Name the three layers of the eye wall and describe the functions of each layer.

The eyes are the sensory organ, gathering visible information from the surrounding and then transforming them into nerve impulse. They have a round appearance, with prominent bulge in the front region. The eye wall is the outermost part of the eye surrounding the jelly-like fluid ball.

The eyeball is enclosed in a three-layered wall, where each layer has a certain structural composition and a certain function.

The three layers of eye wall are:

1. Fibrous tunic or outer layer:  It is composed of dense connective tissue, and has two parts: sclera and cornea. Sclera encloses the whole surface of the eyeball and provide the points for attachment of muscles involved in regulating eye movement. Cornea allows the entry of light rays and then there bending, thus helping in focusing the light rays. Conjunctiva layer prevent the eyes from drying out by lubricating them with the tears.
2. Vascular tunic or middle layer: This layer of tissue includes the choroid, ciliary body and iris. Choroid is in the posterior 5/6 of the eye. It is composed of blood vessels, and thus supply nutrients and oxygen to the eyes. The anterior part of choroid progresses into the ciliary body, which holds the lens at its place, aid in adjusting the sight for near and far objects, producing, secreting and releasing the aqueous humor. The iris is present on the top of the lens. Iris governs the pupil size, and thus regulate the amount of light entering the eye.
3. Retina or inner layer: It is the light sensitive layer, composed of the photoreceptor cells and nerve cells. They help in forming the image of the perceived light.