Whole blood cyanide levels in patients with tobacco amblyopia.

Three patients presented with painless bilateral visual failure due to tobacco amblyopia. The whole blood cyanide levels were raised above those predicted from their high tobacco consumption, approaching lethal levels reported from acute inhalation of cyanide. Each patient had an excessive alcohol intake with biochemical evidence of hepatic dysfunction, the elevated whole blood cyanide levels being attributed to the associated impairment of cyanide detoxification. In each case the improvement in visual acuities following abstinence and hydroxycobalamin therapy was accompanied by a reduction in the whole blood cyanide level to within the normal range. Serial measurements of whole blood cyanide, serum alcohol, and the detection of urinary nicotine provided valuable indices of the patient's subsequent compliance and clinical progress.