Visual Field Test: The Examination & Results

What is a visual field test and what do the results show?

A visual field test is an eye examination that gives very useful information to ophthalmologists as well as neurologists. It is a non-invasive test that shows us the extent of the field that each eye sees separately. It can therefore reveal eye diseases as well as neurological conditions related to the parts of the brain involved in vision. If there is an abnormal finding, further tests may be needed to investigate the cause.

Page contents

1. What is a visual field test and what do the results show?
2. Which are the most common conditions that require visual field testing?
3. How long does a visual field test take?
4. Is any preparation needed for the test?
5. Is the test painful?
6. How exactly is the test carried out?
7. Can the test ever not be carried out?
8. How large is the normal visual field
9. Why we do not notice visual field loss
10. Types of test
11. How the results are read
12. What the different patterns of damage mean
13. Visual fields in glaucoma: diagnosis and monitoring
14. Other situations where the test is needed
15. Tips for a reliable result
16. How often the test is repeated
17. What to do if you find the test difficult
18. How visual fields fit with the rest of the examination
19. Visual field and driving
20. Screening: who should have it
21. Questions worth asking after the test
22. The test step by step, from arrival to result
23. Myths about visual fields
24. Frequently Asked Questions about Visual Field Testing

A visual field test can detect scotomas, or blind spots, and identify any restriction in peripheral vision. Such a restriction may be a sign of glaucoma, a condition that needs particular attention.

Good vision depends mainly on the retina, the optic nerves and the brain. When a disease starts to develop in any of these tissues, vision starts to become restricted. The way in which vision is restricted gives us useful information and significant help in reaching the right diagnosis.

Which are the most common conditions that require visual field testing?

• Glaucoma
• Ocular hypertension
• Optic nerve conditions such as multiple sclerosis.
• Brain disorders such as strokes or tumours
• Pituitary disorders

How long does a visual field test take?

The test usually takes no longer than 10 minutes. With good cooperation from the patient and our experience, it may take even less.

Is any preparation needed for the test?

None at all. In very rare cases, drops may be needed to dilate the pupil (mydriasis), which are put in at the clinic.

Is the test painful?

No, the test is carried out from a distance and nothing touches the eye. A patch is placed over the eye that is not being tested.

How exactly is the test carried out?

After entering the patient’s details into the programme, we place a cover in front of one eye. The patient rests their chin on the special support and looks at a red light. When the test starts, white lights flash briefly inside the device, which has a dome. The patient’s task is to press a button every time they see a light, without taking their eyes off the central red light.

Can the test ever not be carried out?

Very, very rarely. Usually, people with very low vision or significant clouding of the optical media (cornea, lens, etc.) find it difficult and the results are not particularly reliable.

How large is the normal visual field

When we look steadily at a point in front of us, we do not only see that point. At the same time we perceive movement and objects around it, over a range that for each eye reaches about 90 degrees outwards, 60 inwards, 50 upwards and 70 downwards. Sharpness is greatest in the centre, where the macula focuses, and gradually decreases towards the periphery.

Every normal eye has a small “blind spot”, slightly outwards from the centre. It corresponds to the point where the optic nerve leaves the eye and there are no photoreceptors. We do not notice it, because the brain “fills it in” and because the other eye covers that area. The visual field test records it as normal, and it also serves as a reference point for the reliability of the measurement.

Why we do not notice visual field loss

Many patients are surprised when the test shows large defects, even though they themselves “see well”. The reason is that, when the damage starts in the periphery and develops slowly, the brain completes the image and the other eye covers the gaps. Central vision, which we use for reading, remains intact for a long time. So in glaucoma, the patient may lose a significant part of the field before noticing anything. This is why the visual field test is so valuable: it measures something the patient cannot perceive themselves.

Types of test

Automated static perimetry

This is the most widely used method. Points of light of different intensity appear at fixed positions inside a dome and the patient presses a button whenever they see one. The computer finds, at each point, the faintest light the eye can see. There are different programmes: some test the central 24 or 30 degrees, which is the standard for glaucoma, while others focus on the central 10 degrees with more closely spaced points, for damage near the centre.

Kinetic perimetry

A light target moves from the periphery towards the centre and the patient indicates the moment they notice it. This maps out the boundaries of the field across its full extent. It is useful for neurological conditions, for advanced damage and for patients who find the static test difficult.

Faster screening programmes

For a quick screening check, there are shorter programmes that test whether there is any damage without measuring it in detail. If something suspicious is found, a full test follows.

How the results are read

The printed visual field result looks complicated, but the ophthalmologist reads it in a specific order:

• Reliability indices: First, we check whether the test is reliable. It records how many times the gaze moved away from the centre, how many times the patient pressed the button without a light appearing, and how many times they missed a light they had seen before. If the values are poor, the test is repeated.
• Greyscale map: A visual representation in which dark areas show reduced sensitivity. It is easy to understand, but it is not enough on its own for a diagnosis.
• Probability maps: These compare each point with normal people of the same age and show how likely a finding is to be abnormal.
• Global indices: Numbers that describe the overall loss of sensitivity and how localised or diffuse it is. They are mainly used for monitoring over time.

What the different patterns of damage mean

The shape of the loss in the visual field acts as a “signature” of the condition. It helps the doctor understand where the problem lies, in the eye, the optic nerve or the brain:

• Arcuate defects and nasal step: Typical of glaucoma, they follow the path of the retinal nerve fibres.
• Central scotoma: A “spot” in the centre, which appears in macular diseases or in inflammation of the optic nerve.
• Enlarged blind spot: May be related to swelling of the optic disc.
• Bitemporal hemianopia: Loss of the outer half of the field in both eyes, often caused by pressure on the optic chiasm, for example from a pituitary tumour.
• Homonymous hemianopia: Loss of the same side of the field in both eyes, which indicates damage behind the chiasm, such as after a stroke.
• Peripheral constriction: Narrowing of the field from all sides, as in advanced glaucoma or inherited retinal diseases.

Visual fields in glaucoma: diagnosis and monitoring

In glaucoma, visual fields have a double role. In diagnosis, they confirm that the damage to the optic nerve has a functional consequence. In monitoring, they show whether the disease has stabilised with treatment or is still progressing. Because measurements naturally vary from day to day, a single test is not enough to decide that there is deterioration. A series of tests over time is needed, analysed statistically to show the rate of progression.

Visual fields are combined with optical coherence tomography (OCT), which measures the thickness of the nerve fibres. OCT often detects changes earlier, in the early stages, while visual fields are more useful for monitoring advanced disease. Together they give the most complete picture.

Other situations where the test is needed

• Neurological problems: After a stroke, in pituitary tumours, in optic neuritis or in idiopathic intracranial hypertension.
• Medication monitoring: Hydroxychloroquine, used in rheumatic diseases, requires an annual check of the central 10 degrees together with OCT after a certain number of years of treatment.
• Drooping eyelid: To document that the eyelid restricts vision, before functional blepharoplasty.
• Retinal diseases: Such as retinitis pigmentosa and vascular occlusions.
• Driving licence and occupational assessments: In some categories, certification of an adequate visual field is required.

Tips for a reliable result

• Come well rested. Tiredness reduces attention and “spoils” the measurements.
• Bring your reading glasses or let us know your prescription. The device needs the right correction.
• Keep looking at the central point. Do not search for the lights with your eyes.
• Press the button only when you are sure you have seen a light. It is normal not to see many of them.
• If you get tired, say so. The test can be paused for a few seconds.
• Blink normally, so that your eyes do not dry out.

It is also well known that a person’s first ever test is often less reliable, because the patient is learning the procedure. This is why, if the first test shows findings, it is usually repeated before any conclusion is drawn.

How often the test is repeated

How often depends on the reason for the test and on the severity of the condition:

• Newly diagnosed glaucoma: Several tests in the first two years, often every 4 to 6 months, so that the rate of progression can be established quickly.
• Stable glaucoma: Usually once or twice a year, together with OCT.
• Suspected glaucoma or high pressure without damage: A yearly test for comparison.
• Neurological conditions: According to the instructions of the neurologist or neurosurgeon.
• Hydroxychloroquine: A yearly check after the first years of treatment, or earlier if there are risk factors.

What to do if you find the test difficult

Quite a few people feel anxious during a visual field test, because they are afraid they are “failing” when they do not see a light. There is no failing: the device is designed to show lights that are at the limit of vision, which nobody sees every time. This is what makes the test so sensitive.

If you have a neck or back problem, let us know before the test starts, so that the height can be adjusted properly. If the vision in one eye is very low, or if your hands shake, the ophthalmologist may choose a different programme or method. For older people or children, shorter programmes are preferred so that they do not get tired.

How visual fields fit with the rest of the examination

No visual field result is assessed in isolation. The ophthalmologist compares it with the appearance of the optic nerve on fundoscopy, the OCT, the intraocular pressure and the medical history. A defect that does not match the appearance of the nerve may be caused by clouding from a cataract, tiredness, the wrong glasses or an eyelid covering part of the field. On the other hand, a defect that matches the nerve damage exactly has great diagnostic value. In some cases, findings that point to a problem in the brain lead to a referral for an MRI scan.

Visual field and driving

For safe driving, it is not enough to read road signs well. We need to notice in good time a pedestrian stepping into the road from the side or a car pulling out of a junction. This is what the peripheral visual field makes possible. People with advanced glaucoma, hemianopia after a stroke or severely drooping eyelids may have a restricted field without knowing it.

The law sets minimum visual field requirements for issuing and renewing a driving licence, with stricter criteria for professional drivers. The visual field test is the objective way to document whether these are met. If you have a condition that affects your visual field, discuss it with your ophthalmologist before renewing your licence.

Screening: who should have it

A visual field test is not necessary for everyone. However, it is recommended as part of the assessment for people at increased risk of glaucoma: those with a family history of glaucoma, high intraocular pressure, a thin cornea, high myopia or a suspicious appearance of the optic nerve on fundoscopy. It is also recommended for people who take steroids long term or medicines that require eye monitoring. After a basic eye examination, the ophthalmologist will tell you whether you need the test.

Questions worth asking after the test

• Was the test reliable or does it need to be repeated?
• Is there a defect, and where?
• Does it match the appearance of the optic nerve and the OCT?
• Has anything changed compared with the previous test?
• When should I repeat it?

The test step by step, from arrival to result

1. Preparation: We ask about your prescription and, if needed, place the appropriate trial lens in front of the eye being tested. The other eye is covered with a soft patch.
2. Position: You sit comfortably, rest your chin and forehead on the support and we adjust the height.
3. Instructions and practice: We explain what you will see and do a short practice run before the measurement starts.
4. Measurement: This usually takes 4 to 8 minutes per eye, depending on the programme. The test is monitored throughout, and if your gaze wanders, we remind you.
5. Second eye: After a short break, the same procedure is repeated.
6. Result: The result is available immediately and is discussed with the doctor, together with the other findings.

Myths about visual fields

• “If I see well, my visual field is normal.” Good central vision does not rule out loss in the periphery, especially in glaucoma.
• “If I didn’t see many lights, the test went badly.” The device deliberately shows very faint lights that nobody sees. This is normal.
• “One test is enough for ever.” In chronic conditions, the value of the test lies in comparing it with previous ones.
• “Visual fields have been replaced by OCT.” The two tests complement each other: one shows structure, the other shows function.
• “The test is tiring and difficult for older people.” Modern programmes are short and adapt to the patient. Most older people complete it without any difficulty, with a few breaks where needed.

Because pupil dilation is not required, you can drive and go back to work straight afterwards. If you have had visual field tests at another centre, bring the results so that they can be compared with the new measurement and your progress can be seen accurately. The comparison is more reliable when the same test programme is used at every visit. To book a visual field test, call 210 677 0007.

Frequently Asked Questions about Visual Field Testing

Medically reviewed by: Dr. Vasileios Skouteris MD, FEBO