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| Eye and vision |
As we read through this book, we saw a lot of written text, and pictures, we were able to see the images and read the text with our eyes. The old saying ‘seeing is believing’ quite appropriately defines the importance and necessity of sight. Sight or vision is possible because of our eyes, which are located in two sockets in front of our skull. The eyeball measures about 1 inch across and has muscles at the back which allow it to move upwords, downwords or sideways in both directions.
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Outer protection to the eye is provided by thin piece of skin called the eyelid and the hair at the end of the eyelids, called eyelashes. When we sleep the eye lids get closed thus covering the eyes and cutting off vision. Tear glands located just above the eyes produce moisture and as we blink our eyes, the eyelids clean the eyeballs with the help of this moisture. The eyeball is padded with a layer of fat and on the front it has a hole called the Pupil, this is surrounded by the Iris, which makes the pupil smaller or bigger depending upon the light outside. located on the front of the eyeball is the ‘Cornea’ which is like a transparent window, allowing partially focused light rays to enter the eye. Behind the cornea is a lens which focuses the light so that a fully focused but inverted image is formed on the ‘Retina’.
Located at the back, the retina is made up of a large number of rods and cones. The cones are sensitive to different colours while the rods are sensitive to black and whit, these rods and cones produce nerve signals when light reaches them through the Cornea. The inside of the eye is filled with vitreous fluid and Choroid which contains blood vessels for nourishing the eye. The retina is connected at the back to an optic nerve which inverts the image, right side up, while conveying the signals to the brain. The eye work togather duly controlled by the brain thus allowing us ‘binocular vision’.
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Medical