Hi Astigmatism is due to variable shape of the cornea. Sometimes high astigmatism can be associated with Keratoconus wherein the cornea becomes conical in shape causing visual distortions.

Both are corneal irregularities. Keratoconus is more severe to type of astigmatism

Both are the corneal irregularities Where keratoconus is the advanced version of astigmatism where the cornea gets de-shaped and needs urgent treatment

Astigmatism is irregularity in corneal curvature. It can be corrected with glasses. Keratoconus is severe irregularity in corneal curvature. This causes such irregularities in cornea that vision may not be corrected with glasses. Patient needs rigid contact lenses and/ or other modalities to improve vision. So ,I can say All astigmatism is not Keratoconus. But all Keratoconus patients have astigmatism.