Yield of investigations in patients with questionable nonglaucomatous optic neuropathy

OBJECTIVE: Nonglaucomatous optic neuropathy (NGON) may often be mistaken for normal-tension glaucoma. The distinction between these two entities is important in determining treatment, prognosis, and need for further investigations. We report characteristics of a cohort of patients referred for neuro-ophthalmologic consultation to distinguish between glaucomatous (GON) and NGON. METHODS: Retrospective chart review of patients presenting to a tertiary neuro-ophthalmology practice investigated for GON versus NGON between 2018 and 2020. Patients were classified as GON or NGON based on presence of optic disc pallor, degree of cupping, central visual acuity, and/or when investigations yielded a cause of NGON. RESULTS: Eighty-three patients were enrolled. Seventy-one patients (86%) were deemed to have possible NGON after initial evaluation and having undergone neuroimaging. Of these, 14 patients (19.7%) were determined to have NGON and 7 patients (9.9%) both GON and NGON. The most common causes of NGON were undetermined (8), previous optic neuritis (4), and neurovascular conflict (2). The yield of neuroimaging was low, with abnormalities seen in only 4 of 71 patients (5.6%). No patients with bilateral cupping and no relative afferent pupillary defect (RAPD) had abnormalities on imaging, and no patients with positive imaging required intervention. Patients with NGON had lower intraocular pressure and cup-to-disc ratio and usually had optic disc pallor (86%). Nerve fibre bundle defects were most common in both GON and NGON, with more nasal defects seen in GON. CONCLUSIONS: When NGON resembles GON, the underlying cause is often undetermined, and the yield of neuroimaging is low. The yield of investigating patients with bilateral cupping and no RAPD for NGON is especially low.