Tonometry (Intraocular Pressure [IOP] Measurement)

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Between the cornea (the front surface of the eye) and the lens, which is located behind the cornea, there is a clear fluid that helps keep the eye healthy. If there is too much pressure or fluid in the eye, the optic nerve, which is the nerve that carries the images you see from your eye to your brain, can become damaged. This can result in decreased vision. To check the eyes pressure, the tonometry procedure uses instruments called tonometers to measure the intraocular pressure (IOP).

Parts of the Body Involved

  • Eyeball
  • Cornea (the front surface of the eye)
  • Optic nerve (nerve that connects your eye to your brain)

Reasons for Procedure

Tonometry is performed to check the eye pressure. Elevated eye pressure is one of the main risk factors for glaucoma , a group of eye diseases that can cause damage to the optic nerve. If left untreated, glaucoma can cause permanent visual loss or blindness.



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Risk Factors for Complications During the Procedure

A risk factor is something that increases your chance of getting a disease or condition. It is very important that you let your doctor know your medical history prior to any procedure.

The following risk factors might increase the possibilities of complications (such as an incorrect IOP reading): Cornea being thicker or thinner than normal A history of eye surgery, such as LASIK What to ExpectThere are two main types of tonometry: the noncontact (air puff) method and the applanation (flattening of the cornea with pressure) method. The type of tonometry that is performed will depend on the equipment your doctor has and the type of tonometry he or she decides to perform on you. Prior to Procedure For the most accurate pressure readings, your doctor will likely ask you to do the following: Remove your corrective lenses, such as contact lenses AnesthesiaIf using the applanation method, your doctor will place anesthetic drops in your eyes. Then, depending on the type of applanation tonometry performed, your doctor may place a small amount of an orange dye called fluorescein. The dye allows the doctor to check for irregularities on the surface of the eye and then check the intraocular pressure using the Goldmann applanation method.The numbing drops wear off in about 20 minutes and the dye washes out in a few minutes. It is important not to rub your eye while it is numb.
Description of the ProcedureFor both methods you will be asked to sit in an examination chair. To prevent sudden movement or jerking of the head, you may be asked to place your chin in a special cradle and rest your forehead against a bar. The chin cup and forehead rest will balance and steady your head. Noncontact MethodThe noncontact method does not require anesthetic drops because a tonometer instrument does not touch the eye. You will be asked to look into an instrument and a puff of air will be blown into the eye. Applanation Method or the Goldmann TonometryThe applanation method, which is often called the Goldmann tonometry, requires anesthetic drops and fluorescein. When your head is balanced and steady, you will be asked to look into an instrument with a blue light and a probe will flatten the cornea. The pressure required to flatten the cornea determines the eyes pressure. This test does not hurt because the eye is numb. Goldmann tonometry is considered the most accurate method of checking intraocular pressure.Another method of applanation tonometry is the use of a handheld device shaped like a pen. The most commonly used one is called a Tonopen. The doctor will touch this device against your cornea to get pressure readings. Again, it doesnt hurt because the eye is numb.
There are other devices that are used to check eye pressure, but these methods aren't as common. After ProcedureThe doctor will give you your results after the procedure. How Long Will It Take?Getting a tonometry only takes a few seconds. Will It Hurt?This procedure is painless. Some people do experience a slight sting or tingling due to the anesthetic drops. Possible ComplicationsPossible complications or side effects of tonometry are corneal abrasion or an allergic reaction to the anesthetic drops, but this would be extremely rare. Average Hospital StayThis is an outpatient procedure, which is performed in your doctors office and does not require a hospital stay. Postoperative CareTo monitor the pressure and fluids within the eye, your doctor might ask you to schedule a follow-up appointment. OutcomeTwo of the most common uses for the tonometry procedure are glaucoma screening and monitoring. Tonometry for Glaucoma ScreeningIf you are having the procedure for glaucoma screening, your doctor will discuss the results with you and determine treatment options, if needed. Tonometry for Glaucoma MonitoringIf you are having the procedure to monitor an existing diagnosis of glaucoma, your eye care professional will determine if your current medications are appropriately lowering your eye pressure. If your existing treatment plan is not working, your doctor will discuss other treatment options that will work for your specific medical history and pressure readings.
Call Your Doctor If Any of the Following Occurs Contact your doctor immediately if you experience any of the following eye discomforts: BurningExcessive itchingSwellingInflammation (the eye is excessively pink or reddish)Decreased visionAny other eye problem RESOURCES: Glaucoma Research Foundation National Eye Institute CANADIAN RESOURCES: BC Health Guide University of Ottawa Eye Institute References: Brandt JD. Corneal thickness in glaucoma screening, diagnosis, and management. Curr Opin Ophthalmol . 2004;15:85-89. Brandt JD, Beiser JA, Gordon MO, Kass MA; Ocular Hypertension Treatment Study (OHTS) Group. Central corneal thickness and measured IOP response to topical ocular hypotensive medication in the Ocular Hypertension Treatment Study. Am J Ophthalmol . 2004;138:717-722. Duch S, Serra A, Castanera J, et al. Tonometry after laser in situ keratomileusis treatment. J Glaucoma . 2001;10:261-265. Eisenberg DL, Sherman BG, McKeown CA, et al. Tonometry in adults and children. A manometric evaluation of pneumatonometry, applanation, and TonoPen in vitro and in vivo.
Ophthalmology . 1998;105:1173-1181. Kaufmann C, Bachmann LM, Thiel MA. Intraocular pressure measurements using dynamic contour tonometry after laser in situ keratomileusis. Invest Ophthalmol Vis Sci . 2003;44:3790-3794. Komaroff AL, ed. Harvard Medical School Family Health Guide . New York, NY: Simon and Schuster; 1999. Krupin T, Liebmann JM, Greenfield DS, et al. Low-pressure glaucoma study group: the low-pressure glaucoma treatment study (LoGTS): study design and baseline characteristics of enrolled patients. Ophthalmology . 2005;112:376-85. Muir KW, Jin J, Freedman SF. Central corneal thickness and its relationship to intraocular pressure in children. Ophthalmology . 2004;111:2220-2223. Pache M, Wilmsmeyer S, Lautebach S, et al. Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study. Graefes Arch Clin Exp Ophthalmol . 2005;243:763-767. Weigert G, Findl O, Luksch A, et al. Effects of moderate changes in intraocular pressure on ocular hemodynamics in patients with primary open-angle glaucoma and healthy controls. Ophthalmology . 2005;112:1337-1342.
Last reviewed December 2007 by Alexander J. Anetakis, MDPlease be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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