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What is a blind spot?

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Updated October 21, 2010

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: What is a blind spot?
Answer: A blind spot, or scotoma, is an area on the retina without receptors to respond to light. A blind spot is actually a small area without vision. Everyone has a natural blind spot or physiological blind spot in their vision.

Where Is My Blind Spot?

Your blind spot is located on top of your optic nerve inside your eye. The optic nerve is a cable that carries many nerve fibers to the eyeball from the brain. The optic nerve enters the back of your eye and spreads nerve fibers onto the back of the eye to make up the light detecting cell layer (the retina). The small round spot where this cable enters the back of your eye is called the optic nerve head or optic disc. There are no light-detecting cells on this disc. As a result, you have a very small gap in the visual field of each eye.

Why Don't I Notice My Blind Spot?

Each of your eyes has a visual field that overlaps with that of the other to compensate for your blind spot. Your brain is very efficient at using the information from the other eye and other spatial information to "fill in" missing information. Your brain continually makes its best guess as to what is missing.

Find Your Blind Spot

You can find your blind spot by performing the following experiment:
  • Take a piece of paper and mark an X on the left side.
  • About 5 ½ inches away from the X, mark an O. Make sure they are horizontal to each other.
  • Cover your right eye.
  • Look at the O with your left eye. The X should disappear. If it doesn't, move the paper back and forth until it disappears. (You need to be about 1.5 feet away from the paper.)

Abnormal Blind Spots.

A blind spot that you notice in your vision is not normal. If you think that you have one, see your doctor. You may want to prepare for your visit by answering these questions in advance.
  • Does the blind spot come and go?
  • Does the blind spot move in your field of vision?
  • Do you have any other symptoms that occur when you see the blind spot?
  • Are flashing lights associated with the blind spot?
  • Does the blind spot only affect your upper or lower visual field, or does it affect your right side or left side?
  • Does the blind spot only occur in one eye or do you see it in both eyes?
Some blind spots can be caused by a simple migraine, while others can be caused by glaucoma, macular degeneration or retinal detachment. See your eye care professional quickly if think you have a blind spot in your vision.

Source:

Eskridge, J Boyd, John F. Amos, and Jimmy D. Bartler. Clinical Procedures in Optometry, Chapter 49, "Quantitative Perimetry," pp, 447-460. JB Lippincott Company, 1991.

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