Intraocular pressure checks

What is intraocular pressure?

Intraocular pressure (IOP), sometimes also called eye pressure, is an important part of your eye function.

Your eye naturally creates something called aqueous humour, which is responsible for maintain your eye's shape. It is a clear fluid which sits at the front of your eye between your cornea and iris. Your eye is constantly producing new aqueous humour to replace old aqueous humour, which your eye automatically drains. This cycle creates your intraocular pressure and supports your eye health.

An average IOP is considered to be between 10 and 21 mmHg (millimetres of mercury), with most people sitting around 16mmHg.

If your IOP is high, this is called ocular hypertension, which can cause pressure to build up inside your eye. This build up can lead to glaucoma, where eye pressure causes damage to the optic nerve. If your eye pressure is too low, this can cause problems with your retina, cornea and the lens of your eye. This condition is called ocular hypotony.

How is intraocular pressure tested?

IOP is tested using a method called tonometry. There are several different methods of tonometry your eye care professional may use.

Air-puff tonometry

Air-puff tonometry uses a puff of air to briefly flatten a small area of your cornea, measuring your IOP based on the force of the air as it returns from your eye. Some people may experience mild discomfort from the puff of air, but the method is typically very quick and painless.

Rebound tonometry

Rebound tonometry uses a very small probe to lightly touch the cornea of your eye and then measure the rate of deceleration when it bounces back. It is painless and does not require any anaesthesia.

Goldmann applanation tonometry (GAT)

GAT is the most accurate method of testing IOP, which uses a small, flat disc to flatten the cornea temporarily. Your IOP is then calculated based on the force needed to flatten the cornea. Before performing GAT, your eye care professional will administer local anaesthesia and a fluorescein dye using eye drops.

Which method will be used on me?

Several factors will influence how your eye care professional tests your IOP. Air-puff tonometry and rebound tonometry are more commonly used by optometrists and are more portable. If a more accurate measure of your IOP is required, particularly at an ophthalmology clinic, then GAT is more likely to be used.

How often do I need testing?

It is important to detect significant changes or irregularities in IOP early. Your IOP will need checking at different intervals depending on your medical history. Your eye care professional may perform it as part of your routine eye check up every one to three years or may recommend more regular testing to monitor your IOP closely.

Your eye care professional may check your IOP more frequently, or be more likely to use GAT, if you:

• are over 50,
• are experiencing new symptoms or changes in your vision,
• have been diagnosed with a progressive eye condition which requires monitoring, or;
• have a high risk of developing an eye condition.

For more information

Always talk to your eye care professional about the best treatment options for you.