Laser-induced lesion size is controlled in real time based on a two dimensional reflectance image recorded by a CCD array during lesion formation. A feedback system using components of the reflectance image achieves uniform lesions by compensating for light absorption variability in biological media. Lesions are formed in a phantom using an argon laser to simulate retinal photocoagulation. The tissue model consists of an absorptive high temperature black paint layer and an egg white protein layer. Reflectance images are acquired as the lesion forms at a standard frame rate using a 512 × 512 CCD camera attached to an ITI 151 series image processor and a Sun 3/260 computer. A shutter controlled by the computer is closed when certain preset conditions are met in the images. Results show a low variance in the sizes of the lesions (diameter or depth) produced under different irradiation conditions and the ability to produce lesions of a predefined size under varying illumination conditions. Real time control from reflectance images based on certain parameters is demonstrated as a feasible method of controlling lesion size.