a person having tonometry

Your eyes are the windows to the world, and maintaining their health should be a top priority. One essential aspect of good eye health is monitoring eye pressure, and that’s where tonometry comes into play. This vital test helps detect and prevent serious eye conditions, such as glaucoma, by measuring the pressure inside your eyes, also known as intraocular pressure (IOP).

Key Takeaways

  • Tonometry is an essential part of eye care, measuring and monitoring eye pressure levels to detect the risk of glaucoma.
  • Various techniques are used to measure intraocular pressure (IOP), including Goldmann applanation, non-contact tonometry, and electronic tonometry.
  • Regular tests should be conducted in individuals at risk for glaucoma or over 40 years old. Results must take into account corneal thickness for accurate interpretation by a healthcare provider.

The Importance of Tonometry

Tonometry plays a pivotal role in detecting and monitoring eye pressure levels, as untreated high pressure can cause optic nerve damage and glaucoma. Glaucoma, a serious ocular condition, can lead to vision impairment if not managed properly. Tonometry helps in detecting the risk of developing glaucoma by measuring eye pressure, which is instantly recorded by an instrument.

Tonometry tests are typically completed within a minute or two, using an instrument that calculates eye pressure. Given the importance of maintaining a normal eye pressure range and the quick, non-invasive nature of the test, it’s easy to see why tonometry is a key component of eye care.

Eye Pressure and Intraocular Pressure (IOP)

Eye pressure, also known as intraocular pressure (IOP), is the force exerted by the fluid inside the eye. Good eye health hinges on maintaining a healthy IOP, as it fosters proper functioning of the optic nerve. Typical intraocular pressure values in a healthy human eye usually range from 10 to 21 mmHg, which represents the actual eye pressure.

There are three primary methods for assessing ocular pressure:

  1. Determining the force required to flatten a portion of the cornea (the most accurate method measures eye pressure)
  2. Utilizing a handheld device fashioned in the shape of a pencil
  3. The noncontact technique (air puff)

Each method has its own advantages and disadvantages, which will be discussed in more detail in the following sections.

Identifying Candidates for Tonometry

Senior person, happy on the phone.

Individuals at risk for eye disease, experiencing symptoms of glaucoma, or over the age of 40 should undergo regular tonometry tests to detect glaucoma early. These tests help monitor the efficacy of glaucoma treatment, ensuring that any fluctuations in eye pressure are promptly addressed.

Removing contact lenses before a tonometry test is necessary to prevent permanent staining. In fact, not doing so can permanently stain contact lenses. Routine eye care should incorporate regular eye exams and tonometry tests as they help in preventing clinical complications. Early detection of potential eye issues can lead to timely treatment and prevention of more severe complications.

Tonometry Techniques and Procedures

There are various tonometry techniques available, including Goldmann applanation, non-contact tonometry, and electronic tonometry, each with its own procedure and accuracy level.

The subsequent subsections provide a detailed analysis of these techniques, including and hedges clinical procedures, elaborating on their procedures, advantages, and disadvantages.

Goldmann Applanation

Goldmann applanation tonometry is considered the gold standard for measuring IOP, involving a small probe gently touching the eye’s surface. This method ascertains the force required to flatten a region of the cornea, making it the most precise technique for measuring eye pressure.

The procedure for Goldmann applanation involves the following steps:

  1. Administering anesthetic eye drops and a small amount of dye into the patient’s eyes
  2. The patient placing their chin on a chin rest and their forehead against a bar
  3. The provider lifting up the patient’s upper eyelid
  4. Moving a blue light across the eye to allow the dye to be seen under illumination

A small probe attached to the slit lamp is moved close enough to the patient’s eye to just touch the cornea, gently indenting it, and the tonometer measures the force necessary to flatten the cornea. Patients should remove contact lenses and inform their healthcare provider of any eye conditions or glaucoma history before the test.

Non-Contact Tonometry

Non-contact tonometry, also known as air-puff tonometry, offers a touch-free alternative for measuring IOP, using a puff of air to measure eye pressure. Although accurate, this method may overestimate pressure, making it less reliable than Goldmann applanation for correct pressure measurement.

During the test, the patient’s chin is placed on a chin rest, and a device similar to a slit lamp emits a rapid pulse of air onto the cornea. The force required to applanate the cornea is detected, and this data is used to gauge the pressure inside the eye.

Although patients may feel slight pressure on the eye due to the air puff, this non-invasive method is often preferred for its reduced dependence on the operator and no risk of infection transmission.

Electronic Tonometry

Electronic tonometry is a quick, handheld method for measuring IOP but is less reliable than Goldmann applanation. This technique involves using a handheld device, similar to a writing pen, that instantly records eye pressure by making contact with the cornea. The instrument calculates eye pressure with ease, providing a convenient option for eye care professionals.

The procedure for electronic tonometry requires the use of a handheld, mobile device known as an electronic tonometer, which can be conducted by a technician, optometrist, ophthalmologist, or family doctor. Prior to the procedure, eyedrops may be administered to anesthetize the surface of the eye.

Despite its convenience, electronic tonometry may have lower repeatability and reproducibility compared to Goldmann applanation, making it less accurate in measuring IOP.

Preparing for a Tonometry Test

To prepare for a tonometry test, patients should remove contact lenses, as they may become permanently stained during the test. Additionally, patients should inform their healthcare provider of any eye conditions, previous glaucoma history, and any medications they are taking.

Tonometry measurements can be influenced by certain medications, including:

  • Statins
  • Aspirin
  • Corticosteroids
  • Beta-blockers

Therefore, disclosing any eye health history, including previous conditions or diseases, eye surgeries, medications or eye drops, and any family history of eye diseases like glaucoma, is of utmost importance. This information assists the healthcare provider in evaluating the patient’s risk factors and interpreting the results of the tonometry test accurately.

Interpreting Tonometry Results

Tonometry results are typically available immediately after the test, with a normal range of IOP between 10 to 21 mm Hg. However, one must consider that corneal thickness can influence tonometry measurements. Eyes with thicker corneas tend to yield higher readings, while eyes with thinner corneas generally result in lower readings.

To obtain an accurate pressure measurement, a pachymetry, or corneal thickness measurement, is necessary. If you have questions regarding your test results, it is recommended to discuss them with your healthcare provider.

Abnormal Results and Follow-Up

Abnormal tonometry results may indicate eye conditions such as glaucoma, requiring further testing and follow-up care. Early detection of glaucoma enables the administration of effective treatment before significant damage occurs, underlining the need for regular tonometry tests in maintaining good eye health.

Following abnormal tonometry results, a complete eye exam and glaucoma tests are generally performed to confirm the diagnosis and determine the appropriate course of treatment. If your results are abnormal, it is vital to collaborate closely with your healthcare provider for effective management of your eye health.

Risks and Discomfort Associated with Tonometry

Potential risks associated with tonometry include corneal abrasion, with the level of discomfort varying depending on the method employed. Utilizing numbing eye drops may be beneficial in reducing any pain during the test.

During the applanation method of tonometry, corneal abrasions are a potential risk. To reduce the likelihood of corneal abrasions, patients should:

  • Refrain from any tangential movement across the cornea during the measurement
  • Carefully lift the upper lid without pinning it against the eyeball
  • Utilize numbing eye drops to minimize any discomfort during the test

Glaucoma Detection and Prevention

For early detection and prevention of glaucoma, regular tonometry tests are necessary as they permit prompt treatment and management of eye pressure. The initial indications and manifestations of glaucoma may include:

  • Intense headache
  • Intense ocular pain
  • Foggy or distorted vision
  • Diminishment of peripheral or side vision
  • Perceiving halos around lights
  • Red eyes
  • Nausea
  • Vomiting

It is generally recommended to have regular eye exams, including tonometry tests, at least every two years. For individuals with a higher risk of glaucoma, such as those with a family history of the disease, more frequent exams may be recommended, such as every six months or once per year.

For maintaining good eye health, it is vital to consult with an eye care professional for personalized recommendations.


In conclusion, tonometry is a vital test for maintaining good eye health, detecting and preventing serious eye conditions like glaucoma. With various techniques available, such as Goldmann applanation, non-contact tonometry, and electronic tonometry, it’s crucial to understand the benefits and drawbacks of each method. Regular tonometry tests, especially for those at risk for eye disease or over the age of 40, can ensure timely treatment and management of eye pressure, safeguarding your vision for years to come.

Frequently Asked Questions

What is the normal range for a tonometer?

The normal eye pressure range measured by a tonometer is 10-21 millimeters of mercury (mm Hg). Thick corneas tend to have higher readings, while thin corneas have lower readings. If the reading is higher than 21 mm Hg, it may indicate pre-glaucoma or glaucoma.

How is a tonometry test performed?

Tonometry is a common test for measuring eye pressure. A slit lamp is used to project blue light onto the cornea. Then, a small cone is gently placed on the cornea after numbing eye drops have been administered. Through an eyepiece, the healthcare provider looks at the reading and adjusts the device to get the pressure reading. There is no discomfort associated with this test.

What is the normal eye pressure?

The normal range of eye pressure is between 10 and 21 mm Hg (millimeters of mercury), with the average being around 15 mm Hg. A pressure greater than 21 mm Hg is considered to be ocular hypertension.

How often should I undergo tonometry tests?

It is generally recommended to have tonometry tests at least every two years as part of regular eye exams, especially if you have a higher risk of glaucoma.

What are the potential risks and discomfort associated with tonometry tests?

Potential risks associated with tonometry tests include corneal abrasion, while the level of discomfort can be alleviated with the use of numbing eye drops.


  1. “Tonometry: Purpose, Procedure, and Results.” American Academy of Ophthalmology. https://www.aao.org/eye-health/treatments/tonometry.
  2. “Tonometry: What to Expect During a Glaucoma Test.” Mayo Clinic. https://www.mayoclinic.org/tests-procedures/tonometry/about/pac-20384773.
  3. “Tonometry: Measuring Eye Pressure.” Glaucoma Research Foundation. https://www.glaucoma.org/glaucoma/tonometry.php.
  4. “Understanding Eye Pressure: A Guide to Tonometry.” BrightFocus Foundation. https://www.brightfocus.org/glaucoma/article/understanding-eye-pressure-guide-tonometry.
  5. “Tonometry: What It Is and How It’s Done.” All About Vision. https://www.allaboutvision.com/eye-exam/tonometry.htm.
  6. “Eye Pressure Test: What to Expect.” WebMD. https://www.webmd.com/eye-health/eye-pressure-test.
  7. “Tonometry: How It Works and Why It’s Important.” American Optometric Association. https://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/tonometry.
  8. “Tonometry: A Key Test for Glaucoma.” National Eye Institute. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma/tonometry-key-test-glaucoma.


Photo graph of Dr. Conlon operating with loops on.

Dr. M. Ronan Conlon started his career in the field of ophthalmology at the same time as the development of refractive eye surgery in Canada. In 1996, he brought laser technology to Canada from Germany, which allowed him to perform laser eye surgery before it was available in the United States. With the establishment of the Conlon Eye Institute, Dr. Conlon has performed more than 40,000 refractive procedures and has advanced his expertise in LASIK and refractive cataract surgery.

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