Background: Sudden visual loss and optic disc edema caused by optic neuritis (ON) is usually followed by significant visual recovery. However, little or no recovery occurs when the loss is caused by atypical ON, especially in patients with neuromyelitis optica (NMO). Optic disc drusen (ODD) is a cause of pseudo optic disc edema and may be a predisposing factor for non-arteritic anterior ischemic optic neuropathy (NAION), thereby mimicking atypical ON. In such cases, if globular concretions are seen protruding from the disc substance, ODD may be suspected. The purpose of this paper is to describe two patients with acute visual loss followed by optic disc atrophy initially labeled as atypical ON. Though not suspected on clinical examination, optical coherence tomography (OCT) revealed deeply buried ODD as a predisposing factor for NAION.
Case presentations: Case 1: A 48-year-old woman had bilateral sequential visual loss associated with optic disc edema. Despite treatment, vision did not improve and severe disc pallor ensued. Atypical ON was suspected. Eventually, she was started on immunosuppressant therapy based on a tentative diagnosis of NMO-spectrum disorder. On examination 5 years later, only severe optic disc pallor was observed, but OCT radial B-scans showed ovoid hyporeflective areas in the retrolaminar region of both eyes, compatible with ODD; this led to a diagnosis of NAION and deeply buried ODD. Case 2. A 35-year-old woman with suspicion of ON in the left eye and a history of previous atypical ON in the right eye was referred for neuro-ophthalmic examination which revealed diffuse optic disc pallor and a dense arcuate visual field defect in the right eye. OCT B-scans passing through the disc showed large ovoid areas of reduced reflectivity in the retrolaminar region of the optic disc in the right eye. These findings helped confirm the diagnosis of NAION in one eye, with deeply buried ODD as predisposing factor.
Conclusions: Deeply buried ODD may be associated with NAION causing irreversible visual loss and optic disc pallor, a condition easily mistaken for atypical ON. Awareness of such occurrence is important to avoid unnecessary testing and minimize the risk of mismanagement.
Keywords: Ischemic optic neuropathy; Neuromyelitis optica; Optic disc drusen; Optic neuritis; Optical coherence tomography.