Glaucoma
What is eye pressure, and what is a normal reading?
Eye pressure, or intraocular pressure, is the pressure of fluid inside the eye, measured in millimetres of mercury. Most healthy eyes read between about 10 and 21 mmHg. Pressure is the main treatable risk factor for glaucoma, but a normal reading does not exclude glaucoma and a high reading does not by itself confirm it.
How it is measured
Applanation tonometry is the reference standard. After a numbing drop and a dye, a small probe gently touches the surface of the eye at the slit lamp. It is quick and should not hurt. Air puff and handheld instruments are useful for a quick check but are less precise, so borderline readings are usually confirmed by applanation.
Corneal thickness affects readings. A thick cornea can make pressure read higher than it truly is, and a thin cornea can make it read lower while also being an independent risk factor for glaucoma.
Why the number moves
- Pressure varies through the day, often highest in the morning hours
- It changes with body position, and rises when you hold your breath or strain
- Steroid tablets, inhalers, injections, eye drops and skin creams can raise it
- It can rise after eye injury, inflammation or certain eye surgery
- A single reading is a snapshot, so trends across visits matter more than one number
High pressure without glaucoma, and glaucoma without high pressure
Some people have pressure above 21 mmHg with a healthy optic nerve and normal fields. This is called ocular hypertension, and it is monitored, sometimes treated, because it raises the risk of developing glaucoma. Others develop typical glaucoma damage with pressures that always read normal, known as normal tension glaucoma. This is why pressure is interpreted together with the optic nerve, OCT and visual field findings.
What treatment aims for
When glaucoma is present, your ophthalmologist sets a target pressure, lower than where damage occurred, based on how advanced the condition is. Treatment is then adjusted until that target is reached and held steady.
Frequently asked questions
- Can diet or exercise lower eye pressure?
- Regular moderate aerobic exercise may lower pressure slightly, and it is good for general eye health. It is not a substitute for prescribed treatment. Avoid breath holding during heavy lifting and head down yoga postures if you have advanced glaucoma.
- Does high blood pressure cause high eye pressure?
- They are separate measurements and one does not directly set the other, although blood pressure and its treatment can influence blood flow to the optic nerve. Both are worth controlling.
Concerned about these symptoms?
Arrange an eye examination with our consultant ophthalmologist in Garki, Abuja.
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Related answers
- Which tests are used to diagnose glaucoma?
- What is glaucoma?
- How do glaucoma eye drops work?
- What does glaucoma screening involve?
Return to all glaucoma answers.