What are presbyopia and astigmatism?
Presbyopia is the visual impairment in which there is loss of the cililary muscle strength therefore reducing the capability of the crystalline lens to adjust images of near objects onto the retina. In presbyopia the near point of vision becomes more distant. The disease normally occurs in old people.
Astigmatism is caused by irregular shape of the refractive structures, mostly the cornea. In astigmatism a single object-point might produce more than one image onto the retina and so the vision becomes distorted.