Development of laser-induced retinal damage in the rabbit

Background: Laser lesions may induce retinal damage that is larger than expected from the size of the coagulated area. This study was designed to follow the development of laser-induced reduction in retinal function and to correlate it with structural changes. Methods: Pigmented rabbits were treated in one eye with 225 argon laser lesions. The ERG responses were recorded at different times after treatment. The effect of the laser treatment upon the functional integrity of the retina was assessed from the ERG responses. Structural damage was examined by light microscopy. Results: Shortly (1-2 h) after laser treatment, the ERG responses were reduced by about 50%. ERG deficit continued to develop and reached a maximal level about 24 h after treatment. Thereafter, slow recovery was observed but permanent deficit, relative to the initial laser effect, was seen even 30 days after treatment. Histological observations indicated extensive serous retinal detachment between laser lesions that developed within 24 h after treatment. At 30 days post-treatment, lesioned areas were completely destroyed and heavily pigmented. The retina between lesions was attached to the pigment epithelium but exhibited different degrees of structural damage. Conclusions: The immediate laser damage is confined to the coagulated areas while secondary functional damage develops within 24 h and probably reflects serous retinal detachment between lesions. The serous retinal detachment completely resolves with time but may induce permanent structural abnormalities in non-coagulated retinal areas that is reflected in a functional deficit larger than the initial laser effect.