Astigmatism

Astigmatism is a refractive error characterised by a variation in the dioptric power of the eye from one meridian to another.

The most common symptom is diminished visual acuity.

The aetiology is still unknown, but it is probably influenced by both genetic and environmental factors.

Among the common risk factors are a family history of astigmatism; myopia; Native American, East Asian, Hispanic, or Brazilian ethnic origin; eye trauma or surgery; and certain genetic and eyelid pathologies.

In most cases, the diagnosis is clinical and further diagnostic tests are usually not necessary.

Screening in the paediatric population is essential, primarily to decrease the risk of amblyopia.

Astigmatism is a refractive error characterised by a variation in the dioptric power of the eye from one meridian to another. Instead of having a spherical cross-section, the cornea and/or lens is cylindrical, with different focal power depending on the plane in which the light travels (the meridian). The meridians that have the greatest and the least dioptric power are known as the principal meridians. Astigmatism is termed regular when the principal meridians are at 90° to each other; otherwise, it is termed irregular. When astigmatism is present, the optical system is incapable of generating a clear image.[1]Benjamin WJ. Borish's clinical refraction, 1st ed. Philadelphia, PA: W.B. Saunders; 1998.