Blind Spot Test

How to find your blind spot

1. Calibrate the screen with a bank card (below the chart) so the angles are right. On a phone, turn it sideways.
2. Sit at the distance you choose, measured from your eye to the screen: 50 cm is about an arm's length.
3. For the right eye, cover your left eye and look at the black cross on the left with your right eye. Do not look at the red dot.
4. Press Start measuring. The dot moves slowly away from the cross. Press space (or tap the chart) the moment it disappears, and again when it comes back.
5. Choose Left eye: the cross moves to the right side. Cover your right eye and repeat.

What the results mean

The page shows where the dot vanished and came back, as an angle from the point you were looking at. In a typical eye:

• the blind spot starts at about 12 to 13 degrees from where you look, towards the ear;
• it ends at about 18 degrees, so its centre is near 15 degrees;
• it is about 5 to 6 degrees wide and a little taller than it is wide, roughly the size of your fist at arm's length seen 15 degrees off to the side.

A result a degree or two away from these numbers is usually a wrong distance, a missing calibration, a wandering eye or a late press. Repeat the test once or twice and take the average. The Classic mode shows the textbook picture: a dot placed at 15.5 degrees that vanishes when you are at the right distance. Fill-in shows a line with a gap at the blind spot that looks unbroken, because the brain fills the hole with what surrounds it.

Why we have a blind spot

The light-sensitive cells of the retina sit behind a layer of nerve fibres. All those fibres leave the eye together through one hole, the optic disc, to form the optic nerve, and there is no room for rods or cones there. The disc is about 1.5 mm across and lies about 15 degrees to the nose side of the centre of the retina, so in what you see the blind spot falls about 15 degrees to the ear side.

You never notice it for two reasons. With both eyes open, each eye covers the other's blind spot. And with one eye closed, the brain fills the gap with the colour and pattern around it, which is why the fill-in demo looks like an unbroken line. The French physicist Edme Mariotte first described the blind spot in 1660.

Blind spot or visual field loss?

The normal blind spot is small, in the same place in both eyes, and you do not notice it in daily life. Gaps you do notice are different. Missing patches, a shadow or curtain, a part of the page that disappears while reading, or bumping into things on one side can be a sign of glaucoma, retinal problems, optic nerve disease or a stroke. A visual field test at an optometrist or eye clinic maps your whole field properly. Seek urgent care for sudden loss of part of your vision.

Common problems and fixes

The dot never disappears

Make sure the other eye is fully covered and you keep looking at the cross, not following the dot. Check the distance: if you sit much closer or further than chosen, the blind spot falls somewhere else on the screen.

The screen says it is too narrow

The dot must travel about 20 degrees. Turn a phone sideways, use full screen, or choose a shorter distance.

My angles look too big or too small

Calibrate the screen with a bank card, keep the browser zoom at 100%, and measure the distance to your eye with a tape.