Astigmatism is a antonym of stigmatism.

In optics terms the difference between stigmatism and astigmatism

is that stigmatism is image-formation property of an optical system which focuses a single point source in object space into a single point in image space while astigmatism is 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.

In pathology terms the difference between stigmatism and astigmatism

is that stigmatism is state of having stigmata while astigmatism is 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.