Tonometry: What Is It and How Does It Work?

Tonometry is a simple, painless procedure that measures the pressure inside the eye, which is known as intraocular pressure (IOP). The procedure can help your doctor find out if you have glaucoma, a potentially vision threatening condition.


No special preparation is required for tonometry. You may need to remove your contact lenses, and it is important to stay still during the test. Your doctor may apply special drops to your eyes to make the procedure more comfortable.


There are three main types of tonometer used to measure intraocular pressure: non-contact, contact, and air-pulse. The non-contact and air-pulse tonometer measure the eye pressure without touching the eye. The contact tonometer makes direct contact with the eye.

  • Non-contact tonometry: A light is shone into the eye and the reflection from the eye is used to measure IOP.
  • Contact tonometry: A mechanical probe is pressed firmly against the eye to measure IOP.
  • Air-pulse tonometry: A puff of air is blown against the surface of the eye and the reflection is used to measure IOP.

Types of Tonometer

There are several different types of tonometers, including the air-puff, the Goldmann, the Perkins, and the Tono-pen. Your eye care specialist will decide which type of tonometer to use, based on your specific needs.

Risk and Benefits

The risks associated with tonometry are minimal, as the procedure is relatively simple and painless. The procedure only takes a few minutes and can be performed quickly and easily in your eye doctor's office. The benefits are that it can detect signs of glaucoma before it can cause vision loss, possibly preserving your vision.

Why Is It Done?

Tonometry is most commonly used to screen for glaucoma, a condition that occurs when the pressure inside the eye (intraocular pressure) is too high and can potentially damage the optic nerve, leading to vision loss. The procedure is also useful for diagnosing other conditions that affect the eye pressure, such as inflammation, trauma, and congenital defects.

When to Get Tested?

Tonometry is usually recommended for adults over the age of 40, and for those at high risk of glaucoma, such as those with a family history of the condition or those with certain eye conditions. Other people who need to be screened include people who are very nearsighted, people who take certain medications, and people who have eye disorders such as diabetes mellitus or cataracts.