11.49: 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. About one of every two people end up needing some sort of vision correction during their lifetime.
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 is 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 (Figure below).
In myopia, the eye is too long. Below, you can see how images are focused on the retina of someone with myopia (Figure below). 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.
Generally, nearsightedness first occurs in school-age children. There is some evidence that myopia is inherited. If one or both of your parents need glasses, there is an increased chance that you will too. Individuals who spend a lot of time reading, working or playing at a computer, or doing other close visual work may also be more likely to develop nearsightedness. Because the eye continues to grow during childhood, myopia typically progresses until about age 20. However, nearsightedness may also develop in adults due to visual stress or health conditions such as diabetes. A common sign of nearsightedness is difficulty seeing distant objects like a movie screen or the TV, or the whiteboard or chalkboard in school.
Eyeglasses or contact lenses can easily help with myopia. Depending on the amount of myopia, you may only need to wear glasses or contact lenses for certain activities, like watching a movie or driving a car. Or, if you are very nearsighted, they may need to be worn all the time.
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. This results in images being focused in back of the retina (Figure above). 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.
Common signs of farsightedness include difficulty in concentrating and maintaining a clear focus on close objects, eye strain, fatigue and headaches after close work, and aching or burning eyes, especially after intense concentration on close work.
In addition to lenses, many cases of myopia and hyperopia can be corrected with surgery. For example, a procedure called LASIK (Laser-Assisted in situ Keratomileusis) uses a laser to permanently change the shape of the cornea so light is correctly focused on the retina.
- 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.
Use the resources below to answer the questions that follow.
Explore More I
- Myopia, Hyperopia, and Astigmatism Explained at http://www.youtube.com/watch?v=6YxffFmi4Eo (1:55)
- How can the shape of your eyeball cause you to be farsighted? How does this affect your focal point?
- How can the shape of your eyeball cause you to be nearsighted? How does this affect your focal point?
- How can an irregularly formed cornea affect your vision?
Explore More II
- Nearsighted, Farsighted, and Reading Vision at http://www.youtube.com/watch?v=iws1Mfu1k84 (1:39)
- What is myopia? If you had this condition, when might you wear glasses?
- What is hyperopia? If you had this condition, when might you wear glasses?
- If you had an astigmatism, when might you wear glasses?
- At what age do many people start needing reading glasses? What causes this condition?
- Describe vision in people with myopia.
- What is hyperopia, and what type of lens corrects it?
- What causes myopia, and what type of lens corrects it?
- What are common signs of nearsightedness?
- What are common signs of farsightedness?