Frequently Asked Questions

What is a Visual Field Test?

Visual field testing (also known as perimetry) is commonly used to assess peripheral vision in each eye to assess for glaucoma.

Why is Visual Field Testing important?

Visual field testing allows for early detection of glaucoma. If detected early glaucoma can be halted, saving people from irreversible vision loss. Glaucoma is the most common cause of preventable blindness globally.

My visual field is normal: does that mean my eyes are completely healthy?

It is great to have a normal visual field test, but it does not necessarily mean you do not have any eye conditions. In early cases of glaucoma, the visual field test may be normal. It is important to note that visual field testing is complementary to clinical evaluation and other tests by an eye care clinician. We do not recommend visual field testing without care from an eye care clinician.

My visual field is abnormal: does that mean I have glaucoma?

Not necessarily. There are many causes of an abnormal visual field test, of which glaucoma is just one. The test can often reveal spurious false results, and there may be nothing wrong with your eyes; so it is best to get checked by an eye care professional.

What do the results mean?

The visual field test generates a map of your peripheral vision over a 10 or 24 degree area of vision. The Sensitivity displays show how sensitive your vision is at each testing spot. The top sensitivity map shows the raw scores at each spot, while the lower image shows a greyscale impression of the sensitivity scores. Your raw sensitivity scores are compared to age-matched normal: to generate your Total Deviation displays. Because some conditions (such as incorrect spectacle correction or cataract) can affect the overall sensitivity of the visual field, this can be subtracted out to reveal focal areas of any defects: this generates the Pattern Deviation displays. For both Total Deviation and Pattern Deviation there are two maps. The higher map (with numbers) shows the comparison between the age-matched normal and your scores, and the lower map (with the dots) shows if there is any major deviation between your test and normal. The significance of any deviation is depicted with dark rectangles instead of dots: the darker the rectangle, the more significant the deviation. The lower Pattern Deviation map is the most important of all the maps which describe your peripheral vision.

How often should I perform visual field testing?

Most patients with glaucoma are advised to have 6 tests within the first 2 years, and thereafter every 6 months; higher risk patients may need testing more frequently (eg 3-4 monthly). People at risk of glaucoma should be tested every 6-12 months.

Is there an overall summary score which shows how well I did?

The best summary score is the VFI, (Visual Field Index), demonstrated at the top of the results page. This shows a percentage, out of 100, of your eye’s overall visual field compared to normal. The other data (MD, PSD) are more technical data used by clinicians to analyse other aspects of the visual field.

I don’t think I did the test very well: are you sure the results are valid?

A visual field test asks people what they can see: it is a subjective test, and this brings room for error and inaccuracy. The test is designed to find the very dimmest spots that you can see. However the test has some clever ways to assess reliability, based on False Positive, False Negative responses and Fixation Losses. If these are too high then the test will be described as “Low Test Reliability”. Otherwise you can be confident it is a high quality test.