Question

Write the function of the following part of the human eye.
Ciliary muscles.

Answer 1

The basic function of the muscles is to allow movement of the different organs. The other functions of the muscles include temperature regulation and vision control. This is where the function of ciliary muscles come into picture.

Complete answer:
The accommodation of vision is brought about by the pupils and the lens of the eye. The muscles that control the movement of these parts are the intrinsic muscles. The intrinsic muscles of the eye include the ciliary muscle, dilatator pupillae and the sphincter pupillae.
The ciliary muscles are the major part of the ciliary body which is an extension of the iris, the coloured part of the eye. It lies between the anterior border of the iris and choroid. The ciliary muscles are composed of the smooth muscles which are oriented in three directions namely radial, longitudinal and circular. The control of these muscles is brought about by the parasympathetic nerves.

Working of the muscles:
The contraction of the ciliary muscles increases the convexity of the lens and thus helps the eye to accommodate itself to see near objects (for near vision). The relaxing of the ciliary muscles causes the lens to become flat and reduces the focusing power and helps in far vision. The ciliary muscles are not directly attached to the lens, they are attached through fibres called zonular fibres.

There are three separate layers in the ciliary muscles namely longitudinal layer, middle layer and the circular layer. The circular layer is the innermost layer, the longitudinal layer is the outermost and the middlemost layer is the transition from outer to inner layer.

Note: The attachment of ciliary muscles is not exactly determined yet. Some authors say that the ciliary muscles originate from a protrusion of the sclera into the scleral spur. The scleral spur is an elevation seen in the anterior chamber made up of the trabecular tissue.