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Medical Author:

John Sheppard, MD

Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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In this Article

• 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
• Tonometry Index

Who is at risk for glaucoma?

Glaucoma occurs when the normal fluid in the front of the eye chamber, the aqueous humor, is blocked from leaving the eye during the normal aqueous turnover process. This blockage can occur for a number of reasons, the most common of which is simply poor outflow due to chronic open-angle glaucoma. A number of other problems can also impede the ability of the outflow channels to function properly, thus creating elevated IOP. Glaucoma is rarely if ever a disease of excessive aqueous humor production. An eye doctor, your ophthalmologist or optometrist, can usually detect those individuals who are at risk for glaucoma. These patients are called "glaucoma suspects" and must be monitored closely for subtle changes in their visual field or in their optic nerve.

There are many risk factors for glaucoma, including:

• family history of glaucoma
,


• anatomical variations including narrow filtering angles or anatomical damage to the filtering angles
,


• elevated intraocular pressure (IOP),



• diabetes mellitus,



• previous ocular trauma, injury, or surgery,



• use of steroid pills, eye drops, patches, injections, or nasal sprays
,


• excessive pigment in the front or anterior segment of the eye,



• many congenital disorders of the eye such as Peter's anomaly or Sturge-Weber syndrome,



• many degenerative disorders of the eye such as pseudoexfoliation syndrome
,


• extremely advanced cataract
,


• African American heritage,



• proven visual field loss or anatomical changes in the optic nerves
,


• inflammatory disorders of the eye such as iritis, uveitis, or pars planitis,



• many infectious diseases of the eye such as Herpes simplex, toxoplasmosis, Fuch's uveitis syndrome, or shingles (Herpes zoster),



• an extremely thin cornea,
and


• excessively high myopia, generally greater than 6 diopters.

The eye doctor also can diagnose patients who already have glaucoma by observing their nerve for damage or detecting visual field loss with a peripheral visual field test. Patients with glaucoma must be monitored closely for the remainder of their lifetime in order to adequately treat the IOP and assess treatment effectiveness. It is extremely cost effective to avoid visual disability due to glaucoma, enabling the at-risk patient or the patient with glaucoma to have an active lifestyle with functional central and peripheral vision.