Does Inter-Eye Asymmetry of Disc Area Explain Differences in Onset of Nonarteritic Anterior Ischemic Optic Neuropathy?

Background: Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in individuals over the age of 50 years. It is associated with conventional vascular risk factors and structural vulnerabilities including "disc-at-risk." We aim to ascertain if a correlation exists between optic nerve head size and the onset of NAION.

Methods: We performed a retrospective chart review of patients with an ICD-10 diagnosis of unilateral or bilateral NAION who underwent optical coherence tomography (OCT) and visual field testing. The primary outcome measure was the disc area as measured on OCT at a follow-up (minimum 6 months after acute vision loss) of the involved (or first involved for bilateral cases) vs fellow eye. The secondary outcome was the cup-to-disc ratio (CDR) of the first vs fellow eye.

Results: Seventy-three patients were included, of which 58 (79%) had unilateral and 15 (21%) had bilateral NAION, with a median follow-up of 23 months. Between the first eye involved and the fellow eye, there were no statistically significant differences in the mean disc area (1.69 ± 0.29 vs 1.71 ± 0.29, P = 0.7). However, average CDR (0.41 ± 0.20 vs 0.28 ± 0.18, P < 0.001) and vertical CDR (0.42 ± 0.20 vs 0.28 ± 0.19, P < 0.0001) were significantly larger in the involved eye.

Conclusions: Despite no statistically significant differences in the disc area between the affected eye and the fellow eye, CDR was larger in eyes with a history of NAION compared with fellow eyes. Further research is required to elucidate local factors that may increase the risk of NAION in one eye relative to the other.