Experimental Evidence For Photochemical Mechanisms In Near Infrared Radiation Induced Cataract

Purpose: to elucidate the photochemical mechanisms in the lens from neat infrared radiation.Methods: Female 6- week- old albino Sprague-Dawley rats were used as the experimental animals . The rat was anesthetized with Ketamine/xylazine,95/14mg/kg bodyweight,20 minutes prior to exposure .Ten minutes before exposure the pupil is dilated on both eyes with tropicamide, 5mg/ml.Then ,the rats were exposed unilaterally in vivo to 1090 nm ,8s exposure time with a 3 mm spot on the anterior lens surface. In first experiment, altogether 15 rats were randomly divided into 5 dose groups of 3 rats with quasi top hat spatial distribution for 0,0.5,0.7,0.9,1.0kJ/cm~2( the output power of 0,4.4,6.2,7.6,8.8W)respectively. At one week after exposure, the difference of light scattering between the lenses from the same animal was measured. Second, based on the first experiment, four post-exposure time groups of 6,18,55,168hrs respectively were exposed unilaterally in vivo to 8s of 1090 nm, 0.6kJ/cm~2 (power5.2 W) quasi-top hat spatial distribution with a 3 mm spot on the anterior lens surface within the dilated pupil. After, the intended post-exposure time, the difference of light scattering between the lenses from the same animal was measured.Results: Exposures of 8s induces light scattering in the lens with a 3 mm spot of at least 0.6kJ/cm~2. Further, after 8s of 0.6kJ/cm~2 within a 3 mm spot on the lens surface, the light scattering increase in the lens was delayed at least 18hrs after the exposure.Conclusion: The current data are consistent with a potential photochemical effect of in vivo exposure of the crystalline lens to near infrared radiation since the onset of cataract after in just above threshold dose was at least 18hrs delayed after the exposure.