Imaging of temperature distribution and retinal tissue changes during photocoagulation by high speed OCT

Considerable improvement in the reproducibility of retinal photocoagulation is expected if degree and extend of the heat-induced tissue damage can be visualized on-line during the treatment. Experimental laser treatments of the retina with enucleated pig eyes were investigated by high speed phase-sensitive OCT. OCT could visualize the increase of tissue scattering during the photocoagulation in a time-resolved way. Immediate and late tissue changes were visualized with more than 15 µm resolution. Changes of the reflectance in the OCT images had a similar sensitivity in detecting tissue changes than macroscopic imaging. By using Doppler OCT slight movements of the tissue in the irradiated spot were detected. At low irradiance the thermal expansion of the tissue is observed. At higher irradiance irreversible tissue changes dominate the tissue expansion. OCT may play an important role in understanding the mechanisms of photocoagulation. This may lead to new treatment strategies. First experiments with rabbits demonstrate the feasibility of in-vivo measurements.