Cyanide, smoking, and tobacco amblyopia.

RECENTLY it has been suggested that in so-called tobacco amblyopia, an uncommon condition characterized by centro-caecal scotomata which develops usually in males over 40 years of age, the visual deterioration is due to a failure to detoxicate normally the cyanide present in tobacco-smoke (Wokes and Picard, 1955; Wokes, 1958; Smith, 1961). This may be due to a relative or absolute deficiency of vitamin B12 (Heaton, McCormick, and Freeman, 1958; Smith, 1961).