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Human Body
1. SIGHT AND THE EYE The eye is a special organ of the sense of sight. Man depends on sight more than upon any other sense to supply information about his environment. The mobility of his eyes and head and stereoscopic? vision give him a panoramic view of the world i.e. information on depth, distance, dimension and movement. Eye's sensitivity to colours and contours enables him to distinguish between different colours and shades of colours. In addition, eyes can be extremely expressive of moods and emotions. Structure of the Eye
The Eyeball is situated in the orbital cavity. It has a highly complex structure. It is almost spherical in shape and is approximately 2.5 cm. in diameter. The bony walls of the cavity and the fatty cushion help to protect the eye from injury. Further protection is provided by eyelids, eyelashes and eyebrows.
Structurally, the two eyes are the same but some of their activities are coordinated so that they function as a
pair.
The anterior one-sixth of the eyeball is covered with a transparent layer called cornea, while the posterior fivesixths is covered by a tough fibrous layer called sclera. The Cornea, the bulge at the front is a window that lets light rays into the eye and bends or refracts them. A flat circular coloured membrane, the iris, lies behind the cornea and gives the eyes their characteristic colours. Between the cornea and the iris is a small compartment containing a clear fluid, the acqueous humour, which nourishes the cornea.
Tbe iris governs the size of the pupil, a small adjustable hole in its centre that regulates the amount of light entering the eye. The crystalline leps, lying behind the pupil, further refracts the light to focus a sharp image on the retipa, the inner layer of the wall of the cyeball. This thin screen, containing specialized photo-receptor cells, transforms light energy into electrical messages that are transmitted to the brain by the optic nerve which runs from the back of the eye. A large compartment, containing a 1. Vision from the two slightly different angles of the eyes,
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