Astigmatism

Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. The lens and cornea of an eye without astigmatism are nearly spherical, with only a single radius of curvature, and any refractive errors present can be corrected with simple glasses. In an eye with astigmatism, either the lens or the cornea is slightly egg-shaped, with higher curvature in one direction than the other, giving distorted or blurred vision at any distance and requiring corrective lenses that apply different optical powers at different rotational angles. Astigmatism can lead to symptoms including eyestrain, headaches and trouble driving at night. It is often present at birth but can change or develop later in life, so it can affect people of all ages, and if it occurs in early life and is left untreated it may result in amblyopia.