Non-arteritic anterior ischaemic optic neuropathy (NAION) may develop due to severe anaemia and hypotension which is seen in acute blood loss. The devastating visual loss is often irreversible. We report a case of NAION in a 20-year-old healthy woman, who presented on the third day of a heavy menstrual cycle with hypovolaemic shock. On day 2 of admission, she had sudden right eye blurring of vision at the superior field on awakening from sleep. Funduscopy revealed a pale and swollen right optic disc. There was a dense right superior altitudinal visual field defect. Her haemoglobin level was low (3.6 g/dL), but she refused blood transfusion due to her religious belief (Jehovah's Witness) and opted for conservative management. She later developed right optic atrophy with persistent visual field defect despite an improved haemoglobin level of 10.5 g/dL.