Experimental glaucoma: perimetric field defects and intraocular pressure

Abstract

Purpose: To investigate the relationship between intraocular pressure (IOP) and the progression of visual field defects caused by experimental glaucoma in Macaca mulatta monkeys.

Methods: Perimetric fields were measured by behavioral methods in 18 rhesus monkeys during the course of unilateral glaucoma produced by argon laser treatment of the trabecular meshwork. The monkeys' IOPs were measured by applanation tonometry. Visual field defects were quantified by the mean deviation perimetric index from Humphrey Field Analyzer C24-2, model 630 (Humphrey Allergan, San Leandro, CA, U.S.A.), full-threshold data.

Results: The monkeys' eyes demonstrated considerable variability in their susceptibility to pressure-induced neural damage. For 10 of the monkeys, significant field defects were correlated with the increases in their IOPs and the defects progressed monotonically to end-state glaucoma. For the other monkeys, the mean deviation index was not well correlated with IOP; some eyes withstood pressures in excess of 35 mm Hg for several months before significant reduction in visual sensitivity. However, once they began, the rate of progression of field defects was similar across subjects.

Conclusions: Laser ablation of the trabecular meshwork in monkeys provides a model for investigations of the effects of IOP that are not confounded by other ocular or visual disorders. Behavioral perimetry showed the same intersubject variability in the effects of elevated IOP on visual field sensitivities of monkeys that are common with high-tension glaucoma or ocular hypertension in patients. Thus, these investigations provide additional support for the use of the model for a wide variety of clinical investigations on glaucoma.