Explain structure of human eye?
Answers
Human Eye:
- Human eye is a sensitive sense organ .
- It acts like a camera, enable us to capture the colourful picture of the surroundings.
- It forms an inverted, real image on light sensitive surface Retina.
The Various parts of eye and their functions:
Cornea:
- It is the transparent spherical membrane covering the front of the eye light enters the eye through this membrane.
Crystalline lens:
- The eye lens is a convex lens made a transparent, soft and flexible material like a jelly made of proteins.
Iris:
- It is a dark muscular diaphragm between the cornea and the lens. It controls the size of pupil.
Pupil:
- It is a small hole between the iris through which lights enters the eye.
- In dim light, it opens completely due to expansion of iris muscles.
- But in bright light it becomes very small due to contraction of iris muscles.
Ciliary muscles:
- They hold the crystalline lens in position and helps in modifying the curvature of the lens.
Retina:
- It is light sensitive surface of the eye on which the image is formed.
Optic Nerve:
- It transmit visual information from the retina to the brain.
Aqueous Humour:
- Between the cornea and eye lens, we have space filled with transparent liquid called aqueous humour.
- It helps the refracted light to be focused on retina.
Vitreous Humour:
- Space between eye lens and retina is filled with another liquid called vitreous humour.
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.
Explanation: