Keratometry versus total corneal refractive power: Analysis of measurement repeatability with 5 different devices in normal eyes with low astigmatism

To analyze the repeatability of corneal astigmatism measurements with 2 autokeratometers (IOLMaster 500 and Lenstar LS 900), 2 Placido topographers (Keratron Scout and Atlas 9000), and a Scheimpflug tomographer (Pentacam HR).Department of Ophthalmology, Goethe University, Frankfurt, Germany.Prospective case series.The inclusion criteria were a minimum age of 18 years, corneal astigmatism of 3.00 diopters or less, and patient's consent to participate in the study. The main exclusion criteria were corneal pathologies, trauma, previous surgery, hard contact lens wear in the previous 3 months, and soft contact lens wear in the previous 6 weeks. In addition to manifest refraction and visual acuity measurements, all subjects had 2 full measurements of 1 eye using each device. Anterior corneal astigmatism and total corneal refractive power via calculations derived from the Scheimpflug tomographer were evaluated. Statistical analysis was performed using the Bland-Altman method and multiple linear regression analysis.Forty-five eyes of 45 subjects (mean age 53.11 years ± 10.43 [SD]; 23 left eyes; 33 women) were included. The mean intermeasurement differences were approximately zero for all devices. The relative coefficient of repeatability of anterior corneal astigmatism, steep axis, and the vector analysis parameter J180 were lowest with the Scheimpflug tomographer. Total corneal refractive power measured with the Scheimpflug tomographer showed the highest repeatability in the larger diameter zones.The Scheimpflug tomographer yielded higher repeatability of corneal astigmatism measurements, with total corneal refractive power measurements being as repeatable as established metrics.Dr. Kohnen receives research support from Abbott Medical Optics Inc., Alcon Pharma GmbH, Bausch & Lomb GmbH, Carl Zeiss Meditec Vertriebsgesellschaft mbH, Hoya Surgical Optics GmbH, Oculus Optikgeräte GmbH, and Schwind eye-tech-solutions GmbH and Co. KG. He receives travel reimbursement, lecture fees and is a consultant to Abbott Medical Optics Inc., Alcon Pharma GmbH, Carl Zeiss Meditec Vertriebsgesellschaft mbH, Geuder AG, Oculus Optikgeräte GmbH, Schwind eye-tech-solutions GmbH and Co. KG, TearLab Corp., Thieme Compliance, and Ziemer Ophthalmic Systems AG. None of the other authors has a financial or proprietary interest in any of the materials or methods mentioned.