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Tonometry
Tonometry measures the pressure inside your eye, an important check for glaucoma.
Quick answer
Tonometry: what it is and what the results mean
Tonometry measures intraocular pressure — the fluid pressure inside the eye. It can be done with a puff of air or by gently touching the eye’s surface after numbing drops.
- Why it is done: It is used to screen for and monitor glaucoma, a condition where raised eye pressure can damage the optic nerve and sight, and to assess other conditions affecting eye pressure.
- Understanding results: The result is an eye pressure reading.
What it is
Tonometry measures intraocular pressure — the fluid pressure inside the eye. It can be done with a puff of air or by gently touching the eye’s surface after numbing drops.
Why it is done
It is used to screen for and monitor glaucoma, a condition where raised eye pressure can damage the optic nerve and sight, and to assess other conditions affecting eye pressure.
What to expect
For the air-puff method, a quick puff of air is directed at your eye, which can feel surprising but is painless. For the contact method, numbing drops are used and a small probe gently touches the eye’s surface for a moment.
Understanding the results
The result is an eye pressure reading. A higher-than-normal pressure raises the concern of glaucoma and prompts further tests, though pressure alone does not diagnose it, and some people develop glaucoma with normal pressure.
Good to know
Risks and limitations
It is safe and quick. Eye pressure varies through the day and a single reading can be misleading, so it is interpreted alongside other checks such as the optic nerve and visual field.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Tonometry: frequently asked questions
Does the eye pressure test hurt?
No. The air-puff version is painless though it can make you blink, and the contact version uses numbing drops so you do not feel the probe gently touch your eye.
Does normal eye pressure rule out glaucoma?
Not entirely. Some people develop glaucoma with normal pressure, which is why the optic nerve and visual field are also checked. Pressure is one important part of the assessment.
Related tests
Other other investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Relevant royal college / professional body
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