Question

State and explain the defects of vision. How can these defects be rectified ?

Answer 1

Defects of vision :

The defects of vision are;

i) myopia (or) nearsightedness.

ii)Hypermetropia (or) farsightedness.

iii) presbyopia.

a. Myopia (nearsightedness)

A person with myopia can see nearby objects clearly and cannot see distant objects distinctly.

Reason: i) Excessive curvature of the eye lens

ii) Elongation of eyeball

Rectification: Using a concave lens of suitable power

b. Hypermetropia (farsightedness)

A person with this defect can see the distant objects clearly but cannot see the nearby objects.

Reason : (1) The focal length of the eye lens becomes too long.

(2) Eyeball becomes too small

Rectification: By using a convex lens with suitable power

c. Presbyopia

The power of accommodation of the eye usually decreases with ageing. For most people, the near point gradually recedes they find it difficult to see nearby objects comfortable and distinctly.

Reason: Gradual weakening of ciliary muscles and diminishing flexibility of eye lens.

Rectification: Can be corrected with bifocal lenses.