Visual Fields Testing

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This leaflet is intended to answer some of the questions of patients or carers of patients referred for visual field testing at University Hospitals Sussex NHS Foundation Trust.

What is a fields test?

Visual field tests are designed to document the level of peripheral vision. The test consists of responding every time a flash of light is seen while looking straight ahead.

What is field loss? Why does it matter?

Field loss means that there are areas of your peripheral vision where you do not see as well as you should. The reason we test this is because in certain conditions, especially glaucoma, if left untreated the disease can severely restrict your vision.

How long will it take?

Between three and five minutes per eye but this will vary depending upon your responses and the type of test done.

How often do I need to do it?

Usually every six to twelve months as this has been shown in studies to be a sensible interval for detecting any deterioration.

What is normal?

A normal visual field depends on your age as when we get older the sensitivity of our retina reduces. Your score on the test is matched against a “normal” profile for your age and your results are then graded accordingly.

Is there another way to test for this?

Unfortunately not, although the newer tests are now faster and less tedious than before.
Please speak to the clinician if you are anxious about taking the test, they may be able to help by pausing the test in places or allowing you more time.

Why do I need one?

The most common reason for testing visual fields is for patients with glaucoma or suspected glaucoma although other conditions will also require you to have your fields tested. These might include stroke, droopy eyelids or neurological conditions. The doctor or clinician should be able to tell you why you are having the test.

My vision is fine but I have been told I have field loss: why?

If your central vision is good it is often difficult to notice that you have visual field loss, particularly if it is mild. This is because it tends to come on quite gradually and our brains adapt, especially if the condition only affects one eye.

I have 20 / 20 vision: why can’t I drive?

Although your central vision may be good, the loss of peripheral vision can mean that activities such as driving become incredibly dangerous. Objects in your peripheral vision may be missed and this will effect your ability to perceive hazards. If you are advised by a doctor not to drive no matter how well you believe you can see you should refrain from all driving and inform the DVLA. If you ignore this advice you could be risking your own life as well as the lives of others.

Can cataract cause field loss?

Some other eye conditions such as cataracts can cause you to have field loss. When the doctor interprets the results of the field test they are usually able to decide the cause of any field loss shown.

If I have field loss, do I have glaucoma?

Not necessarily. The fields test is only one part of the assessment to determine your diagnosis.

Why can’t I wear glasses for the test?

Glasses have frames which obstruct your field of view. Instead the machine will calculate the appropriate correction needed for the test, this will then be placed into the machine in the form of a lens.

I already did the test at my optician

Even if you had a very recent test with the optician we would like you to perform this test again at the hospital. This is because the optician may have a different machine or have run a different program and this will not be directly comparable with the last field test you had at the hospital. If you are a new patient the doctor will ask that you to have the fields done here so that they can request exactly which type of test they require.

Why do I have to have one eye covered?

Depending on what we are looking for you may sometimes be asked to do the test with both eyes open. This normally applies to tests which are done for the DVLA. In most other cases we test each eye separately as it is important to know the condition of each eye individually so that we can treat them accordingly.

I was told I did not do the test accurately. Why, and how do you know?

As well as providing information about field loss the machine also records how accurately you have done the test. It can tell if you moved your eye around too much or if you pressed the button when no light was displayed. The clinician performing the test should guide you if you need to try and keep your eye still or if you are pressing at the wrong time. If you do not follow these instructions well, the test becomes invalid and the doctor is not able to use this information to help with the diagnosis. If you have not understood how to do the test, please ask the clinician to stop and explain it again.