Asymptomatic Fellow Eye Involvement in Nonarteritic Anterior Ischemic Optic Neuropathy

BACKGROUND: Sequential nonarteritic anterior ischemic optic neuropathy (NAION) has been reported to occur in approximately 15% of patients within 5 years of the first episode. However, the incidence of presumed previous asymptomatic episode of NAION in fellow eye of patients presenting with acute NAION has not been previously reported. We reviewed charts of patients with acute NAION seen over a 5-year period to determine the frequency of visual field (VF) defect in the fellow eye secondary to presumed previous asymptomatic episode of NAION. METHODS: Retrospective chart review of all patients presenting to single, tertiary university-affiliated neuro-ophthalmology practice from January 2016 to September 2021 with diagnosis of acute NAION. Patients were determined to have had a presumed previous episode of asymptomatic NAION in the fellow eye if VF defect and corresponding optic nerve head pallor as well as thinning on peripapillary ocular coherence tomography (OCT) and ganglion cell analysis of macular complex were present and alternate causes of VF were excluded. RESULTS: One hundred ninety-two patients with the diagnosis of acute NAION were identified. One hundred thirty-nine had reliable VFs and were included in this study. VF defects in the fellow eye were present in 63 patients (45.4%). Of these, 54 (39%) were determined to represent previous NAION. In 14 of 139 patients (10%), a presumed episode of previous NAION in the fellow eye was asymptomatic. The most prevalent defect in asymptomatic eye was inferior altitudinal defect sparing fixation (7 of 14, 50%). The presence of obstructive sleep apnea, hypertension, diabetes, age, or sex was not predictive of previous episode of asymptomatic NAION. CONCLUSION: Unrecognized presumed previous episode of NAION occurred in a significant proportion of patients with acute NAION (14 of 139, 10.1%). In 100% of cases, the VF defect in the asymptomatic fellow eye was in a hemifield where there was a new loss in the symptomatic eye.