Experimental glaucoma model in the rat induced by laser trabecular photocoagulation after an intracameral injection of India ink.

A simple and reproducible rodent glaucoma model is required to elucidate the pathophysiology of damage to the optic nerve. We developed chronically elevated intraocular pressure (IOP) unilaterally in rats by injecting india ink into the anterior chamber of one eye using a 30-gauge needle. One week later, trapped carbon particles in the chamber angle formed a black band along the corneal limbus in the injected eyes. We performed direct laser photocoagulation without a gonio lens, and selectively burned the trabecular meshwork. Intraocular pressure was measured every week and laser photocoagulation was repeated until mean IOP in the experimental eyes rose above 25 mmHg. Unilateral IOP elevation was attained in all rats within 4 weeks. Twelve weeks after ink injection, we sacrificed the rats and excised the eyes for histologic analysis. The anterior chamber angle showed peripheral anterior synechia caused by laser photocoagulation, and carbon particles were engulfed by macrophages that infiltrated the ciliary cleft. In the optic nerve head, a remarkable decrease in the nerve fiber layer and cavernous degeneration were observed, suggesting glaucomatous optic nerve damage. This experimental rodent model should facilitate the study of the complex mechanisms involved in glaucoma.