The purpose of the present study is to determine the repeatability of anterior curvature of 5 corneal rings (1-5 mm from the corneal center) in keratoconus patients obtained by the Orbscan and Eyesys instruments and to determine the level of agreement of curvature measurements between two instruments.

In this prospective study, anterior curvatures of 5 corneal rings were measured using Orbscan and Eyesys in 48 right eyes of 48 keratoconic patients. The mean age of patients was 31.6±4.7 and the grades of keratoconus of patients according to the maximum keratometry were mild (≤50 D), moderate (50-55D) and severe (≥55D). Statistical analysis was performed using Intraclass Correlation Coefficient and Repeated measures ANOVA for repeatability of each device. Pearson's correlation coefficient, paired t test and Bland-Altman plot were also used for comparison of two techniques.

In this study, the ICC showed high repeatability for measurements of each devices (ICC Eyesys=0.99, ICC Orbscan?0.95, P<0.0001) in all corneal rings. According to repeated measures ANOVA, there was no significant difference between the repeated measurements of each device in all corneal rings. The Pearson's correlation analysis showed high correlation between the measurements of Orbscan and those of Eyesys (r?0.84, P<0.0001) in all rings. According to the paired t test, there was a significant difference in curvature measurements of Eyesys and those of Orbscan in all corneal rings (P<0.001). Also, the Bland-Altman plots showed low agreement between curvature measurements of two devices in all corneal rings.

The present study showed that the anterior curvature measurements obtained by each of Orbscan and Eyesys instruments were repeatable in all corneal rings. Anterior curvature measurements of 5corneal rings obtained by Eyesys were steeper than those obtained by Orbscan and the two devices could not be replaced for anterior corneal curvature measurement in keratoconic eyes.