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. This gives distorted or blurred vision at any distance and requires corrective lenses that apply different optical powers at different rotational angles. Astigmatism can lead to symptoms that include eyestrain, headaches, and trouble driving at night. Often it is present at birth, but it can change or develop later in life, and so can affect people of all ages. If it occurs in early life and is left untreated, it may result in amblyopia. The cause of astigmatism is unclear, although it is believed to be partly genetic. The underlying mechanism involves an irregular curvature of the cornea and protective reaction changes in the lens of the eye, called lens astigmatism, that has the same mechanism as spasm of accommodation. Diagnosis is both objective (by an eye examination called autorefractor keratometry, which allows examination of the lenticular and corneal components of astigmatism) and subjective (by refraction). Three treatment options are available: eyeglasses, contact lenses, and surgery. Glasses are the simplest. Contact lenses can provide a wider field of vision and fewer artifacts than even double aspheric eyeglass lenses. Refractive surgery aims to permanently change the shape of the eye and thereby cure astigmatism. In Europe and Asia, astigmatism affects between 30% and 60% of adults. It was first reported by Thomas Young in 1801.