Normal intraocular pressure ranges from 10 to 21 millimeters of mercury, according to eMedicineHealth. Patients with glaucoma tend to have intraocular pressure greater than 21 millimeters of mercury. In general, higher pressure presents a greater risk to the optic nerve, explains the Glaucoma Research Foundation.
Increased eye pressure indicates a person is at risk for glaucoma, but glaucoma is only diagnosed when optic nerve damage occurs, states the National Eye Institute. Some people tolerate high eye pressure better than others, and not all patients with increased eye pressure develop open-angle glaucoma. People at increased risk for glaucoma include all adults over the age of 60, African-Americans over the age of 40 and individuals with a family history of glaucoma.