Assays of OAT activity in lymphocytes and GABA-transaminase activity in platelets were performed, and plasma levels of GABA, ornithine, lysine, glutamic acid and glutamine were measured, and visual fields were examined. A total of 47 subjects, aged 14-78 years, were examined. Twenty-one epileptic patients were off VGB more than 1 year; 11 patients with VGB-induced VFD and 10 with normal visual fields