Effect of Fiberoptic Diameter in Diode Laser Transscleral Cyclophotocoagulation in Human Autopsy Eyes

Abstract

Contact fiberoptic laser transscleral cyclophotocoagulation (TSCPC) is an aqueous inflow-reducing surgical treatment for glaucoma. One delivery device uses a 600-microm diameter quartz glass fiberoptic with a hemispheric tip. A larger fiberoptic diameter would reduce fluence through conjunctiva and sclera. This study determined the relation of fiberoptic to ciliary body burn diameters after TSCPC with the IRIS Medical SLx diode laser system in human autopsy eyes. Laser energy was applied with two models of delivery probe that were identical except for fiberoptic diameter (600 or 800 microm). Both had hemispheric tips, each with the hemisphere radius equal to the radius of the fiberoptic. Six fresh human autopsy eyes (three pairs) were used, each receiving eight diode laser applications at 1.75 (2 eyes) or 2.0 (4 eyes) watts for 2.5 seconds-four applications per eye with the 600-microm fiberoptic and four with the 800-microm fiberoptic. Eyes were fixed in 10% formalin then opened coronally at the equator. Inner surface burn diameters were measured parallel and perpendicular to the limbus using calipers and an operating microscope at 10x magnification. Ciliary body burns with the 600- and 800-microm fiberoptic tips had nearly the same average diameter, range of diameter, average area, and range of areas. The 800-microm fiber, which has a 78% larger cross-sectional area than a 600-microm fiber, reduces fluence through ocular surface tissue during diode laser TSCPC, theoretically decreasing the risk of surface bums. In this study, the larger fiber gives essentially the same size ciliary body coagulation as obtained with the 600-microm fiberoptic. This suggests that the larger fiberoptic, compared with the standard 600-microm fiberoptic, will be more safe yet equally effective for TSCPC.