OBJECTIVE: To study the repeatability and scale increments of automated keratometry and their influence on the use of the toric intraocular lens (IOL) and on astigmatism correction. METHOD: The study enrolled 131 eyes of 82 patients. Preoperative corneal astigmatism was measured in the different (0.01D and 0.25D) scale increment setting of automated keratometer on separate days. An arithmetic astigmatism in 0.25 D scale increment was also calculated from that of 0.01 D scale increment. These three types of corneal astigmatism were comparatively appraised with a web-based calculator, evaluating indication and style selection of the toric IOL and simulated residual astigmatism. RESULTS: Different scale increments caused no significant difference in simulated residual astigmatism. The repeatability of calculated IOL style selection and axis location was low in eyes with mild astigmatism. True standard deviation of test-retest discrepancy in the size of corneal astigmatism was 0.293 D. CONCLUSION: In mild astigmatism, the effectuation of the toric IOL, such as IOL style selection and axis location, was ineffective. However, the scale increment of 0.25 D presented moderate sensitivity. The refinement of corneal astigmatism measurement and development of algorithm would be the key to more accurate astigmatism correction with a toric IOL implantation.
OBJECTIVE: To study the repeatability and scale increments of automated keratometry and their influence on the use of the toric intraocular lens (IOL) and on astigmatism correction. METHOD: The study enrolled 131 eyes of 82 patients. Preoperative corneal astigmatism was measured in the different (0.01D and 0.25D) scale increment setting of automated keratometer on separate days. An arithmetic astigmatism in 0.25 D scale increment was also calculated from that of 0.01 D scale increment. These three types of corneal astigmatism were comparatively appraised with a web-based calculator, evaluating indication and style selection of the toric IOL and simulated residual astigmatism. RESULTS: Different scale increments caused no significant difference in simulated residual astigmatism. The repeatability of calculated IOL style selection and axis location was low in eyes with mild astigmatism. True standard deviation of test-retest discrepancy in the size of corneal astigmatism was 0.293 D. CONCLUSION: In mild astigmatism, the effectuation of the toric IOL, such as IOL style selection and axis location, was ineffective. However, the scale increment of 0.25 D presented moderate sensitivity. The refinement of corneal astigmatism measurement and development of algorithm would be the key to more accurate astigmatism correction with a toric IOL implantation.