Bilateral Sequential Non-arteritic Anterior Ischemic Optic Neuropathy (NAION)

This is a case report of a rare case of bilateral sequential non-arteritic anterior ischemic optic neuropathy (NAION). A 50-year-old Indian gentleman, who is a known case of diabetes and an active smoker, presented with a right eye painless inferior visual field defect upon waking up from sleep. Fundoscopy revealed swollen right optic disc with peripapillary splinter hemorrhage while Humphrey visual field (HVF) showed right inferior altitudinal scotoma. Computed tomography of the brain and orbit proceeded to rule out compressive lesions. Thus, a diagnosis of right eye NAION was made. Three months later, he complained of a worsening visual field of the right eye. His right eye's optic disc was pale; however, the left was hyperemic and swollen with peripapillary splinter hemorrhage. HVF showed right eye tunnel vision while the left eye displayed inferior arcuate scotoma. Further investigation revealed suspicious enhancement of both intra-orbital optic nerves in magnetic resonance imaging suggestive of bilateral optic neuritis. Diagnosis of bilateral atypical optic neuritis was made. Thus, the patient was loaded with intravenous methylprednisolone 1 g/day for five days and subsequently oral steroid in tapering doses along with topical brimonidine tartrate 0.2%. Despite that, his left eye's visual field progressively deteriorated to inferior altitudinal scotoma. Subsequently, the lumbar puncture test performed was unremarkable while repeated MRI of the spine and brain showed no focal enhancing lesion. The patient revealed that he had a history of taking phosphodiesterase type 5 (PDE5) inhibitor (tadalafil) on and off over the past year. Diagnosis of bilateral sequential NAION was made and he was co-managed with the endocrine team to optimize his diabetic status. His subsequent visual field remained static with right eye tunnel vision and left eye inferior altitudinal scotoma. In conclusion, progressive NAION of the same eye or fellow eye is rare and mandates further investigations. It is important to identify and manage all the systemic and local risk factors to prevent further attacks. Although there is no rigid evidence stating that intake of PDE5 inhibitors can directly lead to NAION, patients with co-existing predisposing risk factors should be warned about possible ischemic ocular side effects of PDE5 inhibitors.