Light distribution of ocular endophotocoagulator probes and its surgical implications

Ophthalmic endophotocoagulator probe cone angle affects the spot size, working distance, laser output power requirement, tissue exposure time, and uniformity of tissue irradiance, which all affect ease and safety of clinical use. The cone angle and irradiance distribution of several ophthalmic endophotocoagulator delivery systems were studied by directing the laser energy emitted by them on a CCD video sensor at several angles of incidence. The irradiances followed a Gaussian distribution. The measured irradiances were compared to a mathematical model of tissue irradiance that adjusted for the cone angle, probe-tissue distance, and angle of incidence. Using this model, laser irradiances produced by endophotocoagulator probes can be estimated under a wide variety of conditions. At highly oblique angles of incidence, wide-angle probes produce unexpectedly higher and uneven tissue irradiance. When numerous characteristics are considered, probes with a cone angle in the range of 10 degrees have many advantages over narrower or wider angle probes.