Definition of "astigmatically" []

• In an astigmatic manner, as when, in the formation of images, the beam of light is oblique to the axis of a lens system or mirror, or when the reflecting or refracting surface has two different curvatures.

The Century Dictionary (Public Domain)

• "This is incorrect, because the plano (i.e. no refractive power) surface of the clear glass does not bend the incoming light before it is reflected, otherwise the mirror would magnify, minify, or distort astigmatically."