Eyes Vision Defects

The four most common eye disorders, or refractive errors, are nearsightedness, farsightedness, presbyopia and astigmatism. They are not diseases, but simply minor defects in the construction of the eye. The human eyes get its adult size and shape when a person reaches his or her twenties. At that point, the disorders like nearsightedness, astigmatism, and farsightedness usually stabilize.

Nearsightedness is scientifically known as myopia which means that a person sees nearby objects more clearly than the distant objects. It does not mean that a myopic person has perfect or excellent near vision and poor distance vision. Extremely nearsighted people can not see anything clearly. In the normal eye, parallel rays of light passing through the cornea bend slightly and then bend again as they penetrate the lens to focus on a single, small spot on the retina; but in the nearsighted eye, a steeply curved cornea or an elongated eyeball, or both, focus rays of light before they reach the retina. From this focal point the rays of light begin to diverge. By the time light reaches the retina, and the image is blurred.



Farsightedness, scientifically known as hyperopia, is the opposite of myopia. It is not necessarily the ability to see objects clearly at a distance and poorly at close up, although this can be the case. In the farsighted eye, rays of light streaming through the lens and cornea reach the retina before they come into focus, creating a blurred image. In the sense, the eyeball is too short for the refractive power of its own optical system. Sometimes, mildly farsighted people do not discover this refractive disorder until middle age, when they begin to have trouble seeing clearly at close distances. This explains the common need for reading glasses among our middle-aged population.

Presbyopia is an optical flaw that eventually affects most of the people. As the eyes get older, their powers of accommodation decline. It becomes increasingly difficult for the eyes to properly bring nearby objects into focus. An individual with presbyopia can also be nearsighted, farsighted or astigmatic at the same time. If this is the case, bifocal glasses can give the eyes extra help with nearby objects, no matter what other refractive errors the eyes may have.



An astigmatic eye results from an imperfectly shaped cornea structure. The cornea of the astigmatic eye might be poorly curved from side to side or from top to bottom. This error of structure gives the cornea different refractory powers across its length and width and distorts sight. Some light rays focus in front of the retina and others just behind it. As a result, the retina never receives a sharp single image.



Most refractive vision errors may be corrected with contact lens or eyeglasses. A more permanent solution for many individuals exists today with a laser eye surgery procedure such as LASIK. In many cases a laser surgical procedure can eliminate the need completely for glasses or contacts. In any case, it is of extreme importance that any and all vision problems be thoroughly assessed by a qualified opthamologist who can advise the best course of eye treatment.

• John Palsson
• 15/11/2008, 7:42 PM
• 0 Comments