Solution

Eyes are photoreceptors which help in the sensation of vision.
(a) Sclera and cornea form the outer layer.
(i) The sclera is an opaque tissue that is usually known as white of the eye. It is composed of a dense connective tissue.
(ii) The cornea is a transparent anterior portion of the eye that lacks blood vessels and is nourished by lymph from the nearby area. It is slightly bulged forward and helps in focusing light rays with the help of the lens.
(b) Choroid, ciliary body, and iris constitute the middle layer.
(i) Choroid lies next to the sclera and contains numerous blood vessels that provide nutrients and oxygen to the retina and other tissues.
(ii) Ciliary body: The choroid layer is thin over the posterior region and gets thickened in the anterior portion to form the ciliary body. It contains blood vessels, ciliary muscles, and ciliary processes.
(iii) Iris: It regulates the size of muscles by the contraction and relaxation of iris muscle.
The eye contains a transparent, biconvex, and elastic structure just behind the iris. It is known as a lens. The lens is held in position by suspensory ligaments attached to the ciliary body. The lens divides the eye ball into two chambers – an anterior aqueous and posterior vitreous chamber.
(c) The innermost nervous coat of eye contains retina. The retina is the innermost layer. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types – rod cells and cone cells.
(a) Rod cells –The rods contain the rhodopsin pigment (visual purple) that is highly sensitive to dim light. It is responsible for twilight vision.
(b) Cone cells –The cones contain the iodopsin pigment (visual violet) and are highly sensitive to high-intensity light. They are responsible for daylight and colour visions.
The innermost ganglionic cells give rise to optic nerve fibre that forms optic nerve in each eye and is connected to the brain.