Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

PURPOSE: To assess the repeatability and agreement of corneal power, corneal astigmatism, axis location, and astigmatic vector component measurements using an autokeratometer and a corneal topographer in healthy subjects. SETTING: Department of Ophthalmology, Kitasato University, Kanagawa, Japan. DESIGN: Evaluation of diagnostic test or technology. METHODS: Keratometric readings were obtained with an ARK-700A autokeratometer and an Atlas corneal topographer. Measurement repeatability and agreement in corneal power (flattest and steepest meridians), mean corneal power, corneal astigmatism, axis location, and astigmatic vector components (Jackson cross-cylinders J0, J45) between the devices were evaluated. RESULTS: The repeatability of both devices in the flattest and steepest meridians, mean corneal power, corneal astigmatism, axis location, J0, and J45 was high. The 95% limits of agreement between the 2 devices were from -0.51 to 0.48 diopters (D) for the flattest meridian, from -0.74 to 0.71 D for the steepest meridian, from -0.56 to 0.53 D for the mean corneal power, from -0.58 to 0.58 D for corneal astigmatism, from -15.3 to 17.5 degrees for axis location, from -0.32 to 0.30 D for J0, and from -0.22 to 0.20 D for J45. In eyes with a small amount of astigmatism, there was wider disagreement in axis location between the 2 devices. CONCLUSIONS: Both devices provided excellent repeatability and comparability of corneal powers and corneal astigmatism, suggesting they can be used interchangeably for measurement of these corneal variables in healthy eyes. However, disagreement in axis location between the 2 devices was not negligible in some eyes, especially in those with low astigmatism.