What is a visual field test (perimetry)?
A visual field test — also known as perimetry — measures the full extent of your peripheral (side) vision and identifies any blind spots or areas of reduced sensitivity. It is one of the most important diagnostic tools in ophthalmology and optometry, particularly for detecting and monitoring glaucoma, which often attacks peripheral vision first without any noticeable symptoms.
During the test, you look straight ahead into a bowl-shaped instrument and press a button each time you see a small light flash in your side vision. The test is performed one eye at a time and typically takes a few minutes per eye. It is completely painless and non-invasive. The results are plotted as a map of your visual field, showing any areas where your sensitivity is reduced compared to what is normal for your age.
Visual field testing is a routine part of glaucoma monitoring and is often included in a standard NHS eye test if your optometrist identifies risk factors. It is also used to assess fitness to drive (the DVLA has specific visual field requirements), to investigate neurological conditions affecting the visual pathway, and to monitor patients taking certain medications such as hydroxychloroquine (Plaquenil) that can affect the retina.
Who needs a visual field test (perimetry)?
- Anyone being screened or monitored for glaucoma
- People with a family history of glaucoma
- Drivers who need to meet DVLA visual field standards
- Patients with neurological conditions such as stroke, brain tumours, or multiple sclerosis
- People taking medications known to affect the retina (e.g. hydroxychloroquine)
- Anyone who has noticed gaps or missing areas in their vision
What to expect during a visual field test (perimetry)
- 1You sit in front of a bowl-shaped instrument (perimeter) with one eye covered
- 2You focus on a central fixation light and press a button whenever you see a flash of light appear in your peripheral vision
- 3The test is repeated for the other eye
- 4The machine generates a map of your visual field highlighting any areas of reduced sensitivity
- 5Your optometrist or ophthalmologist discusses the results and any further action needed
How much does it cost?
Often included as part of a standard eye test at no extra charge; £15–£30 if performed separately. Free on the NHS when clinically indicated
How often should you have this test?
Annually for glaucoma patients; every 1–2 years for those at risk; as needed for DVLA or neurological assessments