Regular astigmatism - principal meridians are perpendicular.

Includes Myopia (positive defocus), hyperopia (negative defocus), and regular astigmatism.

(This is regular astigmatism, which is by far more common than irregular astigmatism where separations are other than 90 ).

The more common regular astigmatism arising from either the cornea or crystalline lens can be corrected by eyeglasses or toric lenses.

Low order aberrations (hyperopia, Myopia and regular astigmatism), are correctable by eyeglasses, soft contact lenses and refractive surgery.

The 2 steep hemimeridians, 180 apart in regular astigmatism, may be separated by less than 180 (a situation called nonorthogonal); and the 2 steep hemimeridians may be asymmetrically steep-that is, one may be significantly steeper than the other, as shown by a larger magnitude value.