What's a normal eye pressure? And why the number isn't everything

When we measure the pressure inside your eye, you’ll get a number in mmHg, and almost everyone immediately wants to know: is mine normal? It’s a fair question. But eye pressure is one of those numbers that’s genuinely useful and easy to misread, so let me give you the honest version.

The usual normal range

For most people, intraocular pressure (IOP) sits between about 12 and 21 mmHg. Readings in that band are commonly called normal. Above roughly 21 is often labelled “raised”, and is one of the things we keep an eye on.

That’s the simple part. Here’s where it gets more honest.

A “normal” number doesn’t rule out glaucoma

This surprises people: you can have eye pressure in the normal range and still have glaucoma. It’s called normal-tension glaucoma, where the optic nerve is being damaged even though the pressure reads under 21. This is exactly why we don’t diagnose glaucoma from pressure alone, and why we also scan the optic nerve (OCT) and test your side vision.

A “high” number doesn’t always mean glaucoma

The reverse is also true. Some people run pressures a little above 21 for years with a perfectly healthy optic nerve, a situation we call ocular hypertension. It raises your risk and means you should be watched, but on its own it isn’t glaucoma. We look at the whole eye, not just the gauge.

Why your number can wobble

Eye pressure isn’t a fixed figure. It can vary:

• Through the day, it’s often higher in the morning.
• With corneal thickness, a thick cornea can make the reading look higher than the true pressure, and a thin one lower.
• Between machines and visits, which is why we look at your trend rather than fixate on one reading.

So how should you read your number?

Treat the pressure as one important clue, not the verdict. What actually protects your sight is the full picture, pressure plus the health of your optic nerve plus your visual field, tracked over time. A single reading, high or low, is the start of a conversation, not the end of one.

Worried about your eye pressure, or have a family history of glaucoma? See how we assess and monitor glaucoma or message us on WhatsApp for a baseline check.