Psoralen--long-wave ultraviolet therapy and human cataractogenesis.

Cataract formation associated with psoralen--long-wave ultraviolet (P-UVA) therapy has been documented in experimental animals. Presumptive P-UVA cataracts in humans have also been reported recently. Cataracts from two patients on P-UVA therapy were subjected to high-resolution phosphorescence spectroscopy. The lens homogenates from these two patients showed phosphorescence peaks identical (in shape and lifetime) with the previously reported 8-methoxypsoralen lens protein photoproduct seen in P-UVA-treated cataractous rat lenses. The data provide objective proof that these phototherapeutic drugs can generate specific P-UVA photoproducts in human lenses. Similar photoproducts have previously been demonstrated in experimental (rat) P-UVA cataracts.

Nuclear magnetic resonance analyses of the cold cataract: whole lens studies.

Pulse nuclear magnetic resonance (NMR) magnetization decay studies were performed on normal and cold cataractous rat lenses. Computer analyses of the decay curves have been interpreted to reflect two types of water within the lens that do not exchange rapidly. Upon lowering the temperature in the presence and absence of 5% acrylamide (a known agent that prevents the cold cataract phenomenon), significant differences in the relaxation rates of one water fraction were noted. 2H (NMR) spectra on young rabbit and human lenses showed temperature-related linewidth changes, which are significantly diminished in lenses incubated in acrylamide. 31P spectra also showed similar inorganic phosphate linewidth changes and also reflected progressive alterations in the metabolic state of these lenses. These studies demonstrate the potential of NMR methods for monitoring physicochemical parameters in the normal and cataractous mammalian lens.

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.