Modelling of 690 nm Laser Light Transmission Through the Sclera

Abstract

Abstract: : Purpose: To estimate the illuminance on intraocular structures following transscleral irradiation with 690nm diode laser. Methods: A computer model was developed using MATLAB software that simulates light diffusion due to multiple scattering in scleral stroma. We employed a random walk algorithm with parameters resembling scleral microstructure. Scleral tissue specimens of known thickness were prepared form fresh cadaver porcine eyes. The specimens were irradiated using a 690nm diode laser. Forward and backward scattering profiles were obtained by means of digital photography and the model parameters were adjusted so as to accurately reproduce the measured profiles from various specimen thickness. Results: According to our calculations and measurements a scleral specimen of 1 mm thickness transmits approximately two thirds of the incident beam; most of the remaining radiation is backscattered. 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 scleral exit plane to one sixth in respect to the hypothetical scatter free beam at the same plane. Conclusions: This model can be used for the calculation of available 690nm diode laser illuminance for such applications as transscleral retinal photocoagulation as well as transscleral photodynamic therapy of the ciliary body.

Keywords: sclera • laser • ciliary body