Astigmatism is a type of refractive error in which the eye does not focus light evenly on the retina.
In a camera, astigmatism refers to a defect caused by the inability of a single lens to focus oblique rays uniformly. In humans as in cameras, this results in distorted or blurred vision at any distance. For humans, however, other symptoms can include eyestrain, headaches, and trouble driving at night. If it occurs in early life, it can later result in amblyopia.
The cause of astigmatism is unclear, however, it is believed to be partly related to genetic factors. The underlying mechanism involves an irregular curvature of the cornea or abnormalities in the lens of the eye. The diagnosis is by an eye examination.
Three treatment options are available: glasses, contact lenses, and surgery. Glasses are the simplest. Contact lenses can provide a wider field of vision. Refractive surgery permanently changes the shape of the eye.
In Europe and Asia, astigmatism affects between 30 and 60% of adults. People of all ages can be affected by astigmatism. Astigmatism was first reported by Thomas Young in 1801.