Development and recovery of laser-induced retinal lesion in rats

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.