Histopathology of continuous wave neodymium: yttrium aluminum garnet and diode laser contact transscleral lesions in rabbit ciliary body. A comparative study.

Neodymium: yttrium aluminum garnet (Nd:YAG) laser transscleral cyclophotocoagulation has been shown to be an effective method of lowering intraocular pressure (IOP). Transmission and absorption features of diode laser radiation (810 nm) make these new laser sources suitable for production of transscleral thermal lesions. The transscleral effects on rabbit ciliary body of Nd:YAG and diode laser wavelengths were compared using a CW Nd:YAG laser and a CW Aluminum Gallium Arsenide diode laser. Both lasers were delivered by silica optic fibers, 600 microns in diameter. Eight rabbits were treated by applying the optic fiber 0.5 mm from limbus while increasing energy values from 0.2-2 J. The lesions produced at equal energy values underwent gross and histologic and ultrastructural comparison. Gross examination revealed threshold lesions at 1 J energy for the Nd:YAG laser and 0.8 J for the diode laser. The diode laser produced transscleral thermal lesions of the rabbit ciliary body comparable to those achieved by the Nd:YAG laser. The histologic and ultrastructural study showed that diode laser radiation produced more remarkable damage to the ciliary pigmented structures, causing deep coagulation necrosis of the pigmented epithelium, wide disorganization of the collagen in the stroma, and intravascular coagulation phenomena in the ciliary vessels. Before the introduction of these new laser sources in clinical transscleral procedures, further investigation is needed to determine optimal energy levels.