Tonometry
Medical Author: John Sheppard, MD
Medical Editor: Melissa Conrad Stöppler, MD
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.
Next: Who is at risk for glaucoma? »
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Last Editorial Review: 1/7/2008
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