Tonometry is an eye test that measures intraocular pressure, or the pressure inside the eye. It is commonly used to help detect ocular hypertension and glaucoma, conditions that can damage the optic nerve and lead to vision loss if untreated. Several types of tonometry are available, including Goldmann applanation, air-puff, rebound, and handheld methods.
As people age, regular eye exams become increasingly important. Vision changes are not always solved with reading glasses or a stronger prescription. Some eye conditions develop silently and may not cause obvious symptoms until permanent damage has already occurred.
One of the most important tests used during comprehensive eye exams is tonometry, which measures intraocular pressure.
Eye pressure plays a major role in diagnosing and monitoring glaucoma, one of the leading causes of irreversible vision loss. In Arizona, where many communities include older adults and retirees, routine eye pressure testing is an important part of long-term vision care.
What Is Tonometry?
Tonometry is a diagnostic test that measures intraocular pressure (IOP), or the fluid pressure inside the eye.
The eye continuously produces a clear fluid called aqueous humor. This fluid circulates through the front part of the eye and drains through a specialized drainage system. When fluid does not drain properly, pressure inside the eye can rise.
Elevated eye pressure does not always cause symptoms, but over time, it may damage the optic nerve.
The optic nerve carries visual signals from the eye to the brain. Damage to this nerve can lead to permanent vision loss.
What Is Normal Eye Pressure?
Normal eye pressure is commonly considered to be between 10 and 21 mmHg, though ranges may vary slightly depending on the source and individual patient factors.
A reading above the normal range does not automatically mean a person has glaucoma. Some people have higher-than-average pressure without optic nerve damage, a condition known as ocular hypertension.
Others may develop glaucoma even with eye pressure in the normal range, known as normal-tension glaucoma.
This is why tonometry is only one part of a comprehensive glaucoma evaluation.
Why Is Measuring Eye Pressure Important?
Tonometry helps eye doctors assess whether a patient may be at risk for glaucoma or other pressure-related eye conditions.
Elevated eye pressure can contribute to optic nerve damage, especially when left untreated.
Tonometry may help detect:
- Ocular hypertension
- Open-angle glaucoma
- Angle-closure glaucoma
- Risk of optic nerve damage
- Response to glaucoma treatment
Because glaucoma often develops without pain or early vision changes, eye pressure testing is essential for early detection.
Who Needs a Tonometry Test?
Tonometry is commonly performed during routine eye exams, especially for adults over age 40.
You may need eye pressure testing if you have:
- A family history of glaucoma
- Diabetes
- High blood pressure
- Previous eye injury
- History of eye surgery
- Severe nearsightedness
- Long-term steroid use
- Gradual loss of peripheral vision
- Blurred or tunnel vision
- Eye redness or pain
- Halos around lights
People of certain ethnic backgrounds may also have a higher risk of glaucoma and may need earlier or more frequent screening.
Symptoms That May Suggest High Eye Pressure
Most cases of elevated eye pressure do not cause symptoms.
However, acute angle-closure glaucoma can cause sudden and severe symptoms, including:
- Intense eye pain
- Redness
- Headache
- Nausea or vomiting
- Blurred vision
- Halos around lights
This is a medical emergency and requires immediate attention.
Types of Tonometry
There are several methods used to measure intraocular pressure. Each has advantages depending on the patient, setting, and clinical need.
Goldmann Applanation Tonometry
Goldmann applanation tonometry is often considered the reference standard for measuring eye pressure.
During this test, numbing drops are placed in the eye. A small amount of fluorescein dye may also be used. The patient sits at a slit lamp with the forehead and chin positioned securely.
A small probe gently touches the surface of the cornea to determine how much force is needed to flatten a small area.
Although the idea of something touching the eye may sound uncomfortable, the numbing drops make the test painless for most patients.
Goldmann tonometry is widely used because of its accuracy and reliability.
Perkins Tonometry
Perkins tonometry is similar to Goldmann tonometry but uses a handheld device.
This makes it useful for patients who cannot sit comfortably at a slit lamp, including individuals with limited mobility.
Like Goldmann testing, Perkins tonometry requires numbing drops and direct contact with the cornea.
Pneumotonometry
Pneumotonometry uses a small probe that rests gently against the cornea while air pressure helps determine intraocular pressure.
This method can be useful in certain clinical settings and may provide reliable measurements in specific patients.
It also requires contact with the eye, so numbing drops are typically used.
Air-Puff Tonometry
Air-puff tonometry, also known as non-contact tonometry, measures eye pressure without touching the eye.
Instead, the device releases a quick puff of air toward the cornea. The instrument measures how the cornea responds to the air pressure.
Because nothing physically touches the eye, numbing drops are not usually needed.
Many patients are familiar with this test because it is commonly used during routine vision screenings. However, it may be slightly less precise than Goldmann applanation tonometry, especially in patients who require careful glaucoma monitoring.
Rebound Tonometry
Rebound tonometry uses a small, lightweight probe that briefly contacts the cornea and rebounds back to the device.
It is quick, portable, and often well tolerated.
This method is commonly used for:
- Children
- Patients who have difficulty sitting still
- Screening environments
- Home or bedside measurements in select cases
Rebound tonometry may not always require numbing drops, depending on the device and patient.
Is Tonometry Painful?
Tonometry is generally not painful.
With contact methods, numbing drops are used to prevent discomfort. Patients may feel mild pressure or awareness during the test, but it usually lasts only a few seconds.
Air-puff tonometry may feel surprising but does not hurt.
Can Corneal Thickness Affect Eye Pressure Readings?
Yes. Corneal thickness can influence tonometry results.
A thicker cornea may produce an artificially higher reading, while a thinner cornea may produce a lower reading than the true internal pressure.
For this reason, eye doctors may also perform pachymetry, a test that measures corneal thickness, especially when evaluating glaucoma risk.
Is High Eye Pressure the Same as Glaucoma?
No.
High eye pressure increases the risk of glaucoma, but it does not always mean glaucoma is present.
Glaucoma diagnosis usually involves several tests, including:
- Tonometry
- Optic nerve examination
- Visual field testing
- Optical coherence tomography (OCT)
- Corneal thickness measurement
- Gonioscopy to examine the drainage angle
A complete evaluation helps determine whether pressure is causing optic nerve damage.
Why Eye Pressure Testing Matters in Arizona
Arizona has a large aging population, and glaucoma risk increases with age. Many patients may not notice early signs because glaucoma often affects peripheral vision first.
By the time central vision is affected, damage may already be advanced.
Routine eye exams that include tonometry can help detect pressure-related concerns before vision loss becomes noticeable.
Arizona’s bright sunlight and dry climate may also contribute to general eye discomfort, making it even more important to distinguish surface irritation from deeper eye conditions that require medical evaluation.
The Bottom Line
Tonometry is a quick, important test that measures eye pressure. It plays a key role in detecting ocular hypertension and glaucoma, both of which can threaten vision if left untreated.
While eye pressure alone does not diagnose glaucoma, it provides valuable information when combined with optic nerve imaging, visual field testing, and a comprehensive eye exam.
Regular eye pressure checks are especially important for adults over 40, individuals with diabetes or high blood pressure, and anyone with a family history of glaucoma.
Frequently Asked Questions
What does tonometry measure?
Tonometry measures intraocular pressure, which is the pressure inside the eye.
What is normal eye pressure?
Normal eye pressure is commonly considered to be around 10 to 21 mmHg, though individual factors can affect interpretation.
Does high eye pressure always mean glaucoma?
No. Some people have elevated eye pressure without optic nerve damage. However, high pressure increases glaucoma risk and should be monitored.
Is tonometry painful?
No. Most tonometry tests are painless. Contact methods use numbing drops, while air-puff tonometry does not touch the eye.
How often should eye pressure be checked?
Most adults should have eye pressure checked during routine comprehensive eye exams. People over 40 or those with glaucoma risk factors may need more frequent testing.
Which tonometry test is most accurate?
Goldmann applanation tonometry is widely considered the reference standard for measuring eye pressure.
Can glaucoma occur with normal eye pressure?
Yes. Normal-tension glaucoma can occur even when measured eye pressure falls within the normal range.
Conclusion
Eye conditions such as glaucoma can have long-term effects on your eyesight. If your eyes aren’t as sharp as they once were and you are experiencing some discomfort, then it is time to visit a doctor with the right expertise for a proper checkup.
Residents who live anywhere in or near Arizona can make appointments and visit one of the Arizona Retinal Specialist facilities. The local clinics have a team of experts to help you get the treatment you need. With Intraocular Pressure Measurement services, we can properly assess your current eye health and give you an accurate diagnosis. Fill out a form now or call us to set your appointment.
