Our understanding of glaucoma has undergone dramatic changes in the past decade. The ferment has derived from new epidemiologic information, improved diagnostic methods, and developments in surgical and drug therapy. This review concentrates on primary open-angle glaucoma, the most prevalent form of the disorder in Western countries. Definition Primary open-angle glaucoma usually affects both eyes and combines a particular abnormal appearance of the optic disk (optic-nerve head) with a slowly progressive loss of visual sensitivity (Figure 1). The characteristic appearance of the glaucomatous optic disk is visible by ophthalmoscopy (Figure 2). The present standard for determining visual loss in glaucoma . . .