Comparison of manual and automated methods to determine horizontal corneal diameter

Purpose: To compare 2 manual methods and 2 automated devices for measuring the horizontal corneal diameter (white-to-white [WTW] distance). Setting: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. Methods: In 100 eyes of 61 patients, the WTW distance was measured independently by 2 examiners using the following techniques: the Holladay-Godwin gauge, a measuring caliper, Zeiss IOLMaster, and Orbscan(R) II topography system (Bausch & Lomb). The results were compared with measurements on magnified slitlamp photographs of the anterior eye segment. Statistical evaluation was performed using the Bland-Altman method for comparison of measurement techniques. Results: The mean horizontal corneal diameter was 11.91 mm +/- 0.71 (SD) with the measuring caliper, 11.8+/-0.60 mm with the Holladay-Godwin gauge, 11.78+/-0.43 mm with the Orbscan II, and 12.02+/-0.38 mm with the IOLMaster. The coefficient of inter-rater repeatability was 1.30 for the caliper, 0.92 for the Holladay-Godwin gauge, 0.76 for the Orbscan II, 0.50 for the IOLMaster, and 1.16 for the manual measurement in anterior segment images. The results obtained with the caliper were statistically significantly different between the 2 examiners (P<.001). The measurements of examiner 2 using the caliper were significantly different from the measurements of the same examiner using the Holladay-Godwin gauge. This was not the case with the 2 automated devices. Conclusions: Automated measurement of the WTW distance provides more precise results than measurements using manual methods. The Zeiss IOLMaster had the highest reliability in measuring corneal diameter.