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                                DEFECTS OF VISION

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                                DEFECTS OF VISION

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Eye defects are something that most people face nowadays. In some cases, the defects of eyes are present from the birth. Most of the defects are developed later in eyes.

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Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Such a person may see clearly upto distance of few metres.

Cause of Myopia and treatment
Causes
1) Excessive curvature of the eye lens
2) elongation of the eyeball

Treatment
This defect can be corrected by using a concave lens of suitable power. A concave lens of suitable power will bring the image back on to the retina and thus the defect is corrected.

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Hypermetropia is also known as far-sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.  Such a person has to keep a reading material much beyond 25 cm from the eye for comfortable reading.

Causes of Hypermetropia and treatment
Myopia is caused  because the light rays from a closeby object are focussed at a point behind the retina
Causes
1)  The focal length of the eye lens is too long
2)  The eyeball has become too small

Treatment
This defect can be corrected by using a convex lens of appropriate power. Eye-glasses with converging lenses provide the additional focussing power required for forming the image on the retina.

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The power of accommodation of the eye usually decreases with ageing. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia.

Causes of Presbyopia and treatment
Causes
1)  Gradual weakening of the ciliary muscles
2)  Diminishing flexibility of the eye lens

Treatment
Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bi-focal lenses.
A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision.