Comparative Analysis of Corneal Refraction and Astigmatism Measured with Autokeratometer, IOL Master, and Topography

ABSTRACT

PURPOSE: To comparatively analyze the repeatability and consistency between different methods of measuring corneal refraction and astigmatism in order to precisely determine the toric intraocular lens target. METHODS: The medical records of 254 eyes of 192 persons were retrospectively reviewed to compare the repeatability of corneal refraction measured with autokeratometer, IOL Master, and topography. The axis and the amount of the astigmatism were compared between these methods. The differences between the estimated spherical equivalents using measured corneal refractive values and the actual spherical equivalents after cataract surgery were compared to evaluate the expected astigmatic error of each measurement. RESULTS: The average corneal refraction was greater with topography than with IOL Master or autokeratometer. Astigmatism calculated with IOL Master was greater than that measured with topography or autokeratometer. The mean coefficient of variation for mean corneal refraction was 0.19% with autokeratometer, which was smaller than that with IOL Master or topography. In patients with more than 1.5D of astigmatism, there were no significant differences in the axis measured by each instrument. The expected spherical error in IOL calculation was smaller with the measured values from IOL Master and autokeratometer than were those with topography. CONCLUSIONS: The repeatability of measurements for corneal refraction and astigmatism was significantly higher using the autokeratometer and IOL Master, with the highest astigmatic value observed with the IOL master. The axis of astigmatism for each method was consistent in the patients with more than 1.5D of astigmatism.