Vision Correction
Vision Correction
Introduction | Myopia | Hyperopia | Presbyopia | Astigmatism | Strabismus | Cataracts
Introduction
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Obtained from Encarta Encyclopedia 2004 |
The eye normally focuses the image on the retina. This is accomplishedby a convex lens inside the eye that can become wider or narrower tocondense the light. Sometimes, however, something inside the eye is notfunctioning correctly. This makes the vision blurry or disoriented insome other fashion. I am going to explain these disorders and howlenses correct them.
Below is how people with an eye disorder see the world.
Below is how people with an eye disorder see the world.
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Astigmatism Obtained from www. allaboutvision. com | Cataract Obtained from www.nei. nih.gov | Hyperopia Obtained from www. allaboutvision. com | Myopia Obtained from www. allaboutvision. com | Strabismus Obtained from www. allaboutvision. com |
Glasses are lenses inside a frame. Contact lenses are pieces of plastic or glass that rest on the eye, separated from the eye by a thin layer of tears.They are used to correct eye disorders. There are lots of kinds ofglasses, but the most common kinds treat myopia, hyperopia, presbyopia,and/or astigmatism.
Myopia
Myopiais more commonly known as nearsightedness. It is is when you cannot seeobjects at a distance, such as a street sign, but are fine whilelooking at near objects, such as a book, unless the myopia is verysevere. Nearsighted people might have headaches and eyestrain, and maysquint or feel tired while playing sports or driving. It runs infamilies and usually appears when they are a kid.
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Obtained from Encarta Encyclopedia 2004 |
If the eye has myopia, the eye is too long, and the image falls short of the retina when the target object is far away.
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Obtained from http://www.psych.ucalgary.ca |
Myopiamay be corrected with lenses. Concave lenses are used here. Theyspread the light out before it reaches the convex lens in the eye,therefore letting the image focus directly on the retina.
Hyperopia
Hyperopiais known to you probably as farsightedness. People with hyperopia willusually see far-away objects, such as the TV, crystal clear (unless thehyperopia is very severe), but cannot see close objects clearly (suchas needlework). Hyperopic people may feel the same things a nearsightedperson does, but in this case, they feel it at close range, not farrange.
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Obtained from Encarta Encyclopedia 2004 |
The eye is shorterthan normal in the case of hyperopia and the image focuses behind theretina if the target object is near. This means it doesn’t focus evenwhen it reaches the retina.
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Obtained from http://www.psych.ucalgary.ca |
Hyperopia can be corrected with a convex lens. Aconvex lens focuses the light in addition to the natural lens and makesthe image focus exactly on the retina. Many people have hyperopia as akid, but some of them lose is as the eyeball grows longer with normalgrowth.
Presbyopia
Presbyopiais part of aging. When someone gets into their forties, and is causedby the hardening of the crystalline lenses in the eye. People with thiswill find that their arms are “getting shorter” as they have to holdreading material farther and farther away.
Presbyopic people and hyperopic people have the same general view, buthyperopia is caused by a short eye, and presbyopia is caused by a hardlens. Presbyopia is also corrected with a convex lens. It is correctedusing the same principle as hyperopia.
Astigmatism
Astigmatism is the most common eye disorder. Astigmatism can accompanymyopia or hyperopia. Astigmatism can be barely noticeable in smallamounts. Most people don’t even aware it! However, some uncorrectedastigmatism give you eyestrain or headaches, and distort or blur visionat all distances.
Astigmatism is the result of anirregularly shaped cornea (the transparent part of the eye that coversthe rest of it) or lens. Astigmatism is when the cornea is shaped likea football instead of like a baseball. This makes the light rays focuson two spots instead of one on the retina because the cornea has a steeper and flatter curve than normal.
Astigmatism is the result of anirregularly shaped cornea (the transparent part of the eye that coversthe rest of it) or lens. Astigmatism is when the cornea is shaped likea football instead of like a baseball. This makes the light rays focuson two spots instead of one on the retina because the cornea has a steeper and flatter curve than normal.
The steeper and flatter curve can too be corrected with lenses. Acylindrical curve in the glasses lens compensates for the footballshape and makes it equivalent to the normal baseball-shaped curve. Bothsoft and hard contact lenses can be also used to correct astigmatism. In conjunction to the one for astigmatism, the lens may contain acorrection for myopia or hyperopia .
Strabismus
Strabismus,more commonly known as crossed-eyes, is when the two eyes do not looktoward the same object together. One eye is normal, while the other onepoints in some other direction. Strabismus can be corrected withprisms. The prisms bend the light so the light goes to the correct spot.
Cataracts
Acataract is when the lens of the eye or its capsule is opaque. It isthe leading cause of blindness in the world. The word “cataract” meanswaterfall. For someone with a serious cataract, it's like seeingthrough a waterfall to them.
Age-related cataracts develop in two ways. The fibers that make up thelenses in your eyes clump together to blur vision or the lens gets ayellowish/brownish tint. Symptoms of a cataract include cloudy orblurry vision, faded colors, excessive glare from light or a haloaround lights, bad night vision, double vision, or frequent glasses orcontact lens prescription changes.
Early cataracts can be treated with new glasses or magnifying lenses.If these do not work, surgery will have to be used. Cataract surgeryinvolves removing the natural lens inside the eye and replacing it withan artificial one.
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