The surgical astigmatic ruler.

A simple device for evaluating the corneal astigmatism present at the conclusion of ocular surgery is described. Directing the coaxial light from the operating microscope through the ruler's round aperture will create an elliptical reflex from the cornea that indicates the presence of astigmatism. Successive apertures in the ruler present known elliptical light reflexes to the cornea, and the surgeon can select the aperture that converts the corneal reflex to a circular appearance. The dioptric marking of the aperture indicates the approximate value of the astigmatism on the cornea.