A COMPARISON OF 2 SEMIQUANTITATIVE SURGICAL KERATOMETERS - THE MODIFIED HYDE RULER AND THE BARRETT KERATOSCOPE WITH ASTIGMATIC DIAL

The Hyde astigmatic ruler is an inexpensive, semiquantitative, hand-he ld, surgical keratometer that we modified by geometrically calculating the correct shape of its ellipses. The Barrett keratoscope is a cheap , disposable, qualitative keratometer that, unlike the Hyde ruler, pro duces a bright corneal image. We designed a transparent overlay, or '' astigmatic dial,'' to use with the keratoscope. This overlay determine s the magnitude of astigmatism and sets the distance the keratoscope i s held from the cornea by direct comparison with the corneal image. Us ing a model cornea, we compared our modified Hyde ruler with the Barre tt keratoscope and astigmatic dial to determine the accuracy of measur ement provided by each. Both instruments had good predictive values fo r the true astigmatism; however, the Barrett keratoscope/astigmatic di al provided more consistent measurements of the astigmatism. We believ e the keratoscope and dial provide a cheap, convenient, and accurate a lternative to the more expensive microscope-mounted keratometers.