A 36-year-old man with progressive peripheral neuropathies was referred to the eye clinic with failing visual acuity. No cause could be found for his ongoing weight loss, poor appetite, disturbed sleep and worsening painful neuropathies after extensive investigations. Blood tests identified a markedly raised mercury concentration, and further inquiries identified his diet to be rich in fish caught in the Caribbean. Tests carried out on the fish he provided showed a high concentration of mercury in the tissue. Electrophysiology showed changes consistent with published reports on patients regularly exposed to high levels of mercury.

A 36-year-old man was referred to the neuro-ophthalmology clinic with a 3-month history of deteriorating vision, with difficulty in reading. He was also being investigated by the neurology service for peripheral neuropathies. He had an 8-month history of numbness and tingling in both feet and in his fingertips. He had been generally unwell, with poor appetite, weight loss of one and a half stones, diarrhoea, low-energy levels and disturbed sleep. He smoked five cigarettes a day and denied any intravenous drug misuse.

He had no medical history or family history of note. There was no family history of consanguinity.

On examination, his best-corrected vision was 6/18 in the right eye and 6/24 in the left. Anterior segments …