Riboflavin and the cornea and implications for cataracts

Riboflavin, also known as vitamin B2, belongs to the class of water-soluble vitamins. The US Food and Nutritional Board established recommended daily allowances (RDAs) of 1.3 mg/day for adult males and 1.1 mg/day for adult females. Riboflavin is not metabolically active, unlike its derivatives flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). The biochemical reactions in which it takes part are numerous, the most important being the biochemical reactions of oxidation-reduction (redox) involving the glutathione reductase. Glutathione (GSH) is a tripeptide with antioxidant properties. Riboflavin ultraviolet A-induced corneal collagen cross-linking is a new therapy to halt keratoconus and secondary corneal ectasia progression. In this contest, riboflavin acts as photosensitizer substance, increasing the production of free radicals that cause cross-linking of corneal stromal collagen. Riboflavin also favors the absorption and concentration of ultraviolet light in the anterior half of the corneal stroma. Severe riboflavin deficiency plays an important role in the etiology of cataract due to its involvement in regeneration of reduced GSH.