Blind spots in your vision can come from a wide range of causes, from the completely normal anatomy of your eye to serious conditions that need urgent attention. Every human eye has one natural blind spot where the optic nerve connects to the retina, but new or noticeable blind spots, whether temporary or persistent, usually signal something worth investigating.
The Blind Spot Everyone Has
Every eye has a built-in blind spot about 15 to 16 degrees off-center from where you’re looking. This is the optic disc, the small area where the optic nerve exits the retina. No light-detecting cells exist in that spot, so it literally cannot see. You don’t normally notice it because your brain fills in the gap using information from the surrounding area and from your other eye. This natural blind spot is roughly the size of a small oval and sits slightly to the outside of your central vision in each eye.
This is not the kind of blind spot most people are worried about when they search for answers. If you’re noticing a new dark patch, a blank area, or a spot where things seem to disappear, something else is going on.
Migraine Aura: The Most Common Temporary Cause
If your blind spot appeared suddenly, lasted less than an hour, and came with shimmering lines or zigzag patterns, you likely experienced a migraine aura. These temporary visual disturbances tend to start near the center of your vision and spread outward. You might see a blank spot outlined by a flickering ring or circle, along with shimmering spots or wavy lines that float across your field of view.
A migraine aura typically develops within an hour before headache pain begins and resolves within 60 minutes. Some people get the visual symptoms without any headache at all, which can be especially confusing. These episodes are caused by a wave of electrical activity spreading across the brain’s visual processing area, not by damage to the eye itself. They’re unsettling but not harmful on their own, though recurring episodes are worth mentioning to your doctor to rule out other causes.
Glaucoma: Slow, Silent Peripheral Loss
Glaucoma is one of the most common causes of permanent blind spots, and it’s particularly dangerous because you won’t notice the damage until it’s well advanced. The condition damages the optic nerve, and the blind spots it creates start at the edges of your vision and slowly creep inward. Most people don’t realize anything is wrong because the brain compensates for early peripheral losses.
The only modifiable risk factor for glaucoma is eye pressure, though the disease can also develop in people with perfectly normal pressure (called normal-tension glaucoma). An abnormality in the eye’s drainage system causes fluid to build up, which puts pressure on the optic nerve. The damage is irreversible, which is why routine eye exams that include a pressure check are so important, especially after age 40. Treatment focuses on lowering eye pressure to slow or stop further nerve damage.
Macular Degeneration: Blind Spots in the Center
If you’re over 50 and noticing blank or dark spots right in the middle of your vision, macular degeneration is a likely suspect. This condition damages the macula, the tiny central area of the retina responsible for sharp, detailed vision. People with macular degeneration can often still see in their peripheral vision but struggle to read, recognize faces, or see anything they look at directly.
About 90% of cases are the dry form, where small protein deposits called drusen accumulate under the macula and gradually thin it out. Vision loss with dry macular degeneration tends to be slow, and most people retain some central vision. The wet form is less common (about 10% of cases) but far more aggressive. Abnormal blood vessels grow under the retina and leak fluid, creating a bulge in the macula that can quickly destroy central vision.
A simple at-home tool called an Amsler grid can help you monitor changes. Hold the grid 12 to 15 inches from your face with your reading glasses on, cover one eye, and stare at the center dot. If any of the surrounding lines look wavy, blurry, dark, or blank, that’s a sign of macular changes. Repeat with the other eye. Doing this daily helps catch progression early, when treatment for the wet form is most effective.
Diabetic Retinopathy: Dark Spots From Leaking Blood Vessels
Chronically high blood sugar damages the tiny blood vessels that nourish the retina. Over time, these vessels weaken, and in advanced stages the eye tries to grow replacement blood vessels that are fragile and poorly formed. When these new vessels leak blood into the clear gel filling the eye (a vitreous hemorrhage), you may see dark spots or squiggly lines floating across your vision. A small bleed produces a few floaters. A larger one can block a significant portion of your visual field.
This is a major reason why people with diabetes need annual dilated eye exams. The retinal damage often progresses without obvious symptoms until bleeding occurs, and early detection allows treatment before vision loss becomes severe.
Stroke and Brain Injuries
Your eyes may be perfectly healthy, but if the brain areas that process vision are damaged, you can lose large portions of your visual field. Stroke is the most common cause, accounting for nearly 70% of cases of hemianopsia, a condition where you lose half of the visual field in both eyes. If a stroke affects the right side of the brain’s visual cortex, you lose the left half of your vision in both eyes, and vice versa.
This type of vision loss feels different from an eye problem. It’s consistent, affects the same side in both eyes, and often comes alongside other stroke symptoms like weakness, confusion, or difficulty speaking. Over half of people with stroke-related visual field loss experience some spontaneous recovery within the first month, though the degree varies widely.
Optic Neuritis: Inflammation of the Optic Nerve
Optic neuritis causes a blind spot or general dimming of vision that develops over several days, often with pain when you move your eyes. Colors may look washed out or duller than normal, sometimes dramatically so. It’s caused by inflammation of the optic nerve and is sometimes associated with multiple sclerosis, though it can occur on its own. Vision in the affected eye may drop significantly during the worst of the episode, but many people recover substantial vision over weeks to months.
Warning Signs That Need Emergency Care
Some blind spots are medical emergencies. Retinal detachment, where the light-sensitive tissue peels away from the back of the eye, can cause permanent vision loss if not treated within hours. The classic warning signs are a sudden burst of new floaters, flashes of light in one or both eyes, and a dark shadow or “curtain” that spreads across part of your vision. If you experience any combination of these, get to an eye doctor or emergency room immediately. Early repair has a much higher success rate than waiting.
In general, any blind spot that appears suddenly, grows rapidly, or comes with flashing lights, pain, or other neurological symptoms (numbness, weakness, difficulty speaking) warrants urgent evaluation.
How Blind Spots Are Diagnosed
Eye doctors map your blind spots using visual field tests, also called perimetry. The most common version is a static perimetry test (like the Humphrey test), where you look into a bowl-shaped machine and press a button each time you see a small light flash in different parts of your peripheral vision. The machine builds a detailed map of where your vision is intact and where it drops off. Another approach, kinetic perimetry, involves a technician moving an object around while you report when it appears.
These tests are painless and take about 10 to 20 minutes per eye. The resulting map helps your doctor determine whether the pattern of vision loss points to a retinal problem, optic nerve damage, or something in the brain. Combined with a dilated eye exam and sometimes imaging, the cause of most blind spots can be identified with confidence.