A 35-year old man noticed his vision was abnormal on waking one morning: he had difficulty focusing and making out faces, and could not read a newspaper because the words would disappear. A visit to the opticians revealed a visual field defect on the Humphrey chart (figure 1). An MR brain scan was done on day 15 by the ophthalmologists (figure 2). This showed a lesion with T2 hyperintensity in the region of the right lateral geniculate nucleus of the thalamus, consistent with an infarct. He was otherwise completely well with no other symptoms of note. His only medical history was of squint surgery at 3 years of age. He was an ex-cigarette smoker with no other vascular risk factors. He was on no regular medications and denied illicit drug use. There was no recent neck trauma.