Non‐Arteritic Anterior Ischaemic Optic Neuropathy and Its Masquerades: A Comprehensive Diagnostic Review

ABSTRACT Non‐arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in individuals over 50 years and presents with sudden, painless vision loss. However, due to the limited phenotypic repertoire of optic nerve injury, other conditions can closely mimic NAION, leading to diagnostic uncertainty. This review outlines the key clinical, imaging and systemic features that help differentiate NAION from its major masquerades, including arteritic anterior ischaemic optic neuropathy, demyelinating optic neuritis, autoimmune and granulomatous diseases, hereditary optic neuropathies, incipes and vascular abnormalities. Particular attention is given to the diagnostic pitfalls and red flags that should prompt reconsideration of the diagnosis. A hypothesis‐driven approach based on history, examination and targeted investigations is essential to avoid misdiagnosis and inappropriate management. Recognising atypical features early can significantly alter prognosis and guide timely and appropriate therapy.