A method to control irradiation time for laser photocoagulation on the retina.

When performing laser photocoagulation on the retina, the dynamic reflectance of the lesion formed by the laser may be used as a control signal. Using digital filter and estimation techniques on the sampled reflectance signal, the latency time and growth rate of the lesion reflectance are determined. These parameters are then used to estimate the absorption coefficient of the illuminated tissue. From these estimates, the irradiation time of the laser can be accurately determined so that optimum therapeutic effect may be obtained, without overexposing the tissue. The result is consistent lesion formation over any part of the retina.