A Wonderful Gift Called Eyes
Have you ever tried to see the world around you with your eyes closed? Try. You will realize the significance of the walnut sized pair of eyes. Eyes are responsible for more than 90% of our communication with the outside world. No wonder they are marvellous piece of high tech sophisticated optical electronic organ.
Each eye is about 24mm in diameter, suspended by six muscles within the bony cavity called orbit of the skull. These dozen muscles (six each eye) work throughout our lives to move the eye in all directions and keep them aligned to the object we see. Slightest abnormality or weakness leads to squint or double vision. The bony orbit margin is strong and protects the eyes from injury from larger objects. Lids, upper and lower cover eyes. They work as wiper to keep the transparent front part of the eye clear.
Cornea is like the glass in front of a watch. It is the first tissue of the eye where light strikes and passes through to reach the photosensitive layer retina. Eleven millimetre in diameter and about 0.6 mm in thickness, cornea occupies 1/6 surface of the eyeball. It is ultimate model of transparency and is designed to reduce optical aberrations. It is also designed to absorb and filter ultraviolet light from reaching the retina. Since it is transparent, one can only see it with a special instrument known as slit lamp bio-microscope.
Through the cornea one can see the brown/blue part of the eye the Iris. It is akin to an aperture diaphragm of the camera. Equipped with rapidly acting tiny muscles, it controls the size of the dark central black part called the Pupil. The size of pupil is adjusted according to the available ambient light. You go out in sun and it contracts to cut off extra light. Go to a movie and it dilates to permit entry of more light.
Behind iris there is an auto-focusing Lens faster than fastest auto-focus camera. It is adjusted by billionth of a second to keep the world around you in sharp focus whether it is at 10 cm or at one kilometre.
The photosensitive layer of eye is called Retina. A spongy vascular layer called Choroid supplies nourishment to the retina and lines the outer surface of the retina. Behind the lens and in front of Retina is a cavity filled with clear jelly called Vitreous. Ten layered and 0.2 mm thick, the retina is the most complex and efficient part of the human body. Developmentally it is the part of the brain. The cells once damaged cannot be repaired. It contains about 140 million photosensitive cells, which convert light to electrical current, a millionth of a volt, which is transmitted along wires in a bundle called Optic Nerve, to the brain. The photoelectric cells of the retina are known as rods or cones. Rods are concerned with peripheral and night vision and cones are present in the central sharp and colour vision. These cells gather all the information pertaining to vision and pass it on to the brain via Optic Nerve, which is made up of nerve fibres. The mind then interprets these signals into a three-dimensional full colour motion picture of our surroundings.
Eyes probable are the greatest creation of GOD.
-Dr. SPS Grewal
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