Blind Spot Test - Find Your Visual Blind Spot Online

How to use this tool

1. Choose Left eye (the default) or Right eye. Cover the opposite eye and fixate on the + with the selected eye.
2. Set your viewing distance in centimeters; it defaults to 50 cm.
3. Click Start - the dot moves across the canvas toward the selected eye’s opposite side.
4. Keep your gaze fixed on + and click when the dot disappears, then again when it reappears. Read the approximate center angle and width for that eye.

How the blind spot works

Every human eye has a small region on the retina called the optic disc - the point where the optic nerve exits the eye and where blood vessels enter. Because there are no photoreceptors (rods or cones) at this location, light that falls on the optic disc produces no visual signal. The result is a blind spot in your visual field at roughly 15° from the center of your vision in each eye.

The brain fills in the gap automatically using information from the surrounding retinal area (a process called perceptual interpolation), which is why you don't normally experience a black hole in your vision.

This activity estimates visual angles from the two points where you mark the dot as disappearing and reappearing. It converts canvas coordinates to the canvas's rendered CSS pixels, then uses the entered distance in atan(offset / distance), with distance converted to CSS pixels using 96 CSS pixels per inch. The center angle is calculated from the midpoint of both measured boundaries; angular width is the difference between the angles at those boundaries. The estimate assumes 100% browser zoom and is approximate because screen size, browser zoom, posture, and click timing affect what you see.

Discovery of the blind spot

The blind spot was first described by French physicist Edme Mariotte in 1660. He noticed that a small bright spot placed at a specific position in the visual field of his test subjects seemed to vanish. In France, the blind spot is still sometimes called la tache de Mariotte (Mariotte's spot) in his honor.

How to find your blind spot

1. Choose the Left eye setting (the default) or switch to Right eye. Cover the opposite eye and focus the selected eye on the fixation cross (+).
2. Enter your approximate distance in the viewing-distance control, which defaults to 50 cm. Keep your head and screen in the same position while you test.
3. Click Start, keep looking at +, and mark when the moving dot disappears and reappears.
4. Review the approximate center angle and width for the selected eye.

This demonstration is for one eye at a time. Its results depend on the distance, the rendered canvas size, display scaling, and your timing; they do not measure a complete visual field.

Why don't we normally notice it?

Two reasons make the blind spot invisible in everyday life:

• Binocular vision: With both eyes open, the blind spot of each eye falls in a region that the other eye can see. The two visual fields overlap, completely covering the gap.
• Perceptual filling-in: Even with one eye closed, the visual cortex interpolates a seamless continuation of the surrounding texture or color into the blind spot region. This is the same mechanism that makes the dot disappear rather than leaving a black void.