An evaluation of the Hyde surgical astigmatic ruler

The Hyde Ruler, a semi-quantitative intraoperative keratometric device, was compared with the Bausch and Lomb keratometer by taking 50 paired measurements of induced astigmatism on a model cornea. The correlation between the two instruments was 0.884, and regression of the Hyde Ruler estimates on the Bausch and Lomb keratometer readings produced a slope of 0.732 with an intercept of -0.150 D. From the regression equation, a correction was applied to the Hyde Ruler estimates, resulting in 68.2% of the latter falling within 1.22 D or less of the Bausch and Lomb readings. We consider this accuracy to be acceptable for a semi-quantitative intraoperative keratometer, and should allow appropriate suture tensioning during cataract surgery to aid in early visual rehabilitation of the patient.