Question

what is defect of vision ?what are the main causes of it?
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Answer 1

Answer:

Defects of Vision. ... There are mainly three common refractive defects of vision. These are (i) myopia or near-sightedness, (ii) Hypermetropia or far – sightedness, and (iii) Presbyopia. These defects can be corrected by the use of suitable spherical lenses. We discuss below these defects and their correction

Explanation:

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Answer 2

$\Large\underline\mathfrak{Question}$

what is defect of vision ?what are the main causes of it?

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$\Large\bold\star\underline{\underline\textbf{Hypermetropia\:}}$

Defect

→ In this defect a person cannot see nearby objects clearly but distant objects are clearly visible.

Correction

→ This defect can be corrected by using

suitable convex lens. This defect is also called long sightedness.

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$\Large\bold\star\underline{\underline\textbf{Myopia\:}}$

Defect

→ In this defect a person cannot see distant objects clearly but nearby objects are clearly visible.

Correction

→ This defect can be corrected by using suitable concave lens. This defect is also called near sightedness.

Cause

→ Cause of Myopia: This defect arises due to either ,

1). elongation of the eye ball.

2). excessive curvature of the cornea.

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$\Large\bold\star\underline{\underline\textbf{Astigmatism\:}}$

Defect

→ In this defect a person cannot focus in both horizontal and vertical lines clearly.

Correction

→ This defect can be corrected by using cylindrical lenses. During this rays of light converge as lines instead of converging as points on the retina.

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$\Large\bold\star\underline{\underline\textbf{Presbyopia\:}}$

Defect

→ ) It this defect a person cannot see nearer as well as distant objects clearly.

Cause

→ It is due to weakening of the ciliary muscles and also elasticity of the eye lens decreases.

Correction

→ It can be corrected by bifocal lenses.

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Hope it helped u.

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