Letter: Cyanocobalamin.
D000550:Amblyopia / Q000188:drug therapy*; D006801:Humans; D006879:Hydroxocobalamin / Q000627:therapeutic use*; D008875:Middle Aged; D012907:Smoking / Q000150:complications; D014805:Vitamin B 12 / Q000627:therapeutic use*
D014805:Vitamin B 12; D006879:Hydroxocobalamin