Laser iridectomy

Abstract

The laser energy required to achieve an iridectomy in the human eye is calculated as a function of laser beam radius and pulse duration. Two widely different models of the stromal pigment distribution are used in order to embrace the range of coloured irides encountered in practice. The attendant hazards to the cornea, lens and retina are also considered, resulting both from self absorption and also by thermal conduction from the heated iris. These calculations are used to interpret experimental iridectomies attempted over the last ten years and to provide a theoretical foundation for the specialized techniques of iridectomy currently employed. Finally, a new single pulse technique, suggested by these calculations, is formulated and results of preliminary dye laser experiments presented. These results are very encouraging because full-thickness iridectomies were formed in both blue- and brown-eyed rabbits with only 40 mJ of incident laser energy. It was found that the threshold laser energy required for iridectomy was sensibly constant over the visible spectrum for the brown-eyed rabbit. However, for the blue-eyed rabbit the energy had a pronounced minimum in the yellow portion of the spectrum.