In geometric optics, stigmatism refers to the image-formation property of an optical system which focuses a single point source in object space into a single point in image space. Two such points are called a stigmatic pair of the optical system. Many optical systems, even those exhibiting optical aberrations including astigmatism, have at least one stigmatic pair. Stigmatism is applicable only in the approximation provided by geometric optics. In reality, image formation is at best diffraction limited and point-like images are not possible.
Astigmatism is a type of refractive error in which the eye does not focus light evenly on the retina. This results in distorted or blurred vision at any distance. 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. 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.
Image-formation property of an optical system which focuses a single point source in object space into a single point in image space
Normal eyesight, anastigmatic state
State of having stigmata
A defect of a lens such that light rays coming from a point do not meet at a focal point so that the image is blurred.
A disorder of the vision, usually due to a misshapen cornea, such that light does not focus correctly on the retina causing a blurred image.