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Q & A: Seeing Clearly Now

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Most recent answer: 10/22/2007
I’m doing a project on light at school and my friend and I chose to explain how glasses help short and long sighted people see clearly in connection to light. Could you help me?
- Amy Kleynhans (age 14)
Westerford High School, South Africa
Let's first talk about why people need glasses sometimes. In order to see things clearly, the light must hit our eyes at a certain point which is called the retina. In the front of our eye, we have a lens that bends the light so that it hits the retina in just the right way so that we see a clear image. Many people have lenses that aren't quite the right shape to do the job perfectly. Without the right lens, the image we see becomes very very fuzzy.

Now on to lenses. There are 2 main types of lenses, convex and concave. The convex lens is wider in the middle and narrow on the edges. And the concave lens is wider at the edge than it is in the middle. Each of these lenses will bend light. Concave bends light out and convace bends it in. Here's the neat part. When you put too lenses next to each other, their effects add up. So if you have a convex lens and a concave lens that are both the same power, they totally cancel each other out.

So we put those 2 things together and get glasses. The optometrist will check your eyes and find out which type of lens (concave or convex) you need. Then he figures out what power lens, when added to the strength of the one in your eye, gives the clearest vision.

So when you look through glasses, you are looking through 2 different lenses on each eye, but it acts just like you had the right lens in your eye to begin with.


(published on 10/22/2007)

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