STEPS TO OPTIMIZE TRANSSCLERAL PHOTOCOAGULATION

Background: In transscleral photocoagulation, the desired effect is co agulation of parts of the ciliary body or of the peripheral retina. Ho wever, the application is often limited by the unwanted effect of coag ulation of the sclera. To reduce this effect, the ratio of incident ra diation flux to radiation flux transported through the sclera (and abl e to coagulate the target tissue) should be minimized by the incident beam characteristics. Methods: Monte Carlo simulations for the radiati on transport problem of multiple scattering in the sclera were used to calculate the ratio of transported to incident radiation for differen t parameter settings of beam diameters, optical thicknesses of the scl era and beam angles. To verify the theoretical calculations, an simple optical device utilizing a bulb instead of a laser source was constru cted and applied to enucleated porcine eyes. Results: The theoretical calculations showed that the ratio of incident to transported radiatio n flux can typically be decreased by a factor of three by increasing t he beam radius from 0.35 mm (as used in state-of-the-art laser devices ) to 2 mm. This was confirmed by the experiments. Coagulations of the ciliary body or of the peripheral retina were possible with power dens ities an order of magnitude below the values normally applied with las er sources. Conclusion: To improve transscleral photocoagulation, beam diameters should be increased.