Potential ocular complications of psoralen-UV-A therapy

During the last decade, psoralens have become increasingly popular in treating psoriasis. The well known photosensitizing action of these drugs has led to concern regarding potential ocular complications, particularly in patients receiving prolonged psoralen therapy. We have demonstrated that this drug can be found in humans and rat lenses and that its presence can lead to a photosensitized enhancement of lenticular fluorescence and phosphorescence. At higher doses, cataracts will develop in experimental animals. We have demonstrated that photoaddition products are generated with certain aromatic amino acid residues in the lens proteins (particularly tryptophan) as well as with the pyrimidine bases of DNA, resulting in the permanent retention of this compound within the ocular lens. Free 8-MOP can also be detected in human lenses for at least 12 h following oral ingestion. When the lens is kept in the dark, the free 8-MOP diffuses out within 12--24 hr. Thus it is possible to prevent photochemical reactions by avoiding exposure to ambient light for 12--24 h following ingestion of the drug. Special glasses, capable of reflecting all UV radiation (up to 400 nm) while completely transmitting the visible radiation (400--750 nm), may also protect the patient.