What is the difference between keratoconus and severe astigmatism?

Cone vs warp: Keratoconus is an abnormal conical shape of the cornea--sometimes severe enough that glasses cannot fully correct and surgery is considered. Astigmatism is more like a warp or bend in the surface of the cornea in a specific location. It is possible to have both at the same time. Talk to your Eye Dr if further questions.

Keratoconus is: progressive disease of the cornea in which the normally dome shaped cornea thins and begins to bulge into a cone-like shape. This condition needs to be monitored and possibly treated to prevent long term visual disability. Astigmatism is a refractive error, therefore it is not an eye disease it is an error in the focusing ability. Astigmatism is treated simply with glasses, contacts or surgery.

Abnormal vs. normal: KC is when the structure and strength of the cornea is abnormal, and the cornea becomes cone shaped. This causes IRREGULAR astigmatism (think of a lop-sided football). The steeper axis is greater on one side of the center than the other. Astigmatism, even severe form, is when the cornea is shaped like the surface of a football, steeper in one axis than the other, the same on both sides of center.