Experimental nonpenetrating transscleral cyclodiathermy in rabbits

Acute and long-term effects of contact transscleral cyclodiathermy (CTCD) were studied in rabbits.

In the acute phase, three evenly spaced applications were placed at the limbus in each of four quadrants using the Ophthalmic Diathermy TR4000 (MIRA, Inc., Waltham, MA). Each quadrant of 17 eyes of 13 Dutchbelted rabbits was treated with radio frequencies (RFs) of 1.0 to 4.5, for times of 0.5, 0.75, 1.0 to 3.0, and 4.0 to 10.0 seconds. Eyes were then immediately enucleated and fixed in Karnovsky's solution after the rabbits had been sacrificed with 3 ml of pentobarbital sodium. In the longitudinal phase, four groups of six rabbits each were treated with 20 evenly spaced applications at the limbus at one of four settings: 1.5 RFs/4 seconds, 2.0 RFs/3 seconds, 2.5 RFs/2 seconds, or 3.0 RFs/2 seconds. Intraocular pressures were measured on alternate days for 1 week prior to treatment and for 4 weeks after treatment, following which the eyes were enucleated and fixed in Karnovsky's solution.

Gross examination of the acute phase eyes revealed blanching of the ciliary processes at RF settings of 2.5 and higher with exposure times of 1.5 seconds or longer. Gross and light microscopic studies showed that levels of destruction correlated positively with RF settings and exposure times. Higher RF levels resulted in scleral coagulation necrosis on light microscopy. In addition, there was coagulation necrosis of the pigmented and nonpigmented ciliary epithelium and stroma. Longitudinal phase study showed a significant decrease in intraocular pressure (IOP) in the four groups of rabbits treated over the 4-week follow-up period (P = .005, multivariate analysis of variance [MANOVA]). Rabbits treated at higher RF levels sustained a greater IOP-lowering effect (P = .025, MANOVA). Gross and light microscopic examination revealed focal atrophy, fusion, and fibrosis of the ciliary processes.

Nonpenetrating CTCD results in focal destruction of the ciliary body in rabbits. The authors found that significant reduction in IOP was possible over the 4-week follow-up period in the Dutch-belted rabbits treated, with greater IOP and tissue effects at higher RF settings.