Therapeutic range in transscleral contact cyclophotocoagulation.

Laser contact cyclophotocoagulation (CP) increasingly replaces noncontact CP and cryotherapy as it produces less damage to the conjunctiva and sclera. However, the optimal wavelength and protocol for treatment have not yet been firmly established. We used a contact continuous-wave (cw)-Nd:YAG laser at 1064 nm (Meridian-Microruptor III) with a bare fiber. A total of 30 freshly enucleated porcine eyes with brown irides were treated within 12 h of enucleation. The intraocular pressure was kept at 35-40 mmHg with an infusion system. The fiber was placed at a 1.5-mm distance from the limbus perpendicularly to the scleral surface, and applications were made using power levels ranging from 1.0 to 10.0 W for exposure periods of 0.5, 0.7, 1.0, 1.5, 2.0, 3.0, and 4.0 s. A just-visible whitening of the ciliary body was defined as a minimal effect, a complete whitening without loss of ciliary structures was defined as a medium effect, and a complete whitening with loss of ciliary structures was defined as a maximal effect. Supramaximal "pop" effects could be identified by the typical sound and the destruction of the ciliary body. Pop effects originate from a sudden overheating, which leads to the formation of small gas bubbles. Using an exposure duration of 0.5 s, no pop effect or maximal effect was observed. For longer exposure periods the therapeutic range decreased continuously (3.7 +/- 2.7 W for 0.5 s, 0.3 +/- 0.3 W for 4.0 s).(ABSTRACT TRUNCATED AT 250 WORDS)