Glaucoma Progression & Intraocular Pressure

Internal pressure in the eye, or intraocular pressure (IOP), keeps the eyeball from collapsing and is primarily regulated by the inflow and outflow of aqueous humor, the clear liquid that fills the front portion of the eye. Continually manufactured by the ciliary body (a ring of tissue located behind the iris), aqueous humor flows through the pupil into the anterior chamber.

After delivering nutrients to the lens and cornea, the fluid drains from the eye through a spongy network of connective tissue known as the trabecular meshwork. Normally, the steady production and drainage of aqueous humor maintain a stable balance of fluid in the eye and keep IOP within a safe range.

Whether the IOP is at a normal or elevated level, it produces mechanical stress in the wall of the eye (the sclera), keeping the eye inflated. Glaucoma is a process in which one group of nerve cells (the retinal ganglion cells) in the eye die, in part due to injury as they pass out of the eye through the sclera on their way to send visual messages to the brain.

Half of those with glaucoma have normal IOP, so the scleral stress in these eyes is apparently sufficient to destroy ganglion cells. Eyes that have higher-than-normal IOP sometimes tolerate it well, without damage, but in others glaucoma develops.

Open-angle glaucoma damage to ganglion cells leads to a slow, progressive loss of peripheral vision, which in a small number of people causes true visual impairment if not treated. Treatment involves the lowering of IOP to a new target level with medication, laser procedures, or surgery, and several clinical trials show that this is generally effective at substantially reducing progressive damage.

A second form of glaucoma, called angle closure, makes up one third of cases of glaucoma in adults and occurs when aqueous humor doesn't properly pass through the pupil. People with smaller eyes, Asians, and women are most susceptible. In a minority of cases, IOP can rise acutely, causing severe pain, blurred vision, and a red eye. Angle closure, both acute and chronic forms, is initially treated by making a hole in the iris with a laser.

Publication Review By: Susan B. Bressler, M.D., Harry A. Quigley, M.D., Oliver D. Schein, M.D., M.P.H.

Published: 25 Feb 2011

Last Modified: 07 Jan 2015