Lens opacities after repeated exposure to ultraviolet radiation

Purpose: To investigate the effect of the interval between two, near-thresh old exposures to ultraviolet radiation (UVR) on cataract development. Methods: One eye of Sprague-Dawley rats was exposed twice to 4 kJ/m(2) narr ow band UVR (lambda(MAX)=300 Nn) for 15 min each. The interval between expo sures was 0, 6, 24 or 48 h, One week after the first exposure both lenses w ere removed for photography and measurement of the intensity: of forward li ght scattering to quantify lens opacities. Results: All exposed lenses developed cataract. Forward light scattering wa s the same after double exposure with no interval or a 6 h interval. Forwar d light scattering after a 24 or 48 h interval was nearly twofold greater t han that following no interval or a 6 h interval. The exposed lenses in all groups had mild anterior surface opacities and intense equatorial opacitie s as judged with a stereomicroscope, Conclusion: Two, near-threshold UVR exposures at 0 or a 6 h interval produc e the same degree of lens opacification. When the second exposure follows 2 4 or 48 h after the first, lenticular damage increases. Repair processes be tween 24 and 48 h after exposure appear to be sensitive to UVR, and an addi tional exposure during this time may aggravate cataract development.