Histologic observations of the lenses of psoralen + UVA treated albino rats and a theory as to the underlying mechanism.

Histologic studies of the lenses of 8-methoxy-psoralen and UVA treated rats revealed that morphologic damage appears first in the epithelium weeks before the onset of any slitlamp observable opacities. The bow region of the lens subsequently shows abnormal morphology, including rounded rather than elongating cells and a dramatic reduction in the number of nucleated fibres. With time, more and more of the cortex becomes involved, in the worst cases progressing to total liquifaction of the outermost cortex. The deeper cortex maintains an ordered pattern. Protected by the upper lid from UVA radiation, the upper lens is never as severely involved as the inferior lens. These findings are consistent with the hypothesis that the basis of the psoralen cataract is genetic damage to lens epithelial cells with subsequent formation of anomalous cortical fibres.