The Role of the Flash Visual Evoked Potential in Evaluating Visual Function in Patients with Indirect Traumatic Optic Neuropathy

PURPOSE: To assess the value of the flash visual evoked potential (FVEP) in determining final visual prognosis in patients with indirect traumatic optic neuropathy (TON). SUBJECTS AND METHODS: We included 30 patients diagnosed with indirect TON. Within one week of the onset of the trauma, visual acuity was recorded, pupillary reactions were assessed, FVEP was performed in both eyes. The amplitudes (N1p1 and N2P2) and the latency of P2 for each eye were recorded and amplitude ratio of N2P2 between the affected and normal eye was calculated. In follow-up visits, the cases underwent a complete ophthalmic examination, assessment of visual acuity, pupillary reaction, and FVEP. RESULTS: The study included 22 males (73.3%) and 8 females (26.7%). The right eye was involved in 16 patients (53.3%) and left eye was involved in 14 cases (46.7%). According to the findings of FVEP, there was a direct correlation between final visual acuity and initial amplitude of N1p1 and N2P2 and negative correlation with latency of P2 wave. In 20 patients in whom the N1P1 and N2P2 amplitude was within the normal range and amplitude ratio of N2P2 of normal and fellow eye was at least 0.5 and the P2 implicit time was less than 140 ms, they achieved better visual outcome and visual acuity improved in the affected eye. In other 10 patients in whom the N1P1 and N2P2 amplitude was below normal range and the N2P2 amplitude ratio between the normal and the affected eye was less than 0.5 and the P2 implicit time was more than 140 ms, the visual acuity in the affected eye was less than 0.01 and these patients achieved less or no improvement in their visual function. CONCLUSION: Cases with TON usually present with severe loss of vision. FVEP is highly predictive of final visual outcome in patients having indirect TON given that the other eye is normal to be used as the patients’ internal control. More studies are needed to confirm these results.