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The Human Body:
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Eye Surface
The eyeball has 3 major layers of protective covering. They are the sclera, choroids and retina.
The sclera is the tough outer layer, the whites of the eye which is the thickest of all the layers, about 1mm thick. At the front, it has a transparent curved part called the cornea which allow light to pass through.
The choroid, which is the 2nd underlying layer has millions of blood vessels which supply the retina with food and oxygen. This layer surrounds the eyeball except the front where the cornea is. The cornea is backed up with the iris and the pupil. The iris is the coloured part in the middle of the eye. The colour depends on the colour pigments present in the iris. The pigment, melanin, affects the colour of the eye and is inheritable from parents. The pupil is a hole inside which looks like a black dot. It opens and closes to allow the light to pass through.
The retina is the innermost layer which helps sight. It has millions of nerve cells called rods and cones which responses to light. These are attached to nerve fibers which joins to the optic nerve which links the eye to the brain, thereby allowing one to decipher and understand what is being seen.
At the point where the optic nerve leaves the eye, there are no rod and cones and is known as the blind spot.
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