Humphrey Visual Fields
The 'Gold standard' visual field test
Change analysis as well as screening
Error detection and correction
The Humphrey Visual Field is an industry standard test which allow us to look for defects in the sensitivity of the eye. For example, the central vision of the eye may be good, but the periphery of the visual field may be severely damaged. It is important to detect change in the visual field in order to maintain the function of the eye. As a good eye is able to compensate for poor vision in the other eye, the effects of visual field damage are often unnoticed by the patient until there is significant damage to the vision. The Humphrey visual field tests is designed to pick up the earliest changes to the function of the eye.
The patient places their chin on a chin-rest and fixes their eye on a light or "fixation point" ahead of them. The test works by displaying flashes of light around the bowl that has a fixed background light level. The machine aims to find the dimmest light that the eye is able to detect at various locations in the visual field.
How Long Does This Take?
The most common test asked for by consultants is the 24-2 SITA standard and this normally takes about 10 minutes per eye. Other tests may take slightly longer. We recommend that you allow at least 45 minutes for a 24-2 and an hour for a 30-2.
Your Visual Field Questions and Comments
Visual field testing can tell us a lot about the vision and the condition of the optic nerves. However it can seem quite a challenging test, especially if you're new to it. Here are a few of the questions and comments that come up frequently regarding visual fields:
Are some of the lights brighter than others?
With the Humphrey Visual Fields Test, we are trying to find the very faintest light that you can see at each point on the screen. The flashes vary in brightness and some will be very faint. Ultimately, the machine is trying to find the faintest light that you can see at each point. There are some brighter lights thrown in as well.
Sometimes I think I'm imagining the lights
As the machine is trying to detect the very faintest light that you can see, sometimes it's difficult to be sure what you've seen. Do press if you think you've seen a light but don't if you haven't.
How can the test be accurate if I'm not sure what I've seen?
The Humphrey machine gradually works out what you can and can't see. It will start off with some bright lights to make sure that you can see them properly. As the test goes on, it gradually reduces the brightness of the lights at each point until you can't see them. This is randomised, so the lights will vary in brightness from one to the next. The machine will keep testing until it had got a consistent value for each point.
I missed a light / I pressed by accident
Don't worry - the machine checks each point several times during the test. If you miss a light then the machine will come back with a slightly brighter one at that point next time. If you press by accident, the light will be fainter next time. The test is interactive and it will keep going until it's happy that it has all the data it needs.
Should I keep my eye open under the patch?
Generally it's better to keep both eyes open. If you close one eye, it tends to make it more difficult to keep the other wide open. You may miss some of the upper lights if the eye being tested isn't wide open enough.
When should I blink?
Some people worry about blinking during the test as they may miss some of the lights. However, as the test can last several minutes, this doesn't help in practice. The machine retests each point several times so if you do miss any then that shouldn't affect the results. If you try not to blink for too long it can make the eyes watery. You then risk missing some of the lights because of that instead.
My eyelids droop a bit...
Sometimes we are using the visual field test to see what effect the eyelids are having on the peripheral vision, so that's not a problem. If we are investigating other conditions, such as glaucoma, then the eyelids may cause an error in the results. We can put a small piece of microporous tape on the eyelid to help if this is a problem.
Should I wear glasses?
This will depend on the type of test: For the Humphrey tests then we will normally use the reading prescription. If the glasses are suitable then we can use those but otherwise we can use a small lens to sharpen up the vision while you do the test. Varifocals, tinted glasses and reading glasses with small frames will cause problems. By measuring the strength of either your reading, distance or varifocal glasses then we can calculate which lens to use for the test. For binocular tests (where both eyes are tested at the same time) glasses may or may not be used depending on the frames. For some tests a lens may be used to test the central points, then removed to test the peripheral ones.
DVLA Visual Fields
We are unable to perform visual field testing for the DVLA. Please contact them directly for further information about their testing procedure. For further information about vision requirements for driving, please click here