EXPERIMENTAL GLAUCOMA - PERIMETRIC FIELD DEFECTS AND INTRAOCULAR-PRESSURE

Purpose: To investigate the relationship between intraocular pressure (IOP) and the progression of visual field defects caused by experiment al 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 trabe cular meshwork. The monkeys' IOPs were measured by applanation tonomet ry. Visual field defects were quantified by the mean deviation perimet ric index from Humphrey Field Analyzer C24-2, model 630 (Humphrey Alle rgan, San Leandro, CA, U.S.A.), full-threshold data. Results: The monk eys' eyes demonstrated considerable variability in their susceptibilit y to pressure-induced neural damage. For 10 of the monkeys, significan t field defects were correlated with the increases in their IOPs and t he defects progressed monotonically to end-state glaucoma. For the oth er monkeys, the mean deviation index was not well correlated with IOP: some eyes withstood pressures in excess of 35 mm Hg for several month s before significant reduction in Visual sensitivity. However, once th ey began, the rate of progression of field defects was similar across subjects. Conclusions: Laser ablation of the trabecular meshwork in mo nkeys provides a model for investigations of the effects of IOP that a re not confounded by other ocular or visual disorders. Behavioral peri metry showed the same intersubject variability in the effects of eleva ted 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.