To determine the agreement and validity of keratometric measurements in children with the Nidek ARK-510A auto-refractokeratometer (ARK) compared to Pentacam and Biograph.

This population-based cross-sectional study was conducted on 5620 schoolchildren aged 6 to 12 years in Shahroud, Iran. All children had visual acuity tests, objective and subjective refractions. Minimum keratometry and maximum keratometry values were compared among three devices: Nidek ARK-510A, Pentacam and Biograph. Minimum and maximum keratometry values were compared by calculation of the 95% limits of agreement (LoA) between devices.

After applying the exclusion criteria, 4215 right eyes were enrolled into the study. Mean minimum keratometry with ARK, Pentacam, and Biograph was 43.13 ±1.51, 43.14 ±1.48, and 42.87 ±1.46 diopters (D), respectively, and mean maximum keratometry was 43.97 ±1.59, 44.00 ±1.56, and 43.75 ±1.54 D, respectively. ARK overestimated minimum and maximum keratometry by 0.25 ±0.37 and 0.22 ±0.41, respectively, compared to Penatcam. The LoA between ARK and Pentacam for minimum and maximum keratometry measurements were -0.98 to 0.47 D and -1.02 to 0.57 D, respectively. The LoA between ARK and Biograph for minimum and maximum keratometry measurements were -0.70 to 0.72 D and -0.79 to 0.85 D, respectively. The agreement between devices was best in emmetropes and worst in hyperopes.

Keratometry measurement with ARK was not significantly different from Pentacam and Biograph, and this device can be used to determine keratometry in screening programs for children especially in emmetropes. The results with ARK are not interchangeable with the other two devices in hyperopes