Question

Why we myopia ,hypermetropia , presbyopia

Answer 1

Explanation:

Myopia:

• It is a defect in which the person cannot see distant objects clearly.
• This defect is happens due to increase in curvature of the eye lens or decrease in focal length of the eyes lens or elongation of the eyeball.
• In this defect the image of distant objects form behind the retina
• This defect can be corrected by using spectacles made of diverging or concave lens of suitable power.

Hypermetropia;

• In this defect a person is not able to see the nearby objects clearly

• This defect is due to the decrease in curvature of the eye lens or increase in focal length or the eyeball is becomes too small.
• In this defect the light rays from the nearby objects are focussed at a point behind the retina.
• This defect can be corrected using a converging lens or convex lens of suitable power.

Presbyoia:

• The power of accommodation usually decreases with ageing.This is also called old sightedness.
• The person with this defect cannot see nearby objects comfortably.
• This usually occurs due to ageing in people
• The ciliary muscles lose elasticity and cannot help in changing focal length of the eye lens properly.

Note: If a person suffers from both Myopia and hypermetropia then ,in this case Bifocal lens are used.