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？μm; ICC？=？0.90; ), LT (average difference 0.13？±？0.17？mm; ICC？=？0.67; ), and AL (average difference 0.10？±？0.76？mm; ICC？=？0.75; ) thinner than US biometer, whereas it measured ACD (average difference 0.18？±？0.17？mm; ICC？=？0.85; ) 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. 1. Introduction In modern corneal refractive and cataract surgery, precise measurement of corneal thickness and axial length is very important to achieve good refractive outcome. Ultrasound (US) biometry and laser biometric systems are widely used techniques in practice. A laser biometric system uses the principle of partial coherence interferometry and was found to be superior to the ultrasonic method in many ways [1, 2]. Keratoconus (KC) is a noninflammatory ectasia of the cornea in which thinning and protrusion of the cornea result in induced myopia, irregular astigmatism, and a deep anterior chamber [3]. Measurement of corneal thickness is essential in the diagnosis, classification, followup, and treatment of KC. Measurements of central corneal thickness (CCT) and anterior chamber depth (ACD) using optical biometry were previously found to be more reproducible and repeatable than those obtained using US biometry in both a normal population and also in keratoconic eyes [4–6]. It has been shown that myopia in KC is not only related to the change in corneal curvature but also associated with axial elongation [7, 8]. Biometric properties of the
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