Question

defects of vision and its correction​

Answer 1

Hey mate ☺

There are mainly three types of defects of vision.

These are myopia, or near-sightedness, hypermetropia or far sightedness, and presbyopia.

MYOPIA :

In this defect the person is able to see nearby objects clearly but cannot see distant objects distinctly. A person with this defect has the far point nearer than infinity. In a myopic eye, the image of a distant object is formed in the front of the retina and not on the retina itself.

This defect may arise due to

(a) excessive curvature of the eye lens,

(b) elongation of the eyeball.

This defect can be corrected by using a concave lens of suitable power.

HYPERMETROPIA :

In this defect person is able to see distant objects clearly but cannot see nearby objects distinctly. The near point for the person is farther from normal near point (25cm). The image formed is behind retina in this defect.

This defect may arise due to:

(a) the focal length of the eye lens is too long

(b) the eyeball has become too small.

This defect can be corrected by using a convex lens.

PRESBYOPIA :

The power of accomodation 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.

This defect arises due to:

(a) the gradual weakening of the ciliary muscles ,

(b) diminishing flexibility of the eye lens.

Sometimes the person may suffer from both Myopia and Hypermetropia.

Such people boften require bi-focal lenses. A common type of bi-focal lenses consists of both concave and convex lens. The upper portion consists of a concave lens ,it facilitates distant vision and the lower part is a convex lens, it facilitates near vision.

Hope it helps you ☺✌✌

Answer 2

Answer:

Defects of the eye: Myopia: (nearsightedness) This is a defect of vision in which far objects appear blurred but near objects are seen clearly. ... This occurs when the eyeball is too short or the refractive power of the lens is too weak. Hyperopia can be corrected by wearing glasses/contacts that contain convex lenses.