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Description of presbyopia and astigmatism

Give a brief description of presbyopia and astigmatism?

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Presbyopia is visual impairment in which there is loss of cililary muscle strength thus reducing the ability of crystalline lens to adjust images of near objects on retina. In presbyopia the near point of vision becomes more distant. The disease generally takes place in old people.

Astigmatism is caused by the irregular shape of refractive structures, mainly cornea. In astigmatism a single object-point might create more than one image on retina and so the vision becomes distorted.

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