Intraocular pressure (IOP)

Intraocular pressure, also known as IOP (intraocular pressure), is the pressure exerted by the fluid inside your eyeball on the walls of the eye. This fluid, known as aqueous humour, is constantly produced in the eye and drains away through small channels. The balance between production and drainage determines the eye pressure.

Normal intraocular pressure is usually between 10 and 21 mmHg (millimetres of mercury), although this value can vary from person to person. Intraocular pressure can fluctuate throughout the day and is influenced by factors such as posture, physical exertion and the time of day.

Excessively high intraocular pressure can, over time, cause damage to the optic nerve and the retina, which can lead to loss of peripheral vision. Intraocular pressure that is too low is less common, but can also cause problems. Eye pressure is measured using a tonometer, an instrument used by opticians, optometrists or ophthalmologists during an eye examination.

Elevated intraocular pressure is a risk factor for glaucoma, but not everyone with high intraocular pressure goes on to develop the condition. Conversely, glaucoma can also occur in people with normal eye pressure. That is why regular monitoring of eye pressure and the health of the optic nerve is important, particularly from a certain age or if you are at increased risk.

When is intraocular pressure measured?

Measuring eye pressure is part of a comprehensive eye examination and is often carried out as standard during check-ups from the age of 40 onwards. Your ophthalmologist or optometrist will also measure your eye pressure if you have any symptoms, are at increased risk of glaucoma, or as part of a check-up for a known eye condition.

What can affect intraocular pressure?

Various factors can affect eye pressure, either temporarily or chronically. Physical exertion can lower pressure, whilst certain postures (such as leaning forwards for long periods) or wearing tight collars can increase it. Medication, heredity, age and certain eye conditions also play a role.

Have you noticed any changes in your eye pressure?

In most cases, you won’t notice if your eye pressure is too high or too low. There are usually no symptoms until damage has already occurred. That is why regular check-ups are important. In the event of a sudden, sharp rise in eye pressure, symptoms such as pain, blurred vision, headaches or nausea may occur, but this is rare and requires immediate medical attention.

What if your eye pressure is abnormal?

If you have any symptoms or concerns, or if a measurement has shown that your intraocular pressure is abnormal, please have it assessed by your optician, optometrist or ophthalmologist. They can carry out further tests and determine whether and what follow-up steps are necessary. Self-diagnosis or self-treatment is neither possible nor advisable when it comes to eye pressure.