Question

List the 2 causes of presbyopia. draw labelled diagram of a lens used for the correction of this defect of vision.

Answer 1

Presbyopia= It is the defect of vision due to which an old person cannot see the nearby object clearly due to loss of accomodation of the eye..

Cause of presbyopia=

• Gradual weakening of ciliary muscle.

•Diminishing flexibility of eye lens.

Correction of presbyopia=

• Use of both concave and convex lens of suitable power.

•Such people require bifocal for correction.

•Sometimes a person may suffer from both myopia and hypermetropia..

...

I hope you understand

please mark as brainliest

Answer 2

Answer:

Presbyopia is special case of hypermetropia.we can call it old age hypermetropia.

In old age , due to weaking of ciliary muscles and eyes lens becomes inflexible [rigid] so the eyes looses its power of accommodation.

Because of this old person cannot see nearby objects clearly. 

Presbyopia is corrected using convex lens in spectacles.

it an also happen that a person with this defect cannot see far objects also.

So presbyopia has both defects myopia and hypermetropia.

Correction : A person is advised Bi - focal lens  spectacles in which upper part is concave and lower part is convex.