Intraocular pressure (IOP) is the pressure, or force, inside of your eyes. Specifically, its a measurement of the fluid pressure in your aqueous humor. The eye has a jelly-like substance called vitreous humor filling most of the back part of the eye, and a more-watery liquid called aqueous humor in the front part of the eye, behind the cornea and in front of the iris. Most of the aqueous humor flows out of the eye through the drainage angle, in front of the iris. This equal flow maintains a stable pressure.
An eye care specialist will measure your eye pressure with a test called tonometry. Tonometry measures the pressure inside of your eye by flattening your cornea (the clear part at the front of your eye). The more force that’s needed to flatten your cornea, the higher your eye pressure is. Normal eye pressure is usually considered to be between 10 and 20 millimeters of mercury (mmHg) . Elevated eye pressure with no other symptoms is referred to as ocular hypertension. Chronic elevation of IOP has been implicated in the pathogenesis of primary open-angle glaucoma (POAG) and other vision-damaging problems.
