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Define the terms astigmatism and presbyopia

Define the terms astigmatism and presbyopia?

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Presbyopia is the visual impairment in which there is a loss of cililary muscle strength therefore dropping the capability of crystalline lens to adjust images of close objects onto the retina. In presbyopia, the near point of vision becomes more far-away. The disease usually takes place in old people. Astigmatism is caused by the irregular shape of refractive structures, mostly the cornea. In astigmatism, a single object-point might generate more than one image onto the retina and therefore the vision becomes distorted.

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