Astigmatism can be corrected by using
Convex lens
Concave lens
Cylindrical lenses
Both a and b
As we have discussed in Disorders of Eye:
Astigmatism: This abnormality of vision is due to the irregularities in the shape of the lens and cornea. The lens shows different curvatures in different regions of the eye. So the light rays are not brought into sharp focus on the retina. This defect is corrected by the cylindrical lens.
Hence, Cylindrical lenses is the correct option.