LASER ENERGY REACHING THE POSTERIOR POLE DURING TRANSSCLERAL CYCLOPHOTOCOAGULATION

Objective: To measure scattered laser energy reaching the posterior po le during transscleral cyclophotocoagulation. Methods: Transscleral cy clophotocoagulation was performed on 4 cadaver eyes with Nd:YAG noncon tact, Nd:YAG contact, and diode contact lasers. Energy was measured wi th a photodiode through a 7-mm trephined hole in the posterior pole. A verage percentage power, average power, and average energy transmissio n were calculated. American Conference of Governmental Industrial Hygi enists (ACGIH) guidelines were used to calculate allowable energy expo sures for each laser. Results: All 3 lasers transmitted 3% to 5% of th e power to the posterior pole. The average energy transmission was 240 to 260 mJ for all lasers. The contact lasers had an average power tra nsmission of 120 mW. The noncontact Nd:YAG laser, with shorter pulse d uration, had an average pourer transmission of 13 000 mW, significantl y greater than that of the other lasers. The ACGIH guidelines for allo wable energy exposures were 93 mJ for the noncontact Nd:YAG laser, 130 0 mJ for the contact Nd:YAG laser, and 440 mJ for the contact diode la ser. Conclusions: Three percent to 5% of laser power delivered during cyclophotocoagulation reaches the posterior pole. Exposure energies ma y approach or exceed ACGIH guidelines. The clinical significance of th ese findings remains to be shown.