Optic neuropathy in ketogenic diet.

A symmetrical, bilateral optic neuropathy is reported in 2 patients being treated with ketogenic diets for seizure control. Laboratory tests suggested a thiamine deficiency, and both patients recovered normal visual function after several weeks of treatment with thiamine. The risk of optic nerve dysfunction occurring during the treatment with a ketogenic diet can be minimised if routine vitamin B supplements are given and periodic evaluation of optic nerve function undertaken.