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A.M. Noury, J. Marshall; Sub–threshold Lens Damage From UVB: A Comparison of Macroscopic, Microscopic and Histological End Points With Analysis of Potential Repair Mechanisms . Invest. Ophthalmol. Vis. Sci. 2005;46(13):836.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: UVB is thought to induce cataract by photochemical mechanisms, implying that every absorbed photon has an effect. However, most existing studies use short–term, macroscopic measures of cataractogenesis which produce thresholds for radiation– induced damage. Our aim was therefore to measure UVB induced lens damage, using different end points, over a range of time intervals and compare the threshold data obtained. This would facilitate the interpretation of existing UVB threshold data and provide further understanding of "sub–threshold" UV injury, repair mechanisms and cataractogenesis. Methods: Two experiments were performed using fresh, dissected, porcine lenses, randomly assigned to a control group or one of three UV exposure groups Exposures were using a 302nm transilluminator source (Jencons) and lasted 20s (0.08J/cm2),160s (0.16J/cm2) and 640s (2.56J/cm2). Lenses were subsequently cultured in clear EMEM (Sigma) for 10 days at 37C. Damage was assessed as follows: Experiment 1 (20 lenses): Lens scatter and anterior surface damage was measured daily using a specifically designed scatter meter and microscope–mounted camera. Experiment 2 (24 lenses): TUNEL stained histological sections were obtained at 2h, 12h, 1 day, 36h, 3 days, 5 days and 7 days post–exposure by fixing one lens from each group, sectioning and staining with colorimetric TUNEL stain (Promega) and haematoxylin. Results: A damage threshold existed in terms of scatter measurements and surface microscopy for exposures between 0.08J/cm2 and 0.16J/cm2 over the ten day period. Dose dependent damage was seen above that threshold which progressed over the incubation period. However, "sub–threshold" changes were observed at 0.08J/cm2 on TUNEL stained sections with increase numbers of apoptotic nuclei compared to controls. Necrotic damage was only observed at the two higher exposures. Conclusions: Radiation damage thresholds in the lens must be interpreted with caution as they depend on the timing and type of damage measured and the repair mechanisms involved. Lens epithelial damage still occurs with "sub–threshold" UVB exposures but may be contained by cellular repair mechanisms, such as controlled apoptosis, to prevent cataractogenesis.
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