Optic atrophy: A diagnostic sign but not a diagnosis

Optic atrophy is a common final pathway for many retinal and optic nerve pathologies. Unfortunately, the end point of the ophthalmoscopic sign of optic atrophy is uncommonly associated with sufficient diagnostic clues downstream to define an etiology, and the final diagnosis typically rests upon a combination of history, examination, and focused evaluation and testing. When the optic atrophy is associated with other topographically localizing clues (e.g., homonymous hemianopsia, retinochoroidal venous collaterals on the optic disc head or uveitis), the evaluation is simpler. If, however, the patient presents with an isolated optic atrophy, the differential diagnosis is more extensive and complex, and the evaluation can be difficult and expensive. In this review, I will summarize the key historical or examination findings that can lead to either an etiologic diagnosis, or provide guidance to the clinician for a focused laboratory and radiographic evaluation. In unexplained cases, my preferred neuroimaging study is MRI of the head and orbit, with contrast and fat suppression directed along the course of the optic nerve. The main teaching points of this review are to emphasize that 'disc pallor is an ophthalmoscopic finding and not a diagnosis, that 'optic atrophy is not an etiologic diagnosis per se, and that the clinician should use a focused rather than shotgun approach to the evaluation of true optic atrophy.