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Home > Patient & Family Resources > Health Library > Tonometry
A tonometry test measures the pressure inside your eye, which is called intraocular pressure (IOP). This test is used to check for glaucoma, an eye disease that can cause blindness by damaging the nerve in the back of the eye (optic nerve). Damage to the optic nerve may be caused by a buildup of fluid that does not drain properly out of the eye.
Tonometry measures IOP by recording the resistance of your cornea to pressure (indentation). Eyedrops to numb the surface of your eye are used with most of the following methods.
Tonometry may be done:
Tell your doctor if you or someone in your family has glaucoma or risk factors for glaucoma.
If you wear contact lenses, remove them before the test. Do not put your contacts back in for 2 hours after the test. Bring your eyeglasses to wear after the test until you can wear your contact lenses.
Loosen or remove any tight clothing around your neck. Pressure on the veins in your neck can increase the pressure inside your eyes. Stay relaxed.
Tonometry takes only a few minutes to do.
This type of tonometry is done by an ophthalmologist or an optometrist. Your doctor will use eyedrops to numb the surface of your eyes so that you will not feel the tonometer during the test. A strip of paper containing a dye (fluorescein) will be touched to your eye, or eyedrops containing the dye will be applied. The dye makes it easier for your doctor to see your cornea.
You will rest your chin on a padded support and stare straight into the microscope (slit lamp). Your doctor sits in front of you and shines a bright light into your eye. Your doctor gently touches the tonometer probe to your eye. Your doctor checks the tension dial on the tonometer that measures the IOP of your eye.
Do not rub your eyes for 30 minutes until the numbing medicine has worn off.
Electronic tonometry can be done by a technician, an optometrist, an ophthalmologist, or a family medicine doctor. Your doctor will use eyedrops to numb the surface of your eyes so that you will not feel the tonometer during the test.
You will stare straight ahead, or sometimes look down. Your doctor gently touches the tonometer probe to your eye. Several readings will be taken on each eye. You will hear a clicking sound each time a reading is obtained. After enough accurate readings have been obtained, a beep will sound, and the averaged IOP measurement will appear on the instrument's display panel.
This type of tonometry is done by an ophthalmologist or an optometrist. You do not need drops to numb your eye for this method.
You will rest your chin on a padded support and stare straight into the machine. A brief puff of air is blown at your eye. You will hear the puffing sound and feel a coolness or mild pressure on your eye. The tonometer records the intraocular pressure (IOP) from the change in the light reflected off the cornea as it is indented by the air puff. The test may be done several times for each eye.
Tonometry should not cause any eye pain. Your doctor will use eyedrops to numb the surface of your eyes so that you will not feel the tonometer during the test. You may have a scratchy feeling on your cornea. This usually goes away in 24 hours.
Some people become anxious when the tonometer needs to be touched to the eye. In air-puff tonometry, only a puff of air touches the eye.
There is a very slight risk that your cornea may be scratched during the methods that involve touching a tonometer to your eye. Rubbing your eyes before the numbing eyedrops wear off increases the risk of scratching the cornea. If tonometry causes a scratch on the cornea, your eye may be uncomfortable until the scratch heals, which normally takes about a day.
There is also a very small risk of an eye infection or an allergic reaction to the eyedrops used to numb your eyes.
With the air-puff (noncontact) method, there is no risk of scratches or infection, since nothing but air touches your eyes. But this method is not the best way to measure intraocular pressure.
You should not have any eye pain or vision problems after tonometry. Call your doctor if you feel any eye pain during the test or for 48 hours after the test.
A tonometry test measures the pressure inside your eye, which is called intraocular pressure (IOP). This test is used to check for glaucoma.
Normal eye pressure is different for each person and is usually higher just after you wake up. IOP changes more in people who have glaucoma. Women usually have a higher IOP than men, and IOP normally gets higher as you get older.
10–21 millimeters of mercury (mm Hg)
Higher than 21 mm Hg
Reasons you may not be able to have the test or why the results may not be helpful include:
Chang DF (2011). Ophthalmologic examination. In P Riordan-Eva, ET Cunningham, eds., Vaughan and Asbury's General Ophthalmology, 18th ed., pp. 27–57. New York: McGraw-Hill.
Dielemans I, et al. (1994). The prevalence of primary open-angle glaucoma in a population-based study in the Netherlands: The Rotterdam Study. Ophthalmology, 101(11): 1851–1855. DOI: http://dx.doi.org/10.1016/S0161-6420(94)31090-6. Accessed June 14, 2016.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Current as of: May 5, 2019
Author: Healthwise StaffMedical Review: Adam Husney, MD - Family MedicineE. Gregory Thompson, MD - Internal MedicineChristopher Joseph Rudnisky, MD, MPH, FRCSC - Ophthalmology
Current as of:
May 5, 2019
Medical Review:Adam Husney, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Christopher Joseph Rudnisky, MD, MPH, FRCSC - Ophthalmology
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