The change in light reflection of the retina during therapeutic laser photocoagulation

The increase in light reflection, which is associated with a therapeutic coagulation of the retina, was examined as a measure for the degree of the tissue damage. Retinal coagulations were generated in chinchilla rabbits using an argon laser and a slitlamp microscope with a contact lens. A helium-cadmium laser was directed coaxially to the argon laser into the eye, and helium-cadmium wavelength light reflected from the coagulated area was measured with a microphotometer attached to the slitlamp microscope [3]. The reflection change was correlated to the lesion size and also with the theoretical extent of retinal damage which was calculated using a model for the light-induced thermal denaturing of proteins [1]. The transient increase in the average reflection from the coagulated area had approximately the same time course as the volume of the damaged tissue. By analysis of the increase in reflection and the expansion of tissue damage it was possible to predict the development of the lesion from the beginning phase of the reaction [12]. The results indicate that measurements of the transient increase in the average reflection might provide information for the feedback control of laser treatment in patients [14].