Overview

The water-drinking test is a type of stress-test for glaucoma. It helps us assess the changes in eye pressure that might happen during the day. Spikes in eye pressure are associated with an increased risk of developing glaucoma, or of your glaucoma getting worse even if you are already having treatment. 

When you drink a lot of water in a short time, some of the water stays inside your eyes, increasing the eye pressure. The excess water then leaves through the normal drainage channels of the eye.

Depending on how well these channels are working, your eye pressure goes up and then comes back down after a short time. The test is like a 'stress test' for the eye drainage channels, and helps us to understand how well your eyes drain excess fluid.

The test is done as part of the assessments we do in a Phasing Clinic where we normally measure eye pressures over the whole day. However currently, to limit the time you spend in the hospital, we are doing this ‘mini phasing’, water drinking test instead.

Benefits of the test

We need more information about your eye pressures to find out your risk of developing glaucoma, or of it getting worse.

The results of this test will help us decide if:

• you are at risk of developing glaucoma
• you need to start eye pressure-lowering treatment
• we need to change your glaucoma treatment
• you would benefit from laser treatment or surgery

We will also examine your eyes and do other tests, such as a scan of the optic nerve or a visual field test, if needed.

Before the test

Preparing for the test

You should not have anything to eat or drink for at least 2 hours before the test starts.

You can have breakfast, but this must be finished by 7am at the latest, as your test usually starts at around 9am.

If you already use glaucoma drops, continue to use them as normal unless you're told otherwise.

It's very important that you use all your usual morning drops before you leave home. You can also have any other tablets in the morning as usual.

What you need to bring on the day

Please bring:

• your glasses
• a list of your current medicines 
• something to keep you occupied (such as a book or magazine) 

We provide 1 litre of bottled water to be used as part of this test, so there is no need to bring your own unless you prefer to.

During the test

Your vision and usual eye pressure are checked when you arrive. You are then asked to drink between 800mls to 1 litre of water within 5 minutes.

After drinking the water, your eye pressure is checked every 15 minutes at least 3 times. You need to stay in or close to the department during this time. Other eye tests may be done between the eye pressure checks.

You should not have any food or other fluids (including water, coffee or tea) until all the eye pressure measurements have been taken. You can go to the toilet if you need to.

After the test

After the eye pressure checks are done, drops may be used to dilate (widen) your pupils if we need to examine the back of your eyes in detail, or if you need a scan.

Even if the test causes your eye pressure to go up, you will not need to restrict the amount of fluid you drink for the rest of the day. Eye pressure does not change much when you drink normal amounts of water (2 to 3 litres) spread out over a whole day. Avoid drinking large amounts of fluid in a short time, particularly if your glaucoma is advanced or getting worse.

Results of the test 

We will discuss your results with you and decide what treatment might help you. This might involve starting glaucoma treatment, changing your treatment, or discussing laser treatment or surgery.

Your glaucoma risk could also be low and you might not need treatment now, but you might benefit from monitoring for a few years. We also might discharge you back to your optometrist.