The human eye is very much like the lens and screen you used in lab. When you look at an object the rays of light from the object are refracted through the lens cortex of the eye and an image is formed on the retina (screen) at the back of the eye. But for many people the image that is formed may not be clear. For nearsighted (myopic) people the image forms in front of the retina. For farsighted (hyperopic) people the image forms behind the retina. Fortunately there are many ways to correct vision problems so images form correctly on the retina. Essentially all methods involve changing the focal length of the eye by either adding another lens (eyeglasses or contact lenses) or directly changing the lens’s focal length through techniques like laser surgery.
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