Tonometry: objectives, procedures and results

Definition

What is tonometry?

Tonometry is an eye test that measures the pressure inside your eyeball, or what is known as the intraocular pressure (IOP). The tool used in tonometric checks is called a tonometer.

Generally, this test is used to check for glaucoma, an eye disease that can cause blindness due to damage to the nerve at the back of the eye (optic nerve).

Normally, the eye fluid drains out through the drainage angle of the eye. In most cases of glaucoma, damage to the optic nerve occurs due to a build-up of fluid that can't drain out of the eye properly. The buildup is what then increases the pressure on the eyeball.

Tonometry tests can be done every few months or years as part of a routine eye exam. In addition, because intraocular pressure can change over time, tonometry is not the only test used to check for glaucoma.

If the IOP is high, additional eye examinations such as ophthalmoscopy (funduscopy), gonioscopy, and visual field tests may be required.

What are the different types of tonometry?

Here are the 3 most common types of tonometric checks:

1. Goldmann's tonometry

Tonometry examination applanation Goldmann's is the most common type of test performed as the standard for examining intraocular pressure, with the most accurate results.

This test flattens part of your cornea to measure eye pressure and uses a microscope slit light to look at your eye with a tonometer.

2. Electronic tonometry

This test also has high accuracy, although sometimes the results differ from Goldmann's tonometry. In this test, the doctor will place a soft instrument with a rounded tip that looks like a pen directly against the cornea of ​​the eye. The intraocular pressure reading is shown on a small computer panel.

3.Non-contact tonometry (pneumotonometry)

This type of tonometry doesn't touch your eye, but uses a puff of air to flatten the cornea. This type of tonometry is not the best way to measure intraocular pressure, but it is often used as a simple and easy way to check intraocular pressure, especially in children.

When should I have tonometry?

In general, doctors will recommend undergoing a tonometry examination if you are suspected of having glaucoma symptoms, such as:

• decreased vision, especially at the edge of the eye
• tunnel vision (eyes like looking from a tunnel)
• severe eye pain
• blurred vision
• see a rainbow circle around a lamp or light
• red eyes

In addition, you are also advised to do this examination if you are among people who have risk factors for glaucoma.

According to the American Academy of Ophthalmology, here are the risk factors for glaucoma:

• are over 40 years old
• have a family member with glaucoma
• Asian, African, or Hispanic descent
• have abnormal eyeball pressure
• suffers from nearsightedness or farsightedness
• have experienced trauma or injury to the eye
• taking long-term steroid medication
• has a thin cornea in the center of the eye
• have a thinning optic nerve
• suffer from diabetes, migraines, high blood pressure, or other illness

Process

What should I do before undergoing tonometry?

You don't need to make special preparations before undergoing the examination. However, there are a number of things that need to be considered, such as:

• If you wear contact lenses, remove them before the test.
• Tell your doctor if you have a history of eye diseases, such as corneal ulcers or eye infections.
• Also tell your doctor if there is a history of glaucoma in your family.
• Always tell the medical team and doctor about the medicines you are taking.

How is the tonometry process?

The tonometric check process only takes a few minutes. Here are the steps:

1. You will be given eye drops to anesthetize your eyes, so you won't feel the tonometer sticking during the test.
2. A strip of paper containing the dye will touch your eye or you will be given eye drops containing the dye. The dye aims to make it easier for your doctor to see your cornea.
3. Place your chin on the support and look directly at the microscope (slit lamp) as directed by the doctor.
4. In the Goldmann method, doctors will use probe a tonometer that is gently placed in the eye, to measure the intraocular pressure in your eye.
5. The same applies to electronic methods. The difference is, the IOP measurement results will be displayed on the monitor panel or screen.

In the non-contact or pneumotonometric method, the process is slightly different. With this method, you will not need a drip anesthetic. The steps for pneumotonometry are:

• Place your chin on the support and look straight into the machine as directed by the doctor.
• A puff of air will be blowing in your eye in no time. You will hear a puff and feel a cool sensation or light pressure in the eye.
• The tonometer records the IOP of changes in light reflected from the cornea. The test can be done several times for each eye.

What should I do after undergoing this examination?

You may feel itchy cornea after undergoing tonometry. However, this usually goes away within 24 hours. Some people may become anxious when the tonometer touches the eye. In the pneumotonometry method, only a puff of air touches the eye.

Call your doctor if you have eye pain during the test or for 48 hours after the test.

Explanation of the test results

What do my test results mean?

Normal eye or intraocular pressure may vary from person to person, and is usually higher after you wake up. However, according to the Glaucoma Research Foundation, the normal size of the eyeball (intraocular) pressure is generally between 10-20 millimeters of mercury (mmHg). Eye pressure that is too low or too high has the potential to damage your vision.

Increased intraocular pressure doesn't necessarily mean you have glaucoma. People who have IOP results higher than 20 mmHg but don't have optic nerve damage may have a condition called ocular hypertension. Even so, this ocular hypertension can develop into glaucoma at any time.

Glaucoma occurs when high intraocular pressure has damaged the optic nerve in the eye. This nerve damage results in decreased quality of vision. If the patient is not treated immediately with the right glaucoma treatment, this condition has the potential to lead to total blindness.

Side effects

What are the possible side effects after undergoing tonometry?

Generally, tonometry is a safe and minimal risk examination. However, if you undergo an examination using the Goldmann method, there may be blisters on your cornea (corneal abrasion). These blisters usually go away on their own within a few days.

However, if you feel any discomfort in your eye that doesn't go away after undergoing the examination, let your doctor know immediately.