UVA radiation results in the generation of 8-methoxypsoralen (8-MOP) photoproducts which can be permanently retained in the rat and dogfish lenses and retinas as demonstrated by phosphorescence and EPR spectroscopy, autoradiography and radioactivity of labeled products in these tissues. 8-MOP photoproducts also develop in the corneal epithelium but these cells are replaced within 3–4 days. These experiments suggest that photobound 8-MOP products could accumulate in human lenses and in aphakic or young retinas. Such photoproducts can be prevented by proper UV filtering glasses worn for at least 24 h after ingestion of 8-MOP.

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Exposure to ambient ultraviolet (UV) radiation (longer than 300 nm) over a lifetime appears to play a role in lens aging and nuclear cataract formation. The photochemical generation of fluorescent chromophores has been correlated with the increasing yellow to brown color of the aging lens nucleus and with polypeptide chain cross-linking progressively increasing the insoluble protein level. Acute exposure to 300 nm radiation has also been implicated in human, as well as in animal cortical cataracts. These cortical cataracts develop after rat lenses are exposed to 300 nm UV radiation at irradiance levels of 26 J or more. The Spectra-Shield® lens can be used as a UV filter and will completely prevent the generation of fluorescent compounds within the lens as well as the UV cortical cataracts. The Spectra-Shield lens also prevents the formation of 8-methoxypsoralen (8-MOP) protein photoreac-tion products in UV-exposed rat lenses derived from animals given a single dose of 8-MOP. Furthermore, the Spectra-Shield lens fully retains its ability to reflect all UV radiation after continuous exposure to over 2,500 J of 300 nm UV radiation.

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.

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