Repeatability of Measurements Obtained With 3 Topographers in Keratoconic and Normal Corneas
Purpose
To assess the repeatability of the corneal topograph function of Orbscan II, OPD-Scan III and iTrace in keratoconus and to compare it to the repeatability of measurements obtained in a control group of normal patients.
Methods
Prospective cohort study. Patients were prospectively recruited from the Department of Refractive Surgery at the Rothschild Ophthalmic Foundation, Paris, France between November 2011 and May 2012. Main outcome measure: repeatability limit of keratometric readings.
Results
Fifty-nine keratoconic eyes of 34 patients and 54 normal eyes of 27 subjects were included in this study. For all studied parameters, repeatability limit was higher, and thus the repeatability was lower, in keratoconic eyes compared to normal eyes, with the 3 topographers used. For maximum keratometry measurement, it was 1.73, 1.49 and 1.24 diopters in patients group and 0.61, 0.37 and 1.02 diopters in control group with Orbscan II, OPD-Scan III and iTrace, respectively. For minimum keratometry measurement, it was 1.45, 1.62 and 1.42 diopters in patients group and 0.65, 0.32 and 0.91 diopters in control group, respectively.
Conclusion
Topographies performed in keratoconic eyes are less reliable than those performed in normal eyes. Values of the thresholds of keratometric changes used to acertain keratoconus progression might be reconsidered. Caution should be taken when interpreting the topographies of such patients, and their higher variability should be taken into account.