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Wednesday, September 30, 2009

You're blind in one eye, and can’t see out of the other!

Did you know that each of your eyes has a Blind Spot??

There is a spot on the retina of each of our eyes that literally can’t see anything at all. This blind spot is where the optic nerve is and there are no rods or cones there. Now, you normally don’t notice that there is a blind spot anywhere in your field of vision. That’s because your brain is filling in the gaps, so to speak. Try the following experiment to prove it to yourself.

Close your left eye and focus your right eye on the splotch on the left below and then slowly move your head, first towards and then away from the splotches until you notice that the splotch on the right has completely disappeared. Now try the same thing with your left eye focused on the right splotch.

You’ve just found your blind spots!

What’s happening is that the image of the splotch you aren’t focusing on is falling on the optic nerve portion of your eye’s retina – ironically, the optic nerve can’t “see” an image, it can only transmit images. In this case, your brain doesn’t have to do much gap filling actually, because you normally look at things with both eyes, and one eye can always see the spot that the other eye can’t. But your brain does mesh the two images from each eye into one seemingly seamless image when you are using both eyes.

Note that, in the image above, the Fovea is the point of central focus for the human eye. It is nearby to where the optic nerve is located. But the optic nerve is offset to one side or the other, depending on which eye you're talking about. That's why your blind spot is offset to the right or left.

COOL, eh?
Okay, now for the moment of truth:
How many of you out there didn't know about your blind spots?

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