In this defect, a person cannot focus on both horizontal as well as vertical lines at the same time. So he can see the objects clearly only in one plane.This defect is mainly due to the cornea that is not perfectly spherical. As a result, the cornea has different curvatures in different directions of the horizontal and vertical planes. This defect can be corrected by using cylindrical lenses of suitable focal length and suitable axis in the spectacles.
