Question

defects of vision and their correction class 10 don't spam

Answer 1

There are mainly three types of defects of vision:-

1. Myopia :- It is also known as near sightedness. A person with myopia can see nearby objects clearly but cannot see distant object.

Causes:- The defect may arises due to
i) excessive curvature of eye lens.
ii) elongation of the eyeball.

Correction:- This defect can be corrected by using concave lens of suitable power.

2. Hypermetropia:- It is also known as far - sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

Causes:- This defect may arises due to:-
i) the focal length of eye lens is too long.
ii) eyeballs becomes too small.

Correction:- This defect can be corrected by using convex lens.

3. Presbyopia :- The power of accommodation of the eye usually decreases with aging. For most people, near point gradually recedes away. They find it difficult to see nearby objects comfortably and distant objects clearly.

Causes:-
i) Due to gradual weakening of cilliary muscles.
ii) Diminishing flexibility of eye lens.

Correction:- This defect can be corrected by using bifocal lens. A bifocal lens consist both concave and convex lens. The upper portion consists of concave lens and the lower portion consists of convex lens.


Hope it helps.

Answer 2

DEFECTS OF VISION AND THEIR CORRECTION _______________

The defects due to which the person cannot see the object distinctly and comfortably are called defects of vision.

The main defects of vision are :
1. Myopia or near/short sightedness
2. Hypermetropia or far sightedness.
3. Presbyopia
4. Astigmatism
5. Colour blindness.

MYOPIA
In this defect , a person can see nearby objects clearly but cannot see distant objects clearly.
In this case image forms before retina not on the retina.
Remedy : This defect can be corrected by using concave lens of appropriate power. A concave lens of sweetable power will bring the image back on the retina, by diverging light rays initially thus the defect is corrected.


HYPERMETROPIA
In this defect a person can see distant objects clearly but cannot see nearby objects clearly.
A person with this defect has the near point farther away from normal near point (25 cm).
In this case the image forms beyond retina.

Remedy: This defect can be corrected by using convex lens of appropriate power. A convex lens of sweetable power will bring the image back on retina by converging light rays initially , thus the defect is corrected.




PRESBYOPIA
It is found in old age people. In this defect one cannot read comfortably and clearly. For most old age people, the near point gradually recedes away. Sometimes, a person may suffer from both myopia and hypermetropia.

Remedy: This defect can be corrected by using bifocal or varifocal lenses . The upper portion consists of a concave lens and lower portion consists of convex lens.



ASTIGMATISM
In this defect eye cannot focus both in horizontal and vertical lines clearly.

Remedy: This defect can be corrected by using cylindrical lenses or refractive surgery.



COLOUR BLINDNESS
In this defect the person cannot distinguish between certain colours. In such case if person is said to be colour blind .

Remedy: Because this defect is genetic , so it is not curable.



CATARACT
It is a condition in which crystalline lens of eye becomes milky and cloudy due to the growth of membrane over it. It generally occurs among people at old age. This causes partial or complete loss of vision. It is possible to restore vision through a cataract surgery.



I hope it helps you my dear friend.