Just imagine what life was like for millions of people before glasses were invented. If you were short-sighted at that time, you were not able to see the clouds, distant mountains or birds flying through the air. Today, short-sighted people can see just like people with normal vision, thanks to glasses which improve their vision….Let’s start with a very simple example: We see because the light enters our eyes and falls on the retina, which is as sensitive as a photographic film of a camera. It is obvious that if the light falls behind or in front of the retina, we will not be able to see. Thus, there is a lens in the eye that refracts light so that it falls in the right place.
When the normal eye looks at distant objects, images always falls on the retina. But, when the same eye looks at an object that is close to it, within a distance of 5.5 meters, the image falls behind the retina. Therefore, the lens of the eye adjusts, and that means that one particular muscle shrinks and changes the shape of the lens, i.e its saliency. Because of that, the image again falls on the retina and the eye clearly sees the object.
There are two things that can disable this adjustment. Firstly, when people get older, the lens in the eye loses elasticity. They can no longer change their shape in order to correct the image created. Secondly, some people are born with too short or too long eyeballs. People whose eyeballs are too short are far-sighted. They can see distant objects, but their lenses have to be very adapt to be able to see objects close to them. Sometimes the lens cannot adjust enough to create an image on the retina. Beacuse of that these people have to wear glasses. Eyeglasses perform what their eye lenses cannot. Through the glasses, an image is created on the retina and the lens of the eye does not even have to adapt.
Short-sighted people have too long eyeballs. The image is created in front of the retina and looks blurred – and there is nothing a short-sighted person can do about it. If cramping a muscle can adapt the lens, it will only move the picture even further ahead. Thus, such a person wears glasses that move the image creation back to the retina, which allows a clear vision.
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Taken from: www.kako.hr