Question

The change in focal length of an eye lens is caused by the action of the
(a) pupil.
(b) retina.
(c) ciliary muscles.
(d) iris.

Answer 1

Hey....!! HERE IS YOUR ANSWER....!!

CILIARY MUSCLE.....

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Answer 2

The change in focal length of an eye lens is caused by the action of the ciliary muscles, so the answer to this question is option c.  

The contraction or relaxation of these ciliary muscles alters the curvature of human eye lends.

The alteration in the curvature of eye lens modifying the focal length of eyes.  

Therefore, the change in the local length of eyes is created by ciliary muscles.