Abstract |
This project was developed with the purpose to estimate the illuminance and the distribution of radiation on intraocular structures after transscleral irradiation with 690nm diode laser, when the intensity and the distribution of it are known at the outer surface of the sclera. The method to accomplish this was: First a computer model was developed that simulates light diffusion due to multiple scattering in sclera stroma. In this model it was employed a Monte Carlo method (random walk algorithm) in Matlab code with its parameters selected with such a way so as to resemble sclera optical properties. Then sclera tissue specimens of known thickness were prepared form fresh cadaver porcine eyes, this specimens were irradiated using a 690nm diode laser delivered through an optical fiber. With an appropriate experimental set up the intensity and the distribution of radiation were measured at the exit plane of sclera. Therefore since the initial and final intensity and its distribution at the surface and exit plane of sclera were known respectively, the adjustment of the model parameters was possible so as to accurately reproduce the measured profiles from various specimen thicknesses. According to our calculations and measurements a sclera specimen of 1 mm thickness transmits approximately two thirds of the incident beam. The diameter of the transmitted part of the beam is approximately double of the scatter free hypothetical propagation profile. The combination of those two factors reduces the available illuminance at the sclera exit plane to one sixth in respect to the hypothetical scatter free beam at the same plane. With the use of this model will be possible the optimization of transscleral applications, for the particular wavelength, for applications as transscleral retinal photocoagulation as well as transscleral photodynamic therapy of the ciliary body, so as to be more efficient with less side effects.
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