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Laser Energy Reaching the Posterior Pole During Transscleral Cyclophotocoagulation
Jonathan S. Myers, MD;
Mary Gina Trevisani, MD;
Nauman Imami, MD;
Leon W. Herndon, MD;
Myron L. Wolbarsht, PhD;
R. Rand Allingham, MD;
K. David Straub, MD;
M. Bruce Shields, MD
Arch Ophthalmol. 1998;116:488-491.
Objective To measure scattered laser energy reaching the posterior pole during transscleral cyclophotocoagulation.
Methods Transscleral cyclophotocoagulation was performed on 4 cadaver eyes with Nd:YAG noncontact, Nd:YAG contact, and diode contact lasers. Energy was measured with a photodiode through a 7-mm trephined hole in the posterior pole. Average percentage power, average power, and average energy transmission were calculated. American Conference of Governmental Industrial Hygienists (ACGIH) guidelines were used to calculate allowable energy exposures for each laser.
Results All 3 lasers transmitted 3% to 5% of the power to the posterior pole. The average energy transmission was 240 to 260 mJ for all lasers. The contact lasers had an average power transmission of 120 mW. The noncontact Nd:YAG laser, with shorter pulse duration, had an average power transmission of 13000 mW, significantly greater than that of the other lasers. The ACGIH guidelines for allowable energy exposures were 93 mJ for the noncontact Nd:YAG laser, 1300 mJ for the contact Nd:YAG laser, and 440 mJ for the contact diode laser.
Conclusions Three percent to 5% of laser power delivered during cyclophotocoagulation reaches the posterior pole. Exposure energies may approach or exceed ACGIH guidelines. The clinical significance of these findings remains to be shown.
From the Duke University Eye Center (Drs Myers, Trevisani, Imami, Herndon, Wolbarsht, Allingham, and Shields) and Free Electron Laser Laboratory (Dr Straub), Duke University, Durham, NC.
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