Potential ocular complications from PUVA therapy and their prevention

During the last decade psoralens have become increasingly popular in treating psoriasis. The well-known photosensitizing action of these drugs has led to increasing concern regarding potential ocular complications, particularly in patients receiving prolonged psoralen therapy. We have demonstrated that this drug can be found in lenses of rats injected (intraperitoneally) with 4-8 mg/kg of 8-methoxypsoralen (8-MOP) and that its presence can lead to a photosensitized enhancement of lenticular fluorescence. Our experiments suggest one mechanism regarding the photosensitizing properties of 8-MOP within the ocular lens. Photo-addition products are generated with certain amino acid residues in the lens proteins which may result in the permanent retention of this compound within the ocular lens. We have recently shown that free 8-MOP can also be detected in human lenses for at least 12 hr following oral ingestion. Since the free 8-MOP tends to diffuse out of the lens during this period of time (as long as photic stimulation is prevented) it may be possible to prevent these photochemical reactions if the patient avoid exposure to ambient light for 12-24 hr immediately following ingestion of the drug. It may also be possible to protect these patients with special glasses which are capable of reflecting all UV radiation (up to 400 nm) while completely transmitting the visible radiation (400-750 nm).