Comparison of portable automated keratometry and manual keratometry for IOL calculation

Purpose: To compare the accuracy of portable automated keratometry (PAK) with that of manual keratometry (MK) in measuring corneal power for intraocular lens calculations. Setting: Wilford Hall Medical Center, San Antonio, Texas, USA. Methods: In Part 1 of the study, five ophthalmic technicians performed keratometric analysis in 20 eyes in 10 volunteers using both manual and automated methods to determine the relative accuracy and reproducibility of each instrument. In Part 2, both MK and PAK were prospectively performed in 11 patients having cataract surgery to compare the accuracy of each instrument in predicting postoperative refractive outcome. Results: The difference between instruments in determining the average corneal power in all eyes was less than 0.10 diopter (D) (MK = 43.84 D, PAK = 43.93 D). Portable keratometry demonstrated less variability in measurements in each eye (average standard deviation, MK = 0.30 D, PAK = 0.11 D; average range, MK = 1.08 D, PAK = 0.44 D). The mean absolute refractive error (difference between the actual refractive outcome and predicted refractive outcome) was 0.37 D ± 0.30 (SD) using MK values and 0.45 ± 0.19 D using PAK values. Conclusions: Portable automated keratometry is a simple keratometric technique that appeared to be as accurate as but with less variability than manual keratometry in determining corneal power for cataract surgery.