8-methoxypsoralen and long ultraviolet effects on the rat lens: experiments with high dosage.

The effect of systemic 8-methoxypsoralen (8-MOP; 100 mg/kg daily) and subsequent long ultraviolet irradiation (UVA; 300 mJ/cm2; peak: 365 nm) on albino and pigmented rat eyes was studied in a 3-dimensional experimental set-up. While 8-MOP and UVA did not cause any ocular pathology when administered alone, a combined application of the two factors caused reversible corneal opacities, and irreversible iris devascularisation and cataracts. The irreversible changes were seen only in the albinos and accompanied by a significant decrease in lens wet weight. Phosphorescence and EPR spectroscopy demonstrated the formation of an 8-MOP-protein photoadduct in the animals treated with both 8-MOP and UVA. The results of this study emphasize the necessity of shielding the eyes of patients on photochemotherapy with protective spectacles.