Explain with the help of ray diagram of convex lens to show the position of image and nature when object is placed :

Explain the eye defects in detail along with the method to correct them.

Explain the eye defects in detail along with the method to correct them.

● Myopia –

A person with myopia can see near by 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 front of the retina.

Causes of defect

● Excessive curvature of eye lens

● Elongation of eye-ball

Correction of defect

This defect can be corrected by using concave lens of suitable power. A concave lens of suitable power will bring the image back on the retina.

● Hypermetropia

In hypermetropia person Is able to see distant objects clearly but cannot see nearby objects distinctly. The near point for the person is farther away from the normal near point (25cms).

Cause of defect

● The focal length of eye is too long

● The eye ball has become too small

Correction of defect

This defect can be corrected by using a convex lens of appropriate power.

● Presbyopia

The power of accommodation of eye usually decreases with aging. For most of the people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distant objects also. This defect can be corrected using Bifocal Lens.

● Astigmatism

It takes place due to irregular curvature or spherical shape of the cornea. In this defect, person is not able to differentiate between vertical and horizontal lines at a time. It can be corrected using the cylindrical lens.

● Cataract

With ageing, the transparency and elasticity of lens gradually decrease. The crystalline lens of people of old age becomes milky and cloudy. Due to this reason, it starts reflection and objects seems cloudy. This condition is called Cataract. This can be corrected using minor surgical operation.