Aqueous humour vitamin B12 and intramuscular cobalamins

Abstract

Intramuscular injection of i mg. cyanocobalamin produced a higher level of total aqueous vitamin B12 as measured by biological assay with Euglena gracilis than I mg. hydroxocobalamin, in patients having cataract extractions I to 3 hours after injections (ten patients in each group) and I5 to 20 hours afterwards (twenty and seventeen patients respectively), in spite of a higher serum level after hydroxocobalamin. In tobacco amblyopia (as in any toxic amblyopia), aqueous humour could form a route of entry to the eye for cyanide (or other toxin) which could then pass towards the retina via the vitreous. Cyanocobalamin is a cyanide-carrier which this work has shown to gain relatively easy entry to the eye, where it may be broken down (e.g. by light) to produce free cyanide ("Trojan horse" hypothesis).