Biology, asked by aryaparashar2582, 10 months ago

Defects of vision and their correction

Answers

Answered by ranisrinivas1974
1

Three common refractive defects of the eye:

Myopia or Near-sightedness

Hypermetropia or Farsightedness

Presbyopia

Myopia

Near-sightedness : A person with Myopia can see nearby objects clearly

A person with myopia cannot see faraway objects clearly.

The far point for the myopic eye is nearer than infinity

Occurs due to

Excessive curvature of the eye lens

Elongation of eyeball

The image of a distance object is formed in front of the retina and not on the retina

Defected is corrected by using Concave lenses such that the lens will bring the image back on to the retina.

Hypermetropia

Far sightedness : A person with Hypermetropia can see faraway objects clearly.

A person with Hypermetropia cannot see nearby objects clearly.

The near point of the eye is more than 25cm

This arises mostly during latter stages in life, as a result of the weakening of the ciliary muscles and/or the decreased flexibility of the lens.

Focal length of the eye lens is too long

Eyeball has become too small.

The image of a distance object is formed in behind the retina and not on the retina

Defected is corrected by using Convex lenses such that the lens will bring the image back on to the retina.

Presbyopia

The power of accommodation of the eye usually decreases with ageing. The ciliary muscles weaken and thereby the flexibility of the eye lens reduces.

The near point moves away.

Spectacles with convex lenses are recommended

Myopia and Hypermetropia

Sometimes a person may suffer from both near sightedness and far-sightedness.

Such people are advised to use bifocal lenses.

Bifocal lenses consists of concave on the upper portion and convex on the lower portion.

Concave supports distinct vision and convex supports near vision

Refractive eye defects can also be corrected using contact lenses or through specific surgical procedures.

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