Histopathologic observations on human eyes following neodymium: YAG laser cyclophotocoagulation for glaucoma.

PURPOSE: Although Nd:YAG laser cyclophotocoagulation has been extensively used for nearly a decade in treatment of severe glaucoma, there have been remarkably few reports (each of them extremely brief) of histopathological examination of glancomatous human eyes that had been so treated. We undertook this study to provide further details regarding the nature of the lesions produced in this type of ciliary ablation.
METHODS: We chose three representative cases in which a glaucomatous human eye had been subjected to Nd: YAG cyclophotocoagulation, and was subsequently enucleated. To better understand the temporal evolution of the lesions, we selected eyes that were enucleated 1 day, 20 days, and 3 months, respectively, after they had been treated with noncontact Nd: YAG laser cyclophotocoagulation. RESULTS AND
CONCLUSIONS: (1) energy levels ranging from 4.4 Joules to 5.6 Joules were effective in producing appropriate lesions; (2) direction of the laser beam 1 to 1.5 mm behind the limbus caused severe destructive lesions of the pars plicata: (3) toward the periphery of the individual treatment sites, the stroma and ciliary muscle continued to exhibit severe degeneration, as did the epithelium lining the valleys between the crests of the ciliary processes; but in those peripheral zones of individual treatment sites, the epithelium lining the crests of the ciliary processes survived and appears normal; (4) bleb-like separations of the ciliary epithelium from the adjacent stroma, particularly along the posterior aspect of the ciliary body lesions, are a prominent early feature of Nd:YAG cyclophotocoagulation; (5) the pigmented epithelium is more vulnerable to laser energy than is the nonpigmented epithelium of the ciliary body; (6) the destruction of the ciliary epithelium is permanent; (7) deeply pigmented persons have more melanocytes in the ciliary body muscle and stroma than do more lightly pigmented individuals, a circumstance that renders the tissues more vulnerable to laser energy; (8) the ciliary muscle was always severely damaged; (9) no scleral injury was observed other than evanescent, focal areas of edema of the deep sclera; and (10) except in the episclera, inflammatory cells were strikingly few in number, a circumstance providing support for the clinical observation that eyes treated with laser cyclophotocoagulation exhibit less of an inflammatory response than do those treated with cyclocryotherapy.