Question

If the circular ciliary muscles of the eye are unable to contract, the
A. Lens will become more convex
B. Lens will be thin and stretched
C. Vision will be lost completely
D. Bright light will have no adverse effect on the retina

Answer 1

Hint: The ciliary muscle is termed as the intrinsic muscle that occurs in the middle layer of the eyeball. It is also required for the production of a transparent, serous fluid known as the aqueous humour. Ciliary muscles help to protect the iris.

Complete answer: The major role of the ciliary muscle is to change the shape of the lens. The ciliary muscle is present between the anterior border of the choroid and iris. It is made up of smooth muscle fibres and is directed in three different directions; longitudinal, radial and circular. It extends into zonular fibres that hold the lens. It plays a major role in changing the focal length of the eyes by changing the radius of the curvature of the eye lens. It is also termed as accommodation. When the eye is focused on an object that is at a large distance, the ciliary muscles are relaxed so that the focal length of the lens is increased. The parallel rays generating into the eyes are then focused on the retina. When the eye is shown 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 developed on the retina. The ciliary muscle can be categorised into 'pars plicata' (ciliary process) and 'pars plana'. The aqueous humour that is generated by the ciliary processes first goes into the posterior chamber and then traverses to the anterior chamber of the eye.
Hence, option B is the correct answer.

Note: The intrinsic muscles of the eye helps to control the movement of the lens and pupil and thus, take part in the accommodation of vision. They are termed as ciliary, dilator pupillae, and sphincter pupillae muscles. The sphincter pupillae leads to the constriction of the pupil, whereas the dilator pupillae dilates the pupil.