Higher degrees of astigmatism are found after intraocular lens implantation than after routine cataract surgery. The cause is optical and is associated with the effectivity of lenses. The same amount of corneal astigmatism requires, in the spectacle correction, a cylinder that is smaller than, equal to, or larger than the corneal astigmatism, depending on whether the spherical equivalent of the refraction is a plus, zero, or minus sphere.