Tonometry refers to diagnostic tests that measure your intraocular pressure (IOP), or the pressure inside your eye. There are multiple methods available, and some don’t touch your eye at all. The various test methods can help your eye care specialist detect glaucoma before it causes permanent damage and vision loss.
Tonometry refers to a type of eye test that measures pressure inside your eye (intraocular pressure). It’s one of the essential glaucoma tests. There are a few different methods and ways to do this test, all of which are quick and painless.
Eye care specialists, especially ophthalmologists and optometrists, use tonometry to screen for and diagnose glaucoma. It’s a common part of routine eye exams and more specific exams when you have possible eye injuries or experience certain eye symptoms.
Eye specialists may also use tonometry to monitor your eye pressure if you’re taking certain medications. Monitoring your eye pressure makes sure that those medications don’t cause high intraocular pressure (ocular hypertension) as a side effect.
If you have glaucoma, regular tonometry determines treatment. Tracking your eye pressure is a key way to make sure treatment is effective, so frequent tonometry tests — including with devices you can use at home to take readings on yourself — are common.
Advertisement
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Tonometry measures the pressure of your eye’s anterior chamber. The anterior chamber is a fluid-filled space just behind your cornea at the front of your eye. Pressure from the aqueous humor fluid inside that chamber helps your eyes hold their globe-like shape. The unit of measurement for this is millimeters of mercury (mmHg), the same unit used for blood pressure tests.
Your eye care specialist can use a few different tonometry methods. Those include:
You shouldn’t need to prepare for a tonometry test. One exception is to make sure you don’t wear a tight collar doing the test (either by wearing another shirt or loosening the collar if possible). Pressure around your neck from your clothes can increase your intraocular pressure readings.
What you can expect from tonometry tests can vary depending on the method. If you’re having applanation tonometry, your provider will add eye drops containing an anesthetic and a dye called fluorescein to your eyes. But non-contact tonometry and most other methods don’t need either of these to work.
Some of the most common methods for the tonometry test only take a few seconds. Many of these faster methods work best with calculating an average of multiple readings, so don’t be surprised or think you’ve done something wrong if your eye specialist wants to retake the readings a few times. Other methods (like applanation tonometry) take up to a few minutes. Your eye specialist will tell you more about what to expect during the test.
Your provider can tell you the reading right after they take it.
If you received anesthetic eye drops, don’t let anything touch your eyes until the anesthetic wears off. Anesthetic drops keep you from feeling pain, so it’s easier to injure your eyes while they’re numb.
Tonometry shouldn’t hurt, even if the method used involves touching your eyeball in some way. If you have pain during the test, tell your eye care specialist. You can also ask them more about what to expect regarding that pain, including how long it should last and what you can do about it.
A normal reading for most people is 10 mmHg to 21 mmHg. If your results are outside the normal range, there are a few likely next steps.
If simpler tests show high pressure, your eye specialist will probably recommend using applanation tonometry to verify the readings. If applanation tonometry confirms that your pressure is high, your provider may monitor closely or offer treatment options. They’ll want to schedule regular follow-up visits.
Your eye specialist may recommend that you test your eye pressure at home. Be sure to ask about what to do if you get readings that are outside the normal range. You may need a follow-up visit with your specialist if you get slightly higher-than-normal pressures. But, if you get much higher readings, you may need emergency medical care.
Eye pressure that’s high because of angle-closure glaucoma is a medical emergency that needs immediate treatment. Without quick treatment, angle-closure glaucoma can quickly cause eye damage and permanent vision loss.
Other next steps can vary depending on your specific situation and needs. Your eye specialist can tell you more about what you can expect for your specific case.
Low intraocular pressure is also a cause for concern since it can lead to eye damage and vision loss. Low intraocular pressure is usually anything under 5 mmHg or 6 mmHg. If the pressure in your eye is too low, your eye specialist will talk to you about treatment options and follow-up visits to monitor your eye health.
Advertisement
You might be able to drive right after an eye pressure test. It depends on a few factors. One key factor is if your eye exam involved dilating your eyes (during routine eye exams, dilation happens after the tonometry test). Dilating your eyes will cause light sensitivity, and you may have trouble focusing and reading things up close. These effects usually last for a few or several hours.
Eye specialists also commonly keep disposable shades you can wear after your exam (and these shades can commonly fit on top of eyeglasses if you wear them). These shades can help reduce brightness and glare so you’re more comfortable and can see a little better. And many people feel they can still drive after eye dilation. But if you have any concerns about whether you can drive after an eye exam, you may want to consider having transportation to and from your eye specialist visit.
You might not be looking forward to that puff of air or having a handheld device so close to your eyes, but it’s for a good reason. Glaucoma is a common condition, but the high pressure in your eye that causes it is usually detectable long before you have symptoms or permanent damage.
If you do have high pressure in your eyes, your eye specialist is there to help. Their support might be just what you need to make the pressure inside your eyes easier to manage. And that may also help you feel less stressed about caring for your eye health overall.
Last reviewed on 09/10/2024.
Learn more about the Health Library and our editorial process.
Advertisement
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy