vision correction

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. This results in images being focused in back of the retina ( Figure 1.2). 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 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

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 1.1). In myopia, the eye is too long. Below, you can see how images are focused on the retina of someone with myopia ( Figure 1.2). 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 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. 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, oc- curs when objects are focused in back of the retina (bottom left). It is corrected with a convex lens (bottom right). 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.

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instructional diagrams

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questions

about 1 of every 2 people need some sort of vision correction.

-->  a. true

b. false

signs of myopia usually begin in childhood.

-->  a. true

b. false

an object is focused in front of the retina. this person has

a) myopia.

b) hyperopia.

c) nearsightedness.

-->  d) both a and c

an object is focused in back of the retina. this person has

a) myopia.

-->  b) hyperopia.

c) nearsightedness.

d) both a and c

common signs of myopia include

a) difficulty in maintaining a clear focus on close objects.

-->  b) difficulty is seeing the whiteboard at school.

c) headaches after close work.

d) all of the above

what is the main goal of corrective lenses?

a) the corrective lens changes the focus, so images move through the cornea.

b) the corrective lens changes the focus, so images moves through the eye lens.

c) the corrective lens changes the focus, so images move through the pupil.

-->  d) the corrective lens changes the focus, so images fall on the retina.

people with myopia will usually need glasses or contact lenses when they

a) work at a computer.

b) read a book.

-->  c) watch tv or drive a car.

d) all of the above

diagram questions

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