Simulation and optimization of argon laser iridectomy: influence of irradiation duration on a corneal and lens thermal injury

摘要

A 3-D finite element model of the human eye is developed to study the heat transfers induced by an argon laser absorbed on the iris tissue. The main objective is to explain the appearance of complications inherent to the iridectomy such as corneal burns and lens opacities. Contraction burn preceding the iris opening by photovaporization is studied. The iris temperature threshold fixed as onset for the tissue removal is 300 degrees Celsius. For closed angle glaucoma, the thermal history on the corneal endothelium and lens due to recurrent laser shots with pulse durations of 0.5 sec, 0.05 sec and 0.04 sec are presented and discussed. Typically, an overheating of the lens and cornea endothelium by the side of the iridectomy site is observed. This phenomena is important on the cornea endothelium where the temperature increases to 70 degrees Celsius in case of two recurrent laser pulses of 0.5 sec in duration, 0.43 W in power and 0.5 sec in relaxation time. For irradiation time of 0.05 sec this overheating is much less important and the temperature on the cornea endothelium doesn't exceed 47 degrees Celsius. These computations confirm that short laser pulses decrease the amount of adverse effects and agree well with experiments reported by ophthalmologists.