Comparison of Optical versus Ultrasonic Biometry in Keratoconic Eyes

Purpose . To compare the measurements of optical versus ultrasonic biometry devices in keratoconic eyes. Materials and Methods . Forty-two eyes of 42 keratoconus (KC) patients enrolled in the study were examined. Clinical and demographic characteristics of the patients were noted, and detailed ophthalmological examination was performed. Following Pentacam measurements, central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), and axial length (AL) were obtained using the Lenstar and US biometer to determine the reproducibility of the measurements between the two devices in keratoconic eyes. The Bland-Altman method was used to describe the agreement between the two devices. Results . The Lenstar could not measure at least one of the biometric properties in one eye and did not automatically give the corrected ACD in 2/3 of our study population. The Lenstar measured CCT (average difference 5.4 ± 19.6  µ m; ICC = 0.90; P < 0.001), LT (average difference 0.13 ± 0.17 mm; ICC = 0.67; P < 0.001), and AL (average difference 0.10 ± 0.76 mm; ICC = 0.75; P < 0.001) thinner than US biometer, whereas it measured ACD (average difference 0.18 ± 0.17 mm; ICC = 0.85; P < 0.001) deeper than US biometer in keratoconic eyes. Conclusion . Although the difference between the measurements obtained using the two devices might be clinically acceptable, US biometry and Lenstar should not be used interchangeably for biometric measurements in KC patients.