Tonometry

Eye Diseases and Conditions Slideshow

Medical Author: John Sheppard, MD
Medical Editor: Melissa Conrad Stöppler, MD

• What is tonometry?
• What is the intraocular pressure?
• Who is at risk for glaucoma?
• How is tonometry done?
• What is tonometry used for?
• Find a local Eye Doctor in your town

What is tonometry?

Tonometry is a method of measuring the pressure in the eye. Tonometry is used to determine the pressure in the eye by measuring the tone or firmness of its surface.

What is the intraocular pressure?

Tonometry is very useful to doctors for detection of the pressure in the eye, or the intraocular pressure (IOP). An elevated IOP can be dangerous because people with varying degrees of IOP elevation may develop damage to the optic nerve. The optic nerve collects all of the visual information from the retina of the eye and transmits that information to the brain, where the signals are interpreted as vision. When changes occur in the optic nerve leading to decreased peripheral vision and loss of the nerve tissues, a diagnosis of glaucoma can be made.

Glaucoma is a fairly common condition, with as many as 10 million sufferers in the United States. Many of these people have not been checked and therefore do not know that they have glaucoma. Thus, glaucoma screening efforts as well as regular eye examinations are essential to detect glaucoma at the earliest possible stages.

Glaucoma is usually, but not always, associated with elevated pressure in the eye Actually, glaucoma is now considered a disease of the optic nerve, or optic neuropathy. Generally speaking, the vision loss in glaucoma usually occurs in both eyes, and is thus termed bilateral. As in many other disease states, the vision loss may not be symmetric, that is, one eye may be worse than the other. Vision loss due to glaucoma often begins with a subtle decrease in peripheral vision. If the glaucoma is not diagnosed and treated, it may progress to loss of central vision and blindness.

Vision loss in the chronic open-angle form of glaucoma generally occurs gradually over many years, while the vision loss of acute angle closure glaucoma may occur within a matter of days if not immediately treated. Since patients with open-angle glaucoma rarely notice their gradual peripheral visual field loss, they may not visit an eye doctor until advanced changes have occurred. Unfortunately, the visual field loss in glaucoma represents permanent damage to the optic nerve and is therefore irreversible. For this reason, glaucoma is often called the sneak thief of sight.