Correcting Vision

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Farsightedness. If the eyeball is too short or the lens too flat or inflexible, the light rays entering the eye from nearby objects, will not be brought to a focus by the time they strike the retina. Glasses with convex lenses can correct the problem. Farsightedness is called hypermetropia.

Nearsightedness. If the eyeball is too long or the lens too circular, the image of distant objects is brought to a focus in front of the retina and is out of focus again before the light strikes the retina. Nearby objects can be seen more easily. Glasses with concave lenses correct this problem by diverging the light rays before they enter the eye. Nearsightedness is called myopia.