what causes short-sightedness? is it the shape of eyeball or the lens?

Answers:
Myopia = short-sightednesscornea is too curved or the EYEBALL too long

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shape of the eye ball.

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eyeball is elongated so the focal point of the eye is before the retina. Commonly called short sightedness or myopia in it's medical term.http://en.wikipedia.org/wiki/myopia.

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Short-sightedness is caused by a change in the shape of the eyeball.

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Short sightedness, doesn't have to do with the EYE at all.Short-sighedness, has to do with the MIND. and your attitude.Near-sightedness. on the other hand. can be a little of both.

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The shape of the eyeball is too long, meaning the distance from the lens to the retina is too long.

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Far sighted and near sighted is caused by the shape of the eyeball. Short sightedness is caused by education or environment.

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It can be caused by defects in either of them as follows:
1-the eyeball could be elongated,so that the focal point (point where the light rays entering the eye collect together) becomes in front of the retina..or:
2-the eye lens is very powerful (more biconvex than normal) so that it collects the light rays b4 reaching the retina.!!
cya!

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It is caused by the eye lens being too powerful because its curvature cannot be sufficiently reduced, in turn causing rays from a distant object to be focused in front of the retina instead of on it.

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It is the shape of the eyeball. If you watch tv too close or read under dim light, the eye balls for some reason just become longer. That would worsent the myopia.

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Short-sightedness or "near-sightedness" can be caused by two different factors. One is the shape of the eyeball being too long, and the other isn't the lens, but rather the cornea (which covers the lens) being too "thick" or sticking out too far from the eyeball. Both of these cause objects further away to focus in front of the retina in the eye.

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%26gt;if it's the eyeball, why are we not advised to watch tv too close, or read under dim light?There is good evidence that too much "close work" makes it more likely for those succesptible to myopia to become myopic. The best evidence endicates that it's a complex interaction between genes and environment. Once you reach adulthood, though, and your eye stops growing, I don't think it's nearly so likely to change shape.

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Short-sightedness is also known as myopia.A person can see nearby objects clearly but cannot see the distant objects so distinctly.This defect arises due to the following reasons:
(i) excessive curvature of the cornea,or
(ii) elongation of the eyeball.
This defect can be corrected by using a concave(diverging)lens.

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