A 28 year‐old man had a 4‐day history of a sore, red right eye. He complained of slight worsening of vision, dislike of bright lights and a gritty sensation: all in his right eye. He denied any previous similar episodes. He was emmetropic (i.e. no refractive error so he didn't need to wear spectacles or contact lenses).

On examination, right visual acuity was 6/12 and left visual acuity was 6/4. His right eye was injected (that is, red and inflamed) particularly around the limbus (ciliary injection). He disliked light being shone into either eye.

Fig. 0003.