This topic will help you learn about tonometry and how to prepare for it.
What is a tonometry test?
Tonometry is one of the diagnostic procedures used to measure the internal pressure of the eye. This pressure comes from the clear fluid that nourishes the eye, and it is maintained by balancing the production and drainage of this fluid.
There are several methods for measuring eye pressure, and some do not require any contact with the eye at all. The normal range of intraocular pressure is between 10 and 21 mmHg, and any reading above 21 mmHg is considered high. Measuring eye pressure is also essential for monitoring glaucoma, which is an optic nerve disorder that can be slowed down by lowering the pressure inside the eye.
When is tonometry performed?
Tonometry is performed in several cases, including:
Routine eye examination: It is recommended as part of regular eye exams, especially for people over 40 years old. It helps detect early eye problems such as glaucoma (blue water disease).
Family history of glaucoma: If there is a family history of glaucoma, regular eye pressure testing is advised. Glaucoma can be hereditary, and high eye pressure is one of the main risk factors for developing it.
Presence of certain symptoms: When symptoms such as blurred vision, eye pain, headache, halos around lights, or gradual loss of side vision appear, tonometry should be done immediately, as these may indicate abnormally high eye pressure.
Chronic diseases: Some medical conditions, such as diabetes or high blood pressure, may increase the risk of developing eye problems, including elevated eye pressure. Therefore, tonometry may be performed as part of ongoing medical follow-up.
Use of certain medications: Some medications, such as corticosteroids, can increase eye pressure. If a person takes these medications for a long time, they should have periodic tonometry tests.
Tonometry also helps in the early detection of serious eye conditions such as glaucoma, allowing timely treatment to preserve vision and prevent further health complications.
Types of Tonometry
Applanation Tonometry: Uses a flat-tipped device to gently flatten a small area of the cornea to measure IOP. This is considered the most accurate method.
Continuous Monitoring: Involves using a sensor worn on the eye, such as a contact lens sensor or an implantable device, to continuously track IOP.
Dynamic Contour Tonometry: Utilizes a specialized device with a sensor that touches the eye without altering its shape to record pressure.
Electronic Indentation Tonometry: Uses a handheld device with a small sensor that indents the cornea slightly to measure IOP.
Non-Contact Tonometry (Air-Puff Test): Involves blowing a small puff of air onto the cornea and measuring the eye's reaction. Some devices use a quick puff, while others use a continuous stream of air with visual feedback.
Rebound Tonometry Involves, a small plastic-tipped probe that bounces off the cornea. The device calculates IOP based on the probe’s rebound characteristics without causing pain.Some rebound tonometers devices are designed for home use.
Who is at higher risk and more likely to need tonometry?
People over 40 years old.
Those with a family history of glaucoma or high eye pressure.
People taking steroids for a long period.
Individuals with previous eye injuries or eye surgeries.
How is Tonometry Performed?
The test measures the pressure in the anterior chamber of the eye — the fluid-filled space between the cornea and the iris. This pressure, produced by the aqueous humor, helps maintain the eye’s spherical shape. The unit of measurement used is millimeters of mercury (mmHg).
How to prepare for a tonometry test?
Inform your doctor about your medical history: If you have any chronic conditions such as diabetes, high blood pressure, eye infections, or corneal ulcers, inform your doctor. If you are taking certain medications, mention them as some can affect eye pressure.
Avoid wearing contact lenses: Especially if the test involves the use of eye drops to dilate the pupils. Contact lenses may be affected by the drops, or you may feel discomfort after the test.
Be prepared for eye drops: Sometimes, anesthetic or dilating drops are used. These may cause temporary blurred vision, so be prepared — especially if you need to drive.
Avoid caffeine before the test: Caffeine can temporarily raise eye pressure. To avoid affecting the results, it’s best to skip drinks containing caffeine such as coffee or tea before the test.
Relax during the test: The test is quick and painless, so try to relax and breathe deeply to help reduce tension.
Bring sunglasses: You may experience light sensitivity after the test. Bringing sunglasses can help reduce discomfort and protect your eyes from bright light.
Avoid wearing tight-collared clothing, as it may increase neck pressure and affect IOP readings.
Proper preparation helps ensure the test is done easily and accurately, giving you the best possible results.
Frequently Asked Questions:
Is tonometry safe? Yes, tonometry is generally safe and considered a routine diagnostic procedure. Some individuals may experience minor discomfort, especially when the method involves direct contact with the eye.
How long does tonometry take? The procedure typically takes only a few minutes. It is fast, safe, and non-invasive.
Do some medications increase eye pressure?
Yes, some medications, such as corticosteroids can raise eye pressure. If a person uses them for long periods, they should undergo regular tonometry tests.
