Comparability of an image-guided system with other instruments in measuring corneal keratometry and astigmatism

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.

Augenklinik am Neumarkt, Cologne, Germany.

Retrospective case series.

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.

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).

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.

Drs. Schultz, Oberheide, and Kermani have received honoraria from Alcon Pharma GmbH for corporate presentations.