How Tonometry Eye Pressure Test Works

Tonometry is a test to measure the pressure inside your eyes, referred to as intraocular eye pressure (IOP). Measuring your eye pressure is an important part of a comprehensive eye examination. If your eye pressure becomes higher than normal, you may be at risk for developing eye diseases such as glaucoma. High eye pressure can damage the delicate nerve fibers in the back of your eye, sometimes resulting in blindness.

A tonometer is an instrument that determines intraocular pressure by measuring the resistance of your cornea to indentation. Your eye doctor or healthcare provider may use one of several methods to measure the pressure inside your eyes.

Intraocular pressure testing for glaucoma
Westend61/ Getty Images

Goldmann Tonometry

The most common tonometer that eye care practitioners use is the Goldmann applanation tonometer. A Goldmann tonometer is usually attached to a slit lamp microscope. Anesthetic eye drops are instilled into your eyes, followed by a small amount of fluorescein dye. A cobalt blue light then illuminates the flurorescein and the tonometer. A small probe is gently pressed onto your eye, indenting the cornea. The pressure that the cornea pushes back onto the tonometer is measured in millimeters of mercury, giving your eye doctor or healthcare provider a number to record and compare to from year to year.

Non-Contact Tonometry

Non-contact tonometry (NCT) is commonly referred to as the "air puff" test. Many people prefer this type of tonometry because it does not involve touching the eye. Instead, a gentle puff of air is used to flatten the cornea. Some studies show that NCT tonometry is not as accurate as Goldman tonometry but NCT provides a very useful and speedy way of measuring eye pressure in children or sensitive adults.

Electronic Tonometry

Electronic tonometry refers to a handheld, mobile device that your eye doctor or practitioner can carry from room to room to check eye pressure. Resembling a writing pen, the mobile tonometer is gently and quickly applied to your cornea. Your healthcare provider will probably obtain about three readings in order to obtain an accurate measurement. Electronic tonometry is not as reliable or as accurate as Goldman tonometry but is extremely handy for a busy practitioner.

Schiotz Tonometry

Schiotz tonometry is a form of indentation tonometry. An indentation tonometer measures eye pressure by measuring the depth of deformity caused by a small metal plunger as it rests on the cornea. Modern eye care practitioners don't use indentation tonometry as much as the other kinds but it is sometimes used in more remote setting.

Normal eye pressure differs between people. If your eye pressure is higher than normal, your risk of developing glaucoma may be increased.

Was this page helpful?
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Eye Institute. Causes of glaucoma.

  2. Yilmaz I, Altan C, Aygit ED, et al. Comparison of three methods of tonometry in normal subjects: Goldmann applanation tonometer, non-contact airpuff tonometer, and Tono-Pen XL. Clin Ophthalmol. 2014;8:1069-1074. doi:10.2147/OPTH.S6391

  3. Aziz K, Friedman DS. Tonometers-which one should I use? Eye (Lond). 2018;32(5):931-937. doi:10.1038/s41433-018-0040-4 

  4. Hark LA, Myers JS, Pasquale LR, et al. Philadelphia Telemedicine Glaucoma Detection and Follow-up Study: Intraocular Pressure Measurements found in a population at high risk for glaucoma. J Glaucoma.

Additional Reading
  • Eskridge, J Boyd, John Amos and Jimmy Bartlett. Clinical Procedures in Optometry, pp 221-237. JB Lippincott Company.

  • Kurtz, Daniel and Nancy B. Carlson. Clinical Procedures for Ocular Examination, pp 289-300. The McGraw-Hill Companis, Inc.