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5.60: Vision Problems and Corrective Lenses

Created by: CK-12

If you’ve ever had your vision checked, you’ve no doubt been asked to read an eye chart like the one in this cartoon. The patient in the cartoon must be having trouble making out the letters in the second row of the chart, because he asks the doctor for a hint (in the style of a popular TV game show). The patient clearly has a vision problem.  

Problems with Vision

Many people have problems with their vision , or ability to see. Often, the problem is due to the shape of the eyes and how they focus light. Two of the most common vision problems are nearsightedness and farsightedness, which you can read about below. You may even have one of these vision problems yourself. Usually, the problems can be corrected with contact lenses or lenses in eyeglasses. In many people, they can also be corrected with laser surgery, which reshapes the outer layer of the eye. For a video about vision problems, go to this URL: http://www.youtube.com/watch?v=ekSGbXt4XdI

Nearsightedness

Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects appear blurry. The Figure below shows how it occurs. The eyeball is longer (from front to back) than normal. This causes images to be focused in front of the retina instead of on the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they fall on the retina instead of in front of it.

Q: Sometimes squinting the eyes can help someone see more clearly. Why do you think this works?

A: Squinting may improve focus by slightly changing the shape of the eyes. When you squint, you tighten muscles around the eyes, putting pressure on the eyeballs.

Farsightedness

Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects appear blurry. It occurs when the eyeball is shorter than normal. (see Figure below ) This causes images to be focused in a spot that would fall behind the retina (if light could pass through the retina). Hyperopia can be corrected with convex lenses. The lenses focus images farther forward in the eye, so they fall on the retina instead of behind it.

Q: Joey has hyperopia. When is he more likely to need his glasses: when he reads a book or when he watches TV?

A: With hyperopia, Joey is farsighted. He can probably see the TV more clearly than the words in a book because the TV is farther away. Therefore, he is more likely to need his glasses when he reads than when he watches TV.

Summary

  • Many people have vision problems. Often, the problem is due to the shape of the eyes and how they focus light. Two of the most common vision problems are nearsightedness and farsightedness.
  • Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects appear blurry. The eyeball is longer than normal, focusing images front of the retina. Concave lenses can correct the problem.
  • Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects appear blurry. The eyeball is shorter than normal, focusing images behind the retina. Convex lenses can correct the problem.

Vocabulary

  • vision : Ability to sense visible light and see.

Practice

Answer the questions on the vision test at the following URL. Be sure to have your answers marked. http://www.bbc.co.uk/scotland/learning/bitesize/standard/physics/health_physics/quiz/light_and_sound/

Review

  1. Compare and contrast myopia and hyperopia.
  2. Explain how lenses can be used to correct vision problems.

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Description

Difficulty Level:

Basic

Grades:

7 , 8

Date Created:

Nov 01, 2012

Last Modified:

Aug 22, 2014

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