed P100 latencies, decreased P100 amplitudes or delayed N75 latencies during pVEP, compared to those without or healthy controls. Due to study heterogeneity, no quantitative analysis was possible. This review highlights the most common type (pVEP) and useful parameters (P100 latency and amplitude) of EPS, and supports further research on them using standardized testing conditions.