Little bit about human eye
Eyes focus light from surrounding and make an image and your brain understand this image and tell you what it is. They are like living cameras. Your eyes give you a three-dimensional colored picture of outside world. You recognize things by their color and shape and brightness.
Eyes have a clear window on the front which is called cornea. Tears help to keep eyes clean and moist which come from tear gland. Eyelashes and eyelids are to protect them, they make sure that any harmful particle cannot be reached to them.
Lens can be found on the back of cornea, they focus the light on a light sensitive layer of cells which is present on the back of the eye. This layer of cells is known as retina. Cells detect the image focused on the retina. The cell then send the message of image to brain through nerves. Brain take to mean of the massage and tells you what is it you are seeing. Eyes also have a patch which is known as yellow spot which can be found on the retina opposite to lens. This is the part of eye which is more responsive to colors.
Iris is a muscle sheet; it is present just behind the lens. This part is colored and has a round hole in the center which is known as pupil. In case you are in bright light, iris muscles contract and the pupil gets small, this way your eyes remain protected from intense light, which is harmful for them. On the other hand in dim light pupil stay relaxed and let the proper light enter so that you ca judge the image even in dull light or some time in dark too.
Humans have two eyes because if they had only one, to judge the depth and distance would have been almost impossible. The image which formed on the back of the eye would ne upside down but the brain will tell the right way of the image.
Millions of people have eyesight problems. To solve that some wear contact lenses and some wear eyeglasses to correct their vision. Many people are short sighted and many are long sighted, it is a job of optician to tell the exact problem and suggest the right lenses or contacts to those people. Eyeglasses were made in 13th century in Europe and china but they got famous in 15th century.
There are many other diseases related to eyesight. There are many people who are color blind; the only color they will see of every image will be white or black. Some people cannot judge the red and green color. And there are also people who are completely blind, it can be a childhood issue, they can be like that from the time they born or because of any unfortunate accident afterwards.
