A comparison of neodymium: yttrium aluminum garnet and diode laser transscleral cyclophotocoagulation and cyclocryotherapy

The cyclodestructive effects of cyclocryotherapy and of the neodymium:yttrium aluminum garnet (Nd:YAG) and diode laser transscleral cyclophotocoagulation were investigated in phakic and pseudophakic cadaver eyes using a modified Miyake posterior-view technique and light microscopy. Cyclocryotherapy to -80 degrees C was applied with a 2.5-mm diameter tip, 1 and 2 mm from the limbus. Freezing at the ciliary processes was evident after 10-15 sec and reached a diameter of 3-4 mm by 30 sec. No visible changes were evident grossly in the ciliary processes, crystalline lens, or intraocular lens. Histologically increased separation of cells was observed. Effective noncontact Nd:YAG and diode laser applications to the ciliary processes were observed grossly as tissue blanching and shrinking and pigment dispersion. This effect was obtained by aiming 0.5-1.0 mm behind the limbus at a 1-mm defocus using 4 J of energy for the Nd:YAG and 1.2 J for the diode laser. The diode laser spot size did not affect the tissue response. No damage was observed in the crystalline or intraocular lens with either type of laser. Histologic changes using both lasers were coagulation necrosis with fragmentation and detachment of the ciliary body epithelium. This study suggested that the gross and histologic thermal effects produced by the diode and Nd:YAG laser were similar in the ciliary body. Also, at the time of surgery, these cyclodestructive procedures potentially cause little alteration of the crystalline or intraocular lens.