N. Morlet et Pa. Lindsay, INTRAOPERATIVE SEMIQUANTITATIVE KERATOMETRY USING THE KERATOSCOPIC ASTIGMATIC RULER, Journal of cataract and refractive surgery, 21(6), 1995, pp. 616-619
Intraoperative keratometry enables the surgeon to set an appropriate a
mount of corneal astigmatism with the suture tension. Errors in estima
ting or measuring the astigmatism can occur with hand-held keratometer
s because the distance an object is held from an astigmatic cornea inf
luences the shape of the elliptical image. Thus hand-held instruments
should be held at a calibrated distance, We have designed a new hand-h
eld keratometer, the keratoscopic astigmatic ruler, to assess the magn
itude of corneal astigmatism. It consists of a rack of elliptical kera
toscopic lenses corresponding to increasing magnitudes of astigmatism
and is made from inexpensive autoclavable injection-molded plastic. Th
e ruler's keratoscopic lenses refract light, creating a real aerial im
age above the cornea that produces a bright and easily determined corn
eal reflection. The ruler incorporates a sight to allow the user to ho
ld the ruler at the correct distance.