The appearance of cataract in human lenses mainly consists in the formation of a protein network initiated by oxidative processes. Two types of covalent bondings are produced in the cristallins during cataractogenesis: (1) The formation of C-N bonds produced from amino groups of the cristallin proteins and aldehyd or keto groups derived from the oxidation of sugars or unsaturated fatty acids. (2) The formation of S-S bonds from SH groups specially in the gamma-cristallins. These disulfid bonds are scarcely reducible by reductants such as ascorbic acid or glutathione. Experimentally these SS bonds can be produced in rabbit lenses by incubation with riboflavin in the light. The presence of Pherajod® during the incubation period prevents the oxidation of SH groups.