Every healthy eye has a small patch where it detects nothing at all, and you can find yours in under a minute with a pen and a scrap of paper. Draw a cross and a dot a few inches apart, cover one eye, stare at the cross with the other, and slowly bring the paper toward your face. At one distance the dot vanishes, because it now lands exactly on that patch, where the optic nerve leaves the eye. In daily life you never see a hole, because your brain quietly paints over the gap with a guess.
The Step-by-Step Blind Spot Test
Draw a small cross and a solid dot about 3 inches apart on a card or a piece of paper, with the cross on the right. Hold the card at eye level, about an arm’s length away.1Exploratorium. Blind Spot
Start with your left eye:
- Close or cover your right eye.2Exploratorium. Blind Spot
- Look straight at the cross with your left eye. You can still see the dot off to the side.3Exploratorium. Blind Spot
- Keep staring at the cross while you slowly bring the card toward your face.4Exploratorium. Blind Spot
- At one distance the dot disappears, and as you keep moving closer it reappears.5Exploratorium. Blind Spot
Then switch. Close your left eye and look directly at the dot with your right eye. This time the cross disappears and reappears as the card comes closer.6Exploratorium. Blind Spot Each eye has its own blind spot, on the outer side of whatever that eye is looking at.
Glide the card toward you over several seconds, because the dot only vanishes over a short stretch of the approach. With marks about 3 inches apart, that usually happens somewhere around a foot from your face. When the dot goes, stop and hold still for a moment to be sure it’s truly gone and not just faint. Then move slowly in and out across that spot a few times to learn the small range of distances where the dot is invisible.
When it works, the dot doesn’t turn black. The paper’s color replaces it, as if it had never been drawn.
The whole test depends on your eye staying put. Stare at the center of the cross and resist glancing at the dot, which you can only sense from the corner of your eye. If you catch yourself looking at it, its image moves off the blind spot and it reappears, so just return to the cross and carry on. Blink normally and keep your head still so that only the card moves.
If the dot never seems to vanish, the usual culprits are these:
- Wrong side: with the left eye open, the cross belongs on the right; with the right eye open, it belongs on the left.
- Peeking: the covered eye can still see the dot and spoil the effect.
- Speed: moving the card fast skips right past the narrow distance where the dot disappears.
- A weak mark: make the dot dark, solid, and about the size of a pencil eraser, since a tiny faint mark is hard to judge.
- Spacing: a gap between cross and dot that is too narrow or too wide changes the distance at which the dot falls in the blind spot, so try a slightly different one.
Why the Dot Disappears
The back of your eye is lined with light-sensing cells, the retina. But the optic nerve, the nerve that carries signals from the eye to the brain, has to exit through the retina at one spot, the optic disc. That disc has no light-sensing cells, so anything whose image lands there goes unseen. The gap exists because in human eyes the nerve wiring sits in front of the light-sensing cells and must pass through the retina to leave.
The fibers run along the retina’s inner surface, gather together, and dive out at one point, and there is simply no room for sensing cells in that bundle. The blood vessels that feed the retina enter and leave through the same spot, which adds to the area that can’t sense light.
The disc is a small round patch, and the retina around it works normally, so the loss is limited to a tiny area. Doctors can see it when they look into your eye, where it appears as a pale round spot with vessels radiating from it. It’s part of normal anatomy, not a defect or a sign of damage.
The disc sits toward the nose side of each retina, not at the center. Because images flip inside the eye, that puts the blind spot on the outer side of your view. That’s why the cross and dot go side by side, with the dot toward the ear side of the open eye. Moving the card changes where on the retina the dot’s image lands. Only at one distance does it fall right on the disc.
Not every eye is built this way. In octopus eyes the light-sensing cells point toward the light, and each sends its own fiber straight to the brain.7PubMed Central. The Eye of the Common Octopus (Octopus vulgaris) Their nerve leaves from the back, so no gap is needed in the sensing layer.
Why You Never Notice the Gap
Each eye’s blind spot falls on a part of the scene the other eye can see. The two eyes view the world from slightly different positions, and the brain combines both images into one view, so the gap in one eye is covered with real information from the other. With both eyes open there’s no missing patch at all.
Even with one eye shut, you don’t see a black patch. A shape crossing the blind spot is seen as complete.8PubMed. An investigation into perceptual completion in blind areas of the visual field The brain uses the color and shape around the spot to decide what to paint in, whether a plain color, dots, or a bar.9PubMed. Preattentive and cognitive effects on perceptual completion at the blind spot One explanation is that the brain predicts what should be there from patterns it has learned in ordinary scenes, like lines that keep going.10PubMed Central. Predictive Coding: A Possible Explanation of Filling-In at the Blind Spot
You can watch this happen. Draw a straight line through where the dot was, and at the vanishing distance the line looks unbroken.
The brain has only the surroundings to go on, so it paints a best guess of what likely continues. That’s why a small object sitting wholly inside the blind spot, with nothing similar around it, can go unseen even though it’s really there.
The brain doesn’t simply stretch the surrounding vision to close the gap; positions around the spot stay true.11PubMed Central. Cortical representation of space around the blind spot12PubMed. Two-dot alignment across the physiological blind spot A straight line passing near the gap still looks straight.
Where Your Blind Spot Is and How Big It Feels
The blind spot sits about 15 degrees off to the side of the point you’re looking at.13PubMed Central. Fine-scale measurement of the blind spot borders14PubMed Central. Highly accurate retinotopic maps of the physiological blind spot in human visual cortex It also sits slightly below eye level, roughly 1 to 2 degrees.15PubMed Central. Highly accurate retinotopic maps of the physiological blind spot in human visual cortex16PubMed Central. Impact of Natural Blind Spot Location on Perimetry Because it sits only slightly low, the marks can sit side by side and don’t need to be stacked.
It is about 5 degrees wide and 6 degrees tall.17PubMed Central. Highly accurate retinotopic maps of the physiological blind spot in human visual cortex Its edges fade gradually, so vision is slightly weakened in a zone about 6 degrees wide around it.18PubMed Central. Fine-scale measurement of the blind spot borders Near the rim the dot may fade, shimmer, or blink in and out as tiny eye movements shift its image. That’s normal.
Degrees are easier to grasp with your hand. At arm’s length, your thumb covers about 2 degrees, so the blind spot is roughly two to three thumb-widths across and sits about seven thumb-widths to the side of where you look.
Other Ways to Try the Test
You can draw a cross and dot on a screen, stare at the cross with one eye, and lean slowly toward it. The dot vanishes at a distance of about 1 to 1.2 times the screen’s height.19PubMed Central. Home-based visual field test for glaucoma screening comparison with Humphrey perimeter Home vision-test software uses this exact trick to check that you’re sitting at the right distance and keeping your eye still.20PubMed Central. Home-based visual field test for glaucoma screening comparison with Humphrey perimeter
A phone screen is small, so you hold it close and place the cross and dot a few centimeters apart, which lets the dot fall in the blind spot at a comfortable distance. Keep the background plain and move slowly.
The blind spot was first described by French scientist Edme Mariotte in the 1600s.21PubMed. Edme Mariotte (1620-1684): Pioneer of Neurophysiology He stuck two large paper circles on a wall about two feet apart, the right one a bit lower, covered his left eye, and looked at the left circle from about nine feet away. The right circle disappeared.22The Linda Hall: Science Library and Arboretum. Scientist of the Day – Edmé Mariotte, French Physicist
You can vary the paper version too. Use two different shapes, like a star and a circle, so it’s easy to tell which one vanished. Swap eyes, and swap which shape you fix on, to test both.
When a Blind Spot Is a Sign of an Eye Problem
Finding your blind spot in this test is normal; everyone has one. But swelling of the optic nerve, called papilledema, makes the blind spot larger and can narrow side vision.23Harvard Health. Optic Nerve Swelling (Papilledema) Without treatment it can progress to a smaller field of vision and eventually blindness.24Harvard Health. Optic Nerve Swelling (Papilledema) In some very nearsighted eyes, changes around the optic disc can enlarge the blind spot.25PubMed Central. Enlarged Blind Spot Linked to Gamma Zone and Peripapillary Hyperreflective Ovoid Mass-Like Structures in Non-Pathological Highly Myopic Eyes26PubMed Central. Anatomic Peculiarities Associated with Axial Elongation of the Myopic Eye If you’re nearsighted and your spot seems larger, mention it at your next eye exam.
Swelling of the optic nerve often comes from raised pressure inside the skull, so it can come with headaches and sometimes brief dimming of vision. Early on it may cause no clear symptoms, which is why an eye doctor often finds it by looking at the back of the eye. Because the cause can be serious, new symptoms like these deserve medical attention.
A normal test gives the same result each time: the dot vanishes over a short range of distance and returns. A spot that seems much bigger than before, or one that vanishes over a much wider range of distances, may mean something has changed in the eye or optic nerve. One odd test isn’t a diagnosis, since poor technique often explains a strange result, so repeat it carefully first.
Missing patches you notice with both eyes open, or headaches with blurred or dimming vision, are worth an eye exam. See an eye doctor promptly rather than relying on a home test.
Missing areas elsewhere in your vision matter for safety. Gaps from eye disease that sit beside the center of vision make drivers more likely to miss pedestrians or react too late.27PubMed Central. Hazard Detection by Drivers with Paracentral Homonymous Field Loss: A Small Case Series28PubMed Central. Driving with Central Visual Field Loss II: How Scotomas above or below the Preferred Retinal Loss (PRL) Affect Hazard Detection in a Driving Simulator
A home test shows the normal spot but can’t measure small changes accurately, and normal results at home don’t rule out early eye disease. Eye doctors use a field test: you stare at a central point while small lights flash in different places, and you press a button each time you see one. That maps your whole field of vision and can reveal gaps you never noticed, because the brain’s patching hides them in daily life.