the working structure of eye
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When light enter into the eye it passes through pupil. Iris controls the amount of the light. The cilliary muscles help the lens to focus the object on the retina. When light strikes on either on the rods or the cones of the retina, it is converted into an electric signal. The photoreceptors in the retina convert the light into the electrical signals. These signals carried to the brain by optic nerves and nerve fibers. The brain then translates the electrical signal into images we see.
Each eye has own optic nerve and nerve fibers. Both optic nerves meet at the optic chiasm. From the optic chiasm, half of the optic nerve from each side cross to the other side and run (continue) to the backside of the brain.
Thus the right side of the brain receives impulses from the left optic nerve as well as right optic nerve and the left side of the brain receives impulse from the right optic nerve as well as the left optic nerve. Then the brain integrates the information to produce a complete picture....
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Answer ,: Eyes are spherical structures that consist of three layers.
(a) The outer layer is composed of sclera and cornea.
(i) Sclera is an opaque tissue that is usually known as white of the eye. It is composed of a dense connective tissue.
(ii) Cornea is a transparent anterior portion of 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 lens.
(b) The middle layer of eye is vascular in nature and contains choroid, ciliary body, and iris.
(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 posterior region and gets thickened in the anterior portion to form ciliary body. It contains blood vessels, ciliary muscles, and ciliary processes.
(iii) Iris: At the junction of sclera and cornea, the ciliary body continues forward to form thin coloured partition called iris. It is the visible coloured portion of eye.
The eye contains a transparent, biconvex, and elastic structure just behind the iris. It is known as 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. 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 with the brain.