Definition of Intraocular Pressure

Intraocular Pressure – the pressure within the eye that maintains the eye’s form and structure. Normal intraocular pressure in an adult is 12 to 22 millimeters of mercury (mm Hg). A device called a tonometer measures intraocular pressure, either through light contact against the anesthetized eye or via the force of resistance to a puff of air blown against the eye’s surface (a noncontact method that does not require anesthetic drops).

Elevated intraocular pressure is called ocular hypertension. Lower than normal intraocular pressure is called ocular hypotension.

Intraocular Pressure Causes

Ocular hypertension (greater than 21 mm Hg) is a hallmark sign of glaucoma, an eye condition that, if untreated, results in complete loss of vision. Other health conditions that can increase intraocular pressure include tumors that press against the eye, orbital cellulitis, and graves’s ophthalmopathy.

Increased intraocular pressure damages the cells on the front of the optic nerve (the retinal ganglia), leading to permanent vision impairment. Ophthalmic medications that reduce intraocular pressure work through various mechanisms, depending on the cause of the increased pressure.

Ocular hypotension, in which the intraocular pressure is lower than normal (less than 12 mm Hg), characterizes chronic uveitis (inflammation of the structures of the eye) and of certain tumors of the eye. Ocular hypotension also sometimes accompanies systemic hypotension (low blood pressure) and as a side effect of medications, notably general anesthesia agents.


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