What to Know About Blind Spots (Scotomas)

Medically Reviewed by Dany Paul Baby, MD on February 28, 2023
Written by Parang Mehta
7 min read

A scotoma is a blind spot in your vision, which is an area you cannot see. Blind spots may be small or large and can be temporary or permanent. A scotoma can also move around to different places in your visual fields.

Vision depends on the cornea and lens in your eye letting in light to form an image on the retina. The retina is a light-sensitive layer covering the back part of the inside of your eyeball. Defective areas on the retina, in the nerves carrying signals from it to the brain, or in the brain area that processes visual signals can all cause some parts of an image to not be perceived.

Scotomas are blind spots—areas you can't see. They appear as dark, very light, blurred, or flickering spots and can be short-lived or permanent. Scotomas often don't cause problems because you have two eyes. You may only notice a scotoma when you close the unaffected eye. Alternatively, you may be able to see only in very bright light or be unable to see some colors because of scotomas.

There are several types of scotomas:

  • Relative scotomas. You can see bright, large objects but not dim, small ones.
  • Absolute scotomas. These prevent vision regardless of light intensity.
  • Positive scotoma. Disorders of the retina may cause the appearance of a black spot in front of the eye corresponding to retinal defects.

A central scotoma is most harmful to vision. Central vision is the most acute part of your vision and allows reading and precision work. Central scotomas make these activities impossible although peripheral vision allows affected people to get around.

One scotoma, or a blind spot in vision, is normal in each eye. This is the optic disk, the place on the retina where the optic nerve starts. There are no rods or cones in this place, and you can't see anything which casts an image at the optic disk.

Your retina, which is a thin layer of neural tissue at the back of your eye, is made up of tiny, light-detecting cells called photoreceptors. When light lands on your retina, it sends electrical bursts through your optic nerve to your brain. Your brain turns the signals into a picture.

The spot where your optic nerve connects to your retina has no light-sensitive cells, so you can’t see anything there. That’s your blind spot.
 

It’s easy to find your blind spot. You can do it in different ways. Here are two examples:

Example 1

Use this image and follow the directions below.

scotoma test

Sit about a foot away from your screen.

To find your right eye’s blind spot:

  • Close your left eye.
  • Stare at the circle.
  • Move closer to the screen, then farther away.
  • Keep doing this until the plus sign disappears.
  • When it disappears, you have found your right eye’s blind spot.

To find your left eye’s blind spot:

  • Close your right eye.
  • Stare at the plus sign.
  • Move closer, then farther away. Repeat.
  • When the circle disappears, you have found your left eye’s blind spot.

Example 2

Use your hands to find each of your blind spots.

To find your right eye’s blind spot:

  • Close your left eye.
  • Hold your left thumb out in front of you, with your arm straight.
  • Look at your left thumb with your right eye.
  • With your left eye still closed, hold up your right thumb.
  • Place your right thumb next to your left thumb.
  • Keep looking at your left thumb.
  • Slowly move your right thumb to the right while looking at your left thumb.
  • When your right thumb disappears, you have found your right eye’s blind spot.

To find your left eye’s blind spot:

  • Close your right eye.
  • Hold your right thumb out in front of you, with your arm straight.
  • Look at your right thumb with your left eye.
  • With your right eye still closed, hold up your left thumb.
  • Place your left thumb next to your right thumb.
  • Keep looking at your right thumb and slowly move your left thumb to the left.
  • When it disappears, you have found your left eye’s blind spot.

To find out how big your blind spot is, move your thumb around, up and down, and to the left and right.

Many disorders can cause scotomas. Temporary scotomas are usually caused by brain disorders such as a seizure, migraine, or reduced blood flow.

Fixed, permanent blind spots can be caused by disorders of:

  • The optic nerve, such as those caused by glaucoma (increased pressure inside the eye) or multiple sclerosis
  • The brain, such as a tumor or stroke
  • The retina, such as a scar or an injury

A blind spot that is growing is often the sign of a retinal detachment. The layers of the retina are separating, and this can cause loss of vision. You will need prompt surgery to prevent blindness in the eye.

Total color blindness is present from birth and is associated with a central scotoma. All colors appear to be greys of different brightness, and central vision is reduced. Macular degeneration, diabetes, and eye injuries can also cause central scotomas.

Scotoma symptoms depend on their location in your visual fields. Central scotomas are the most damaging to vision and daily activities. They affect the central portion of your vision, which you use to see things clearly and read. You may have difficulty recognizing faces and reading regular-sized prints. Seeing color and detail will be difficult, and you may have trouble driving and using computers and devices. You may find that you see best when looking to the side and in dim light.

Peripheral scotomas do not disrupt vision as much unless they're large. You may be unable to see things on the sides and bump into them when walking. Your vision may work best in bright light.

Scintillating scotomas are typical of migraines. They usually appear before the headache and start as a shimmering bright area that prevents seeing a part of the visual field. This bright scotoma has a shimmering character and grows to cover half of your vision. You may see bright spots and rays of various colors. Your vision recovers in about 15 minutes, and the intense headache of a migraine follows. 

High blood pressure, inflammation of the optic nerve, multiple sclerosis, and head injuries can also cause scintillating scotomas.

If your blind spots are hampering your activities and sight, you should consult an ophthalmologist. Before starting scotoma treatment, they will assess your eyes and visual fields. This may involve:

  • A slit lamp examination. An examination of the structures in the front and back of the eye.
  • A fundus examination. Your doctor will instill eye drops to dilate your pupil and use a fundoscope to examine the retina.
  • A visual field test (perimetry). This measures your central and peripheral vision. Perimetry detects scotomas and allows recording of their location and size.

Glaucoma is a case of increased pressure in the eyeball. This damages the optic nerve and causes gradual loss of vision. Certain types of scotomas, detected by visual field testing, help diagnose glaucoma:

  • Relative paracentral scotomas. You can't see dim or small objects, but you can see large and bright objects.
  • Seidel's scotoma. The normal blind spot of the eye extends to arch over the macula.
  • Arcuate scotomas. These also start at the blind spot and arch over the macula to reach the horizontal divide of the visual field.
  • Ring scotomas. These are seen in advanced glaucoma cases. Only the central field and some islands of peripheral vision are preserved.

The treatment of blind spots depends on the cause. Temporary scotomas, such as those caused by migraine, need no specific treatment as they last less than an hour.

Scotomas in the peripheral field don't cause many problems in daily life. Scotomas in the central vision hamper activities but cannot be corrected with glasses, contact lenses, or surgery. You must learn to live with them using devices and strategies to manage the visual deficit.

Some people with central visual loss do better when reading with both eyes (binocular summation), and some when reading with one eye (binocular inhibition).

Your ophthalmologist will help you achieve the best possible vision even if your scotomas can't be cured:

  • If you have a small central scotoma, it may help change the size of things with glasses so that you can see them around the scotoma. Otherwise, it may help enlarge things on your computer screen or screen reader or while printing to let you see and read better.
  • You should use devices like large digit phone keypads, watch faces, talking scales, or clocks.
  • Dimming the lights and wearing sunglasses may help you see better by dilating your pupils.
  • Peripheral scotomas can make walking hazardous. Learning to use a cane is helpful.
  • If your central scotomas make reading difficult, you should learn braille. Using screen readers to learn by listening is another option.