Risk Factors for Fellow Eye Involvement in Nonarteritic Anterior Ischemic Optic Neuropathy

Background: Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in individuals older than 50 years. Demographic, ocular, and systemic risk factors for NAION have been identified, and we sought to determine which, if any, of these factors also increase risk of NAION in the fellow eye. Methods: We performed a retrospective chart review of patients with "ischemic optic neuropathy" (based on International Classification of Disease [ICD] codes) seen at a single eye center between 2007 and 2017. Patients who met diagnostic criteria for unilateral NAION without fellow eye optic neuropathy at diagnosis were included. Demographic information, ocular comorbidities, and systemic diagnoses were recorded, in addition to whether the fellow eye developed NAION during the follow-up period. Univariate and multivariate Cox proportional hazard regression were used to calculate hazard ratios (HRs) for fellow eye involvement. Results: Three hundred eighteen patients were identified by ICD codes, and 119 were included in the study. Twenty-nine (24%) patients developed NAION in the fellow eye over the mean follow-up period of 3.6 years (range: 1 month-11 years). Significant risk factors for fellow eye NAION included the presence of bilateral optic disc drusen (ODD, HR 2.78, 95% confidence interval [CI] 1.12-6.90, P = 0.02) and noncompliance with continuous positive airway pressure (CPAP) in patients with moderate-to-severe obstructive sleep apnea (HR 4.50, 95% CI 1.79-11.3, P = 0.0015). Conclusions: Bilateral ODD and noncompliance with CPAP when indicated are associated with increased risk of NAION in the fellow eye. Patients with these risk factors should be counseled on the potentially devastating visual consequences of bilateral NAION, and compliance with CPAP should be stressed when appropriate