A previously fit 37-year-old woman gave a 5-day history of painless decreased vision in her right eye, perceived as a grey patch over the front of the vision. This had remained unchanged since she had first noticed it. On examination, her right eye visual acuity was 6/36 and she could see 2/11 of the Ishihara plates. There was a right relative afferent pupillary defect. Dilated fundal examination revealed right optic disc swelling and retinal thickening extending to the macula (figure 1A). Optical coherence tomography confirmed the optic disc swelling and retinal thickening but also showed subretinal fluid in the macula (figure 1B).