http://www.ck12.org Chapter 1. Human Biology
1.46 Vision Correction
- Explain how lenses correct vision problems.
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 who 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
Myopiais also called nearsightedness. It affects about one third of people. People with myopia can see nearby
objects clearly, but distant objects appear blurry. The picture below shows how a person with myopia might see two
boys that are a few meters away (Figure1.89).
In myopia, the eye is too long. Below, you can see how images are focused on the retina of someone with myopia
(Figure1.90). Myopia is corrected with aconcavelens, which curves inward like the inside of a bowl. The lens
changes the focus, so images fall on the retina as they should.
Farsightedness
Farsightedness is also known ashyperopia. 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. This results in images