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What Is a prism correction on my eyeglasses, part 1

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Did you ever see the classic Mel Brooks comedy “Young Frankenstein”?

If not, watch it as soon as possible. It’s hilarious.Go ahead, we’ll wait.

OK, you’ve watched the movie. Were we wrong? I mean, the “Puttin’ on the Ritz” dance? It doesn’t get any funnier than that.

Now that you’ve seen this comedy classic, let’s talk about one character in particular: Igor, played by Marty Feldman.

There’s a reason his name is not pronounced “EE-gore” but “EYE-gore,” and it’s not just because Dr. Frankenstein’s name is pronounced “FRONK-en-steen”.

It’s that when Feldman is onscreen, you can’t take your eyes off his eyes, which do not point in the same direction. The actor had a condition called exotropia. Exotropia? What’s that? A space colony? No. Good try, though.

Exotropia is a form of strabismus.

“OK wise guy,” we hear you saying. “What are exotropia and strabismus?”

We thought you’d never ask.

Let’s start with strabismus.

Strabismus is a condition in which the eyes are not aligned with each other because not all of the eyes’ muscles are working together. Here’s how it works: There are six muscles in each eye that control the eye’s movements. These are called “extra-ocular muscles”.

They enable your eyes to rotate in all directions, which is necessary for you to be able to properly express sarcasm.

But sometimes, these six extra-ocular muscles are not perfectly coordinated with each other, meaning you’ve got a slacker in the bunch. If this is the case, your two eyes don’t look at the same thing at the same time. Just like Marty Feldman’s Igor.

Exotropia, as we said, is a form of strabismus. The prefix “Exo” means “to exit” or to “move out”. Try it when you want to get rid of (and befuddle) a bad roommate:

“It’s exotropia time, loser.”

Exotropia is the type of strabismus Marty Feldman had, as a result of a botched operation in his youth, causing his eyes to turn outward (exo). A more common way to refer to this is “walleyed”.

The other form of strabismus, in which one or both eyes turn inward, is called esotropia. This is more commonly referred to as being “cross-eyed”.

Strabismus hampers the ability of the brain to fuse the two images that the eyes see into one 3-D image, which creates depth perception. Along with a lack of depth perception, a person with strabismus may also experience double vision.

In the optical world, double vision is known as diplopia. If you have diplopia, you may see two images, or one blurry one.

Fortunately, eyeglasses with a prism embedded in the lenses can correct this. However, diplopia can also be caused by having one blind eye or an eye with minimal vision. Unfortunately, this can’t be corrected by a prism alone; eye surgery on the extra-ocular muscles may be necessary, too.

In part two, we will examine how the prism correction on eyeglasses can correct diplopia.

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