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Eye conditions such as near- or far-sightedness are often mechanically corrected by glasses or contact lenses. They both work roughly the same way; the lens affect the movement of the light entering their front, and cause it to swerve out of its direct path to hit the proper sections of the eyeball. These lenses are called divergent or convergent lenses. This means that they cause the light waves to diverge (split apart) or converge (focus together). A convergent lens focuses the light together, allowing a far-sighted person (who would normally have good distance vision and worse close vision) to see things up close without blurriness. Far-sightedness is called hyperopia. Convergent lenses are thicker in the center and thinner at the sides, allowing the proper focusing of light, similar to a common magnifying glass but specifically ground for a person's unique vision issues. Patients with astigmatism sometimes have lenses that are ground with both convergent and divergent surfaces, so as to focus the light on the areas of their eyes where the focal distance is different.
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