Intraoperative semiquantitative keratometry using the keratoscopic astigmatic ruler

Intraoperative keratometry enables the surgeon to set an appropriate amount of corneal astigmatism with the suture tension. Errors in estimating or measuring the astigmatism can occur with hand-held keratometers because the distance an object is held from an astigmatic cornea influences the shape of the elliptical image. Thus hand-held instruments should be held at a calibrated distance. We have designed a new hand-held keratometer, the keratoscopic astigmatic ruler, to assess the magnitude of corneal astigmatism. It consists of a rack of elliptical keratoscopic lenses corresponding to increasing magnitudes of astigmatism and is made from inexpensive autoclavable injection-molded plastic. The ruler's keratoscopic lenses refract light, creating a real aerial image above the cornea that produces a bright and easily determined corneal reflection. The ruler incorporates a sight to allow the user to hold the ruler at the correct distance.