Recovery of the electroretinogram in rabbits after argon laser photocoagulation

Argon laser is widely used to coagulate the diabetic retina in order to inhibit the proliferative stage of diabetic retinopathy. Ten pigmented rabbits underwent retinal photocoagulation with argon laser. Retinal function was assessed electroretinographically before treatment and at different time intervals after treatment. The ERG responses measured 4-7 days after treatment were reduced in amplitude by a degree which was proportional to the number of laser applications. In five eyes that were treated with at least 1000 applications the ERG responses were very small when measured 4 days post-treatment. However, a gradual recovery was observed and within 2 months the ERG responses approached the normal pretreatment amplitudes. Histological findings from light and electron-microscopy suggested that the ERG recovery could not be solely explained by healing of the coagulated areas. Structural differences were seen in the pigment epithelial layer between a retina obtained immediately after treatment and one studied after ERG recovery. It is suggested that changes in the electrical resistance of the pigment epithelium may contribute to the ERG reduction seen immediately after laser treatment in the rabbit and to the increase in the ERG amplitude observed during the apparent functional recovery of the retina.