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11.46: Vision Correction

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Why get an eye exam?

During a routine eye exam, your vision will be evaluated to see if you need glasses or contacts. Also, the eye doctor checks your eyes for diseases that could lead to vision loss.

Vision Correction

You probably know people that need eyeglasses or contact lenses to see clearly. Maybe you need them yourself. Lenses are used to correct vision problems. Two of the most common vision problems are myopia and hyperopia.

Myopia

Myopia is also called nearsightedness. It affects about one third of people. People with myopia can see nearby objects clearly, but distant objects appear blurry. How a person with myopia might see two boys that are a few meters away is shown in Figure below .

Normal Vision, Myopia

On the left, you can see how a person with normal vision sees two boys. The right image shows how a person with myopia sees the boys.

In myopia, the eye is too long. In Figure below , you can see how images are focused on the retina of someone with myopia. Myopia is corrected with a concave lens, which curves inward like the inside of a bowl. The lens changes the focus so images fall on the retina as they should.

Myopia, Hyperopia

The eye of a person with myopia is longer than normal. As a result, images are focused in front of the retina ( top left ). A concave lens is used to correct myopia to help focus images on the retina ( top right ). Farsightedness, or hyperopia, occurs when objects are focused in back of the retina ( bottom left ). It is corrected with a convex lens ( bottom right ).

Farsightedness

Farsightedness is also known as hyperopia . It affects about one fourth of people. People with hyperopia can see distant objects clearly, but nearby objects appear blurry. In hyperopia, the eye is too short. As shown in Figure above , this results in images being focused in back of the retina. Hyperopia is corrected with a convex lens, which curves outward like the outside of a bowl. The lens changes the focus so that images fall on the retina as they should.

In addition to lenses, many cases of myopia and hyperopia can be corrected with surgery. For example, a procedure called LASIK uses a laser to permanently change the shape of the cornea so light is correctly focused on the retina.

Vocabulary

  • concave : Curving inward like the inside of a bowl.
  • convex : Curving outward like the outside of a bowl.
  • hyperopia : Farsightedness.
  • myopia : Nearsightedness.

Summary

  • Vision problems such as myopia and hyperopia can be corrected with lenses that help focus light on the retina.
  • Myopia is corrected with a concave lens, while hyperopia is corrected with a convex lens.

Practice

Use the resources below to answer the questions that follow.

  1. How can the shape of your eyeball cause you to be farsighted? How does this affect your focal point?
  2. How can the shape of your eyeball cause you to be nearsighted? How does this affect your focal point?
  3. How can an irregularly formed cornea affect your vision?
  1. What is myopia? If you had this condition when might you wear glasses?
  2. What is hyperopia? If you had this condition when might you wear glasses?
  3. What is an astigmatism? If you had an astigmatism when might you wear glasses?
  4. At what age do many people start needing reading glasses? What causes this condition?

Review

  1. What is hyperopia, and what type of lens corrects it?
  2. What causes myopia, and what type of lens corrects it?

Image Attributions

Description

Difficulty Level:

At Grade

Grades:

7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Sep 15, 2014
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