Question

The function of the ciliary muscle is
(a)To contract a pupil when one move in sunlight
(b)To keep the eyeball in position
(c)To rotate eyeball
(d)To change the shape of the lens

Answer 1

Hint: The ciliary muscle is an intrinsic muscle lying in the middle layer of the eyeball. It is also responsible for the production of a transparent, serous fluid known as the Aqueous humor.

Complete answer:
The function of the ciliary muscle is to change the shape of the lens.
->Ciliary muscle lies between the anterior border of the choroid and iris. It is composed of smooth muscle fibers oriented in three different directions; longitudinal, radial, and circular. It extends into zonular fibers that hold the lens.
->It helps in changing the focal length of the eyes by changing the radius of the curvature of the eye lens. This is known as accommodation.
->When the eye is focused on a distant object, the ciliary muscles are relaxed so that the focal length of the lens is increased. The parallel rays coming into the eyes are then focused on the retina.
->When the eye is placed on a closer object, the ciliary muscles are strained and the focal lens of the eyes lens decreases in such a way that the image is formed on the retina.
->The ciliary muscle can be divided into 'Pars plicata' (ciliary process) and 'Pars plana'.
->The aqueous humor produced by the ciliary processes first goes to the posterior chamber and then traverses to the anterior chamber of the eye.

So, the correct answer is ‘To change the shape of the lens'.

Note: The intrinsic muscles of the eye are muscles that control the movements of the lens and pupil and thus participate in the accommodation of vision. They are ciliary, dilator pupillae, and sphincter pupillae muscles. The sphincter pupillae causes the constriction of the pupil whereas the dilator pupillae dilates the pupil.