Human eye is spherical in shape. Any object with spherical shape has the ability to focus light rays. There are three most important parts inside the human eye that helps us see an object. They are retina, cornea and the pupil.
· Retina is a curved part that reacts to light and conveys information to the brain.
· Cornea is the bulging white surface in front of the eye.
· Pupil or iris is the black hole through which light passes.
There is a lens between retina and the pupil. This lens will focus the scattered light to the surface of retina and reduce the size of image to fit into the retina. Then retina sends the light signals to the brain which processes them and turns them into images.
When the image is not properly formed due to improper focusing by the lens or defective cornea/retina, defective vision happens. Defective vision has to be corrected by wearing glasses with suitable lens. Myopia or near-sightedness causes people to see closer objects clearly but farer ones appear blurred. In this case, a concave lens is used to correct the vision. Hyperopic condition or farsightedness causes farer objects to appear clearly whereas closer ones appear blurred. This defect is corrected using convex lens.
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