In myopia, the eye is too long. As shown inFigure20.22, this results in images being
focused in front of the retina. 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.
Figure 20.22: The eye of a person with myopia is longer than normal and as a result, images
are focused in front of the retina (top); concave lens is used to correct myopia to help focus
images on the retina (bottom)(Left)Normal Vision (Right)Myopia. ( 7 )
Hyperopia
Hyperopiais also called farsightedness. 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 11b, 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 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.Lesson Summary
- Humans can normally see both distant and close-up objects clearly, and we also see in
three dimensions and color. - Light entering the eye is focused by the lens on the retina, which sends messages to
the brain through the optic nerve. - Visible light is electromagnetic radiation that can be detected by the human eye.
- Vision problems such as myopia and hyperopia can be corrected with lenses that help
focus light on the retina.