DEVELOPMENT AND RECOVERY OF LASER-INDUCED RETINAL LESION IN RATS MARK BELOKOPYTOV, PHD, MICHAEL BELKIN, MD, GALINA DUBINSKY, PHD, YORAM EPSTEIN, PHD, MORDECHAI ROSNER, MD Purpose: Laser-induced retinal lesions undergo primary and secondary degeneration followed by a partial reduction of the lesion size. To evaluate treatment effects, detailed data regarding the changes of the lesion over time are essential. The purpose of the study is to describe the histologic changes in an argon laser-induced retinal lesion over a period of 60 days. Methods: Argon laser lesions were produced in retinas of pigmented rats. The lesions were examined by light microscopy 1 hour and 1, 2, 3, 20, and 60 days after the exposure. Results: The diameter of the lesion increased 24 hours after photocoagulation and then decreased by day 20. Most pyknotic nuclei seen in the outer nuclear layer 1 hour after lasering disappeared 3 days later. Remodeling began 3 days after lasering. By day 60, partial filling in of the empty area with sliding of adjacent nuclei was observed. Recovery was also seen in the other retinal layers. Conclusion: The course of a laser-induced retinal lesion is gradual: the photoreceptors are damaged first and the damage then spreads to other layers and to the adjacent retina. By day 3, the damage spreading stops, and adjacent cells begin to fill in and remodel the area of the lesion. RETINA X:1–1, 2009 T he retina is the body tissue most sensitive to visible and near infrared laser radiation because the refrac- tive media of the eye concentrates the energy on it. Lasers are widely used in ophthalmology for treatments aimed at restoring vision and postponing blinding pro- cesses. 1– 4 These include treatments for age-related mac- ular degeneration and presumed ocular histoplasmosis syndrome with choroidal neovascularization as well as peripheral laser photocoagulation for proliferative dia- betic retinopathy, focal treatment for cystoid macular edema, demarcation of tears, and subclinical retinal de- tachments. However, accidental retinal exposure to laser beams in medical, research, industrial, or military environments 5–8 frequently causes vision loss. 9 –13 Even retinal photocoagulation treatments of diseases such as diabetic retinopathies and age-related macular degeneration may trigger complications as a result of uncontrolled retinal damage. 14 –19 Extensive research has been carried out on retinal laser bioeffects, development of laser-induced retinal damage, and treatment strategies for the reduction of visual loss caused by laser treatment or accidental exposure. This was studied in humans 16 and in animal models of laser-induced retinal damage in mon- keys, 15,20 rabbits, 21–23 rats, 24 mice, 25 and other spe- cies. 26,27 Because the anatomy of the cholangitic rat retina is closer to the human retinal anatomy than that of the merangiotic rabbit retina, we used the rat model of retinal lesions induced by argon laser to evaluate the efficacy of potential therapies. 24 Few studies fol- lowed photo-induced retinal injuries up to 6 months after photocoagulation 23,28 –30 but with only few early time points, 23 whereas others had only early time points over a few days or weeks. 16,21,22,31–33 As far as we know, no data are available on the natural history of argon laser-induced retinal lesion in the rat model, in which lesion development was examined and mea- sured from 1 hour to 60 days after the exposure. The lesions studied were similar to those used clinically by From the Goldschleger Eye Research Institute, Sackler School of Medicine, Tel Aviv University, Sheba Medical Center, Tel Hashomer, Israel. The authors have no proprietary interest. Reprint requests: Mark Belokopytov, PhD, Goldschleger Eye Research Institute, Sheba Medical Center, 52621 Tel Hashomer, Israel; e-mail: markb120@gmail.com rich3/z7j-retina/z7j-retina/z7j99907/z7j4390-09z xppws S1 9/22/09 6:52 Art: IAE201483 Input-pj 1