This is a common condition which is caused by an irregularity in the shape of the eye surface (cornea or lens) i.e. the eye surface is shaped more like a rugby ball than a football. This means that light passing through different regions of the cornea or lens is refracted or bent to different points of focus. Part of the image falling on the retina is blurred whilst another part will be in focus.
This is corrected with a TORIC / CYLINDRICAL lens.