Comparability of an Image-guided System with Other Instruments in Measuring Corneal Keratometry and Astigmatism

PURPOSE: To test whether keratometry (K) and astigmatism measurements provided by the Verion Reference Unit (an image-guided system) compared well with the Tonoref II automated tonometer-refractometer, IOLMaster partial coherence interferometry (PCI) biometer, AL-Scan optical biometer, Pentacam rotating Scheimpflug camera, and OPD Scan III wavefront aberrometer. SETTING: Augenklinik am Neumarkt, Cologne, Germany. DESIGN: Retrospective case series. METHODS: Patients having routine cataract surgery had standard preoperative assessment including biometry measurement with all study devices. The K values, power of astigmatism, axis, and the lens power of an imaginary intraocular lens (IOL) were analyzed for each device. RESULTS: One hundred five eyes of 62 patients with a mean age of 68.5 years +/- 11.9 (SD) (range 27.2 to 89.7 years) were included in the study. The mean differences in flat K readings between the image-guided system and the tonometer-refractometer, PCI biometer, optical biometer (2.4 and 3.2 mm), rotating Scheimpflug camera, and wavefront aberrometer were -0.03 mm, 0.00 mm, 0.01 mm (both 2.4 and 3.2 mm), -0.03 mm, and -0.01 mm, respectively (P < .001). Differences were slightly greater for steep K readings as follows: -0.04 mm, -0.01 mm, -0.02 (optical biometer 2.4 mm), -0.03 mm (optical biometer 3.2 mm), -0.04 mm, and -0.06 mm, respectively (P < .001). The calculated power of an imaginary IOL from the study devices fell within 0.28 diopter of one another (P > .05). CONCLUSIONS: The image-guided system compared well with and provided astigmatism measurements similar to those of currently available diagnostic measurement devices. This system can aid appropriate preoperative IOL power calculations. FINANCIAL DISCLOSURES: Drs. Schultz, Oberheide, and Kermani have received honoraria from Alcon Pharma GmbH for corporate presentations.