Comparison of corneal astigmatism and axis location in cataract patients measured by total corneal power, automated keratometry, and simulated keratometry

PURPOSE: To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry. SETTING: Siriraj Hospital, Mahidol University, Bangkok, Thailand. DESIGN: Prospective comparative study. METHODS: Eyes with previous ocular surgery or abnormalities were excluded. All patients were examined with the ARK 730A autokeratometer and the Galilei analyzer. The steepest and flattest corneal power along with the steepest axis of the TCP, automated keratometry, and simulated keratometry were recorded. Vector analysis (J0 and J45) was calculated. Analysis of variance with Bonferroni correction was performed for multiple comparisons. Outcome measures were the magnitude and axis location of astigmatism. RESULTS: One hundred eyes of 100 cataract patients were randomly selected. There was no statistically significant difference in the mean steepest axis between TCP (93.31 +/- 68.75 [SD]), automated keratometry (94.24 +/- 64.78), and simulated keratometry (92.42 +/- 64.30). However, the mean magnitude of astigmatism measured by TCP (1.23 +/- 0.75) was significantly higher than that measured by automated keratometry (0.93 +/- 0.68) (P = .01) but not than that measured by simulated keratometry (1.08 +/- 0.68) (P = .43); there was no statistically significant difference in J0 or J45. Twenty two (40%) of 54 eyes with more than 1.00 diopter of TCP astigmatism had more than 10 degrees of axis difference from automated keratometry. CONCLUSIONS: The magnitude of TCP astigmatism was higher than that of automated keratometry. The axis location was similar. However, there was more than 10 degrees of axis difference between automated keratometry and TCP in patients with high astigmatism. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2012; 38:2088-2093 (C) 2012 ASCRS and ESCRS