What is tonometry?
Tonometry is an eye test that can detect changes in eye pressure long before you are aware of them. The most common type of tonometry test is called a “Goldmann applanation tonometry test.” For times, it has been considered the universal gold standard for calculating IOP. There are other methods of assessing eye pressure, including an alternative type of tonometry called “pneumotonometry,” as well as the use of the Tono-Pen.
Pneumotonometry involves applying air pressure to the eye, using an instrument that resembles an air piston. The instrument blows a brief puff of air into the cornea and measures the pressure in the eye. If it shows abnormal results, your doctor will usually do other tests to confirm your diagnosis. This tonometry is generally considered less accurate than the Goldmann applanation tonometry test.
The Tono-Pen is a handheld device that is shaped like a large marker. Provides digital reading of eye pressure. Your doctor can use it to touch your eye and measure the pressure. Although useful in many cases, the Tono-Pen is considered less accurate than the Goldmann tonometer in people with normal corneas.
Types of tonometry
- Goldmann and Perkins applanation tonometry. The Goldmann Applanation Tonometer measures the force required to flatten an area of the cornea 3.06 mm in diameter.
- Non-contact tonometry
- Ocular response analyzer
- Schiotz tonometer
Tonometry can be performed:
As part of a routine eye exam to check for increased intraocular pressure (IOP), this can increase your risk of glaucoma.
To check glaucoma treatment. Tonometry can be used to find out if the medicine is keeping your IOP above a certain target pressure set by your doctor.
Who needs a tonometry test?
Your ophthalmologist may order the Goldman applanation tonometry test if they suspect you may be at risk for glaucoma. If the air puff test or other eye tests indicate a potential problem, you may be asked to have a tonometry test to confirm or rule out glaucoma.
You may be at higher risk for glaucoma if you are African American or Hispanic. You may also be at higher risk if:
- He is over 60 years’ old
- Have a family history of glaucoma
- Have diabetes
- Have hypothyroidism
- Have other chronic eye conditions or injuries
- Have used corticosteroid medications for long periods
You may also be tested if you have symptoms, such as:
- A gradual loss of peripheral vision
- Tunnel vision
- Severe eye pain
- Blurry vision
- Halos around lights
- Redness of your eye
All of these symptoms can be signs of glaucoma.
When we need this test?
Your eyes are full of different fluids that keep them healthy. New fluid is constantly being produced and old fluid is draining out. But if this drainage system becomes clogged, fluids build up. This increases the pressure inside the eyes.
Sometimes the pressure is due to an eye injury or trauma. Once your eye heals, everything will return to normal. But some people have a drainage system that doesn’t work the way it should.
Over time, the high pressure inside your eye can damage your optic nerve, which sends images from your eyes to your brain. If left untreated, it can cause glaucoma.
Since the disease usually has no symptoms, regular eye exams are a good idea. Your ophthalmologist will monitor your eye pressure using a tonometry test. You can also track pressure changes over time.
Anyone can get glaucoma, but your chances are higher if:
- You are over 40
- You have a family member with glaucoma
- Are African, Hispanic, or Asian
- You have had an eye injury
- You have hyperopia or myopia
- You have been told that your corneas are thin in the middle
- You have diabetes
- You have migraines
- You have circulation problems (blood flow)
Before the tonometry test
Your ophthalmologist will put numbing drops in your eyes so you don’t feel like anything is touching them. Once your eye is numb, your doctor may touch the surface of the eye with a small, thin strip of paper that contains orange dye to tint it. This helps increase the accuracy of the test.
Then your doctor will place a machine called a “slit lamp” in front of you. It will rest your chin and forehead on the supports provided. The lamp will then move towards your eyes until only the tip of the tonometer probe touches your cornea. By slightly flattening the cornea, the instrument can detect pressure in the eye. Your ophthalmologist will adjust the tension until you get an adequate reading.
Because your eyes are numb, you will not feel pain during the procedure. Tonometry is extremely safe. However, there is minimal risk that your cornea will be scratched when the tonometer touches your eye. However, even if this happens, it will usually heal in only a few days.
During a tonometry test
Your doctor can check your eye pressure in two different ways:
- Tonometer. After special numbing drops are put into your eye, your doctor gently holds this pencil-shaped device against the outside of your eyeball. The reading indicates how well the cornea is pushing back.
- “Air puff”. Your doctor may also use an instrument that blows a small puff of air into your eye while looking into a light. This also measures the pressure inside your eyeball.
Both methods are painless and only last a few seconds. If your doctor does the “puff” test, you may feel a small quantity of heaviness against your eye.
The normal result is that your eye pressure is within the normal range. The typical range of eye pressure is 10 to 21 mm Hg.
The thickness of your cornea affects measurements. Normal eyes with thicker corneas have higher readings and normal eyes with thinner corneas have lower readings. A thin cornea with a high reading can be very abnormal (the actual pressure in the eye is higher than what is shown on the tonometer).
Corneal thickness measurement (pachymetry) is required to obtain an accurate pressure measurement.
Talk to your doctor about the meaning of your specific test results.