What it measures
Your visual field is everything you can see while looking straight ahead, including your side vision. A field test maps how sensitive each part of it is. It helps find and follow many eye and brain conditions, but its most important use is in glaucoma.
Why it matters in glaucoma
Glaucoma damages the optic nerve fibres that serve side vision first. On a field test, the damage shows as patches of reduced sensitivity, called scotomas. Over time they can join into an arc, and widen towards the centre. You often cannot notice these gaps yourself, because the other eye and the brain fill them in.
Damage that shows on a field test usually cannot be reversed. Repeating the test over months and years shows whether treatment is holding the disease steady.
What the test is like
- One eye is tested at a time; the other is covered.
- You look into a lit bowl and keep your eye on a light in the centre.
- Small spots of light flash at random places around it, some bright, some faint.
- You press a button each time you see one.
Each eye takes several minutes, and the whole test can take 15 to 30 minutes.
Tips for a reliable result
- Keep looking at the centre light. Do not search for the flashes.
- Press only when you are fairly sure you saw a light. Missing faint spots is expected.
- Blink normally, and ask for a pause if you get tired.
- Bring your glasses. Staff fit a lens matched to your prescription.
The first test is often less reliable than later ones, because it takes practice. Your doctor may repeat it before drawing conclusions.
This guide explains; it does not diagnose. Your doctor’s advice about your own eyes comes first.