Tonometry: How is Eye Pressure Measured?

The older we get, the more susceptible we are to acquiring eye conditions that can affect our lives significantly. But sometimes, the solution to this problem is not just getting a pair of reading glasses. Some conditions may be more severe, in which case calls for a trip to a specialist. One common exam that these experts will have you take is a Tonometry test.

Tonometry is an eye test that measures your eye pressure. Patients who experience intense eye pain or redness should be tested because their eye pressure may be above normal.

Normal eye pressure ranges from 12-22 mm Hg. If it is greater than 22 mm, Hg is considered higher than normal. Knowing your eye pressure is important for specialists to determine if you have ocular hypertension or glaucoma. These two conditions can affect your daily life if left untreated. Once experts properly diagnose you, they can proceed to help treat your condition.

Who Needs a Tonometry Test?

Those with symptoms like the gradual loss of peripheral vision, blurred or tunnel vision, and severe eye pain may need to take the test as these are glaucoma symptoms. Physical signs may include reddening and halos around the eyes.

Also Read: Glaucoma: A Common Disease That Can Cause Blindness

Most patients who experience these symptoms are forty years and older, non-Caucasian, and have a family history of glaucoma. Others can include those whose eyes had previously been injured, had been diagnosed with other eye conditions, or have other health conditions such as diabetes and high blood pressure.

Types of Tonometry

Applanation Tonometry

This type of test involves tools and direct contact with the eyes to get results. Generally, a slit lamp with a forehead and chin support is used. A flat-tipped cone comes into contact with your cornea to see how much force is needed to flatten it. There are many types of applanation tonometry, which are the following:

  • Goldmann Tonometry

The Goldmann Tonometry test is the most common test for eye pressure measurement and is held as the reference standard. This type of applanation tonometry uses the device called Goldmann Tonometer, which is an instrument that is based on the Imbert-Fick law. 

Doctors would administer eye-numbing drops onto your eyes before getting you ready for the machine. This is the procedure where you stay still while the machine presses against your corneas and the doctor makes adjustments to get your eye pressure measurements. It may seem intimidating at first because something is literally pushing against your eye as you watch. But you can ease your apprehensions. Because of the anesthetic and fluorescein, you won’t be able to feel a thing.

  • Perkins Tonometry

Like Goldmann Tonometry, Perkins Tonometry uses an instrument that will come into contact with the eyes. It functions like the Goldmann method, also using the Imbert-Fick law. It also presses against your corneas to test eye pressure. The only difference is that this device is handheld. 

Only trained professionals are allowed to use this device. Patients have to keep their eyes wide open for the checkup duration for the specialist to examine the eye with the device properly.

  • Pneumotonometry

Pneumotonometry is when the doctor uses a pneumonometer to estimate eye pressure measurements. It is an applanation instrument, but it uses some aspects of indentation tonometry, a type of tonometry that follows the principle that the soft eye will sink when a force or weight is applied. The pneumatonometer uses a 5mm diameter silicone tip with a piston at the end that rides on a stream of air. Its accuracy is similar to the Goldmann Tonometer.

Air-Puff Tonometry

If a patient is squeamish about taking a direct contact type of test, another test doesn’t require direct contact with the eye. In air-puff tonometry, no machine presses against the patient’s cornea to measure eye pressure. 

Instead, this tonometer releases air that gradually increases pressure to measure your mmHg. An infrared beam is also shown directly off your cornea. When the cornea starts to flatten due to the air pressure, the infrared light beam will reflect at a different angle. 

Puff tonometry isn’t the most used type of eye test because its accuracy can be slightly questionable. It could give an overestimation of your intraocular pressure (IOP) measurements. 

Rebound Tonometry

Rebound tonometry is a new type of eye pressure test most suitable for children. It is a non-invasive and nonthreatening way to measure IOP of children without causing serious damage. It also does not require the administering of general or topical anesthesia. 

This new technology is promising as most doctors wouldn’t risk giving other types of exams to children who don’t have visible symptoms. Rebound tonometry used as a screening test is generally done by pediatric ophthalmologists and less by general ophthalmologists. If glaucoma runs in your family and you would like to test your kids or grandchildren for it, it’s best to take them to a pediatric ophthalmologist.


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.


NOTICE TO USERS is not intended to be a substitute for professional advice, diagnosis, medical treatment, or therapy. Always seek the advice of your physician or qualified health provider with any questions you may have regarding any health symptom or medical condition. Never disregard professional medical advice nor delay in seeking professional advice or treatment because of something you have read on