Original article
Comparison of Corneal Powers Obtained from 4 Different Devices

https://doi.org/10.1016/j.ajo.2009.04.028Get rights and content

Purpose

To assess the repeatability and comparability of anterior corneal power values obtained from the Galilei Dual Scheimpflug Analyzer (Ziemer, Port, Switzerland), Humphrey Atlas corneal topographer (Carl Zeiss, Jena, Germany), IOLMaster (Carl Zeiss), and a manual keratometer (Bausch & Lomb Inc, Rochester, New York, USA).

Design

Prospective, comparative study.

Methods

Prospectively, 20 subjects were enrolled. Three sets of corneal power measurements were obtained by a single observer using the Galilei, Atlas topographer, IOLMaster, and manual keratometer. Repeatability of the 3 measurements from each device was evaluated by means of coefficient of variation, standard deviation (SD), and intraclass correlation coefficient. An analysis of variance was used to compare the differences in corneal powers among devices. The Bland and Altman method also was performed to assess agreement in measurements between devices. Vector analysis was used to compare the astigmatism values obtained from different devices.

Results

For each device, the coefficient of variation of repeated measurements was lower than 0.22%. The SD of 3 repeated measurements ranged from 0.042 to 0.096 diopters (D). The intraclass correlation coefficients were higher than 0.99 in all devices. Mean central corneal powers were 43.80 D, 43.88 D, 43.92 D, and 43.76 D for the Galilei, Atlas, IOLMaster, and manual keratometer, respectively. SDs of the differences between devices ranged from 0.07 D for Galilei and IOLMaster to 0.14 D for Galilei and Atlas. For astigmatism, the mean astigmatism values for the Galilei, Atlas, IOLMaster, and manual keratometer were 0.54 D at 84 degrees, 0.51 D at 88 degrees, 0.62 D at 88 degrees, and 0.52 D at 87 degrees, respectively.

Conclusions

The corneal power measurements from these 4 devices were highly reproducible, comparable, and correlated.

Section snippets

Methods

Prospectively, 20 normal volunteers were recruited at the Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine. Exclusion criteria were: 1) history of prior intraocular and corneal surgery and trauma, 2) corneal and other ocular diseases that could affect outcomes, or 3) contact lens wear. The purpose, risks, discomfort, and steps of the study were explained to each subject, and written informed consent was obtained from all subjects.

Results

The mean age of the 20 subjects was 36 ± 12.5 years (± SD; range, 23 to 62 years). The subjects consisted of 6 males and 14 females. Ten right eyes and 10 left eyes of the 20 subjects underwent 3 measurements with each device.

Discussion

Accurate results from cataract surgery and procedures to correct corneal astigmatism require accurate measurements of corneal power. Norrby and Olsen demonstrated that inaccurate corneal power is a major cause of error in IOL calculations.18, 19 The purpose of this study was to assess the repeatability and comparability of corneal powers obtained from the Galilei, Humphrey Atlas corneal topographer, IOLMaster, and manual keratometer.

In our study, all devices demonstrated excellent

Mariko Shirayama, MD, graduated from faculty of Medicine, Kagawa University, Kagawa, Japan in 2003. She completed her ophthalmology residency at University of Tokyo Hospital. Dr Shirayama is currently the research fellow in Department of Ophthalmology, Baylor College of Medicine, Houston, Texas. Her research interests are cataract and refractive surgery.

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Mariko Shirayama, MD, graduated from faculty of Medicine, Kagawa University, Kagawa, Japan in 2003. She completed her ophthalmology residency at University of Tokyo Hospital. Dr Shirayama is currently the research fellow in Department of Ophthalmology, Baylor College of Medicine, Houston, Texas. Her research interests are cataract and refractive surgery.

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