NEAR SIGHTEDNESS
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In a near sighted eye, incoming light rays form an image in front of the retina because the cornea is curved too strongly or the eyeball is too long.
Result: objects at a distance appear blurred and out of focus.
FAR SIGHTEDNESS
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In a far sighted eye, images form behind the retina ,because the cornea is curved too weakly or the eyeball is too short .
Result: close objects appear blurred.
ASTIGMATISM
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In an astigmatic eye, the cornea has an uneven curvature. Instead of converging at one focal point ,light rays merge in a line infront of or behind the retina. Astigmatism can also occur in combination with near-sightedness and far sightedness.
Result: a distorted view of objects.