Question

The change in focal length of an eye lens in human eye is caused by the action of the:
A. Pupil
B. Retina
C. Ciliary muscles
D. Iris

Answer 1

Hint: In this question, we need to comment on the muscle behind the change in focal length of an eye lens in the human eye. When the ciliary muscle tightens or relaxes, the curvature of the eye lens changes. The focal length of the eye lens is connected with the focal length of the eye.

Complete answer:
The ciliary is a circular muscle. The muscle relaxes or tightens the zonules to enable the eye lens to change its shape for focusing.The zonules are the fibres responsible for holding the eye lens suspended in position and also enable it to change the shape during accommodation.It is responsible for increasing or decreasing the focal length of the eye lens.
As the contraction and relaxation of the ciliary muscles change the curvature of the eye lens, this allows the eye lens to adjust according to the focal length of the human eye.
Therefore, on the basis of the above information, we can conclude that the change in focal length of an eye lens in the human eye is caused by the action of the ciliary muscles.

So, the option C is the correct answer.

Note:When we say the focal length of the eye changes, it means that the curvature of the eye lens gets charged. This happens only because of the tightening and the loosening of the eye lens. When the muscle gets relaxed, the lens becomes thinner. Similarly, when the muscle gets tightened, the lens becomes thicker. All this happens because of the actions of the ciliary muscles.The focal length of a human eye is approximately 22 millimetres.