How does high
Does high eye pressure always mean glaucoma?
Some people can have IOP that is higher than normal without causing any damage: they may simply need to be monitored. Other people may have an IOP that is within normal limits but nonetheless is causing damage – this is known as low tension glaucoma.
The level of pressure in your eye depends on how well fluid drains out of your eye through a fine mesh known as the trabecular meshwork. For some people, if the meshwork is blocked or working less effectively, the pressure in your eye can rise. To understand more about why this can happen, you can learn more about the causes of glaucoma here.
Glaucoma occurs due to an increase or imbalance in eye pressure resulting in damage to the sensitive nerve fibres at the back of the eye. However, many people are unaware of this type of problem. The changes to the nerve fibres happen slowly and, in most cases, the increase in pressure doesn’t hurt. This is why having regular eye tests is so important, as for most people, it’s impossible to know there might be problems with your eye pressure until it has caused irreversible damage to your eyesight.
For a very small number of people, glaucoma can come on suddenly and painfully. This is called acute glaucoma.
How is eye pressure tested?
As part of your eye test, you will have what’s called a tonometry test to measure the eye pressure. We know that with age the risk of glaucoma can increase. As such, if you’re in your 40s or older, your optometrist will measure your intraocular pressure as part of your routine eye examination. You can learn more about the risk factors for glaucoma development here.
Eye pressure is usually measured by using a machine which measures the pressure using a puff of air. Another method, though, is where you gently touch the tonometer (the instrument used to check your eye pressure) onto the very front surface of the eye. Both methods are completely painless.
A tonometry test gives the optometrist a good measure of the pressure inside your eye. What’s more, if you visit the same optometrist for regular eye examinations they will also be able to see if the pressure in your eyes is rising over time. As so many things can influence intraocular pressure, it’s a good idea to maintain a consistent routine with the same optician so they can monitor progress effectively.
An important side note – the thickness of your cornea (the clear front surface of the eye) can also influence the measurement of the pressure inside your eye. This is due to the fact that the complex mathematics used to calculate eye pressure are based on a cornea of average thickness.
As a result, people with a thicker central cornea are more likely to have an artificially high IOP. Similarly, people with thin corneas may show artificially low IOP readings.
Your optician will recognise this if it is the case. However, it’s worth making sure you’re monitored closely as some of your readings may come back skewed to show artificially high or low IOP.
How often should you have your eye pressure checked?
It entirely depends on how progressed your glaucoma is — from being at risk of glaucoma to more far along in the disease. However, as a minimum for someone aged 40 and over, eye pressure will generally be measured at their regular eye test. Pressures may need to be checked more frequently for people with a family history of glaucoma or if the optometrist has identified other risk factors.
However, as the effect of eye pressure can vary, it’s important for people aged 40 and above, as well as those with a family history of glaucoma, to have visual field tests as well as pressure tests. The optometrist will also examine the back of the eye in order to assess the overall picture of your eye health.
Your optometrist will assess your visual fields by using small dots of light. This allows them to build up a picture to see if intraocular pressure is potentially causing visual field loss. They may also examine the density of the nerve fibre layer in your eyes using an OCT scan. If your optometrist feels that the pressure inside your eyes is unusually high, or it’s high and causing damage to the nerves, they will refer you to a specialist eye doctor known as an ophthalmologist for further investigation.
If you have been referred, there’s no need to worry. Being referred doesn’t always mean that you have glaucoma, just that your optometrist would like to run a couple more tests to make sure. If glaucoma is diagnosed there are a number of ways to treat it successfully.