Repeatability and comparability of keratometry measurements obtained with swept-source optical coherence and combined dual-Scheimpflug Placido-disc–based tomography

PURPOSE To assess the repeatability of keratometric measurements obtained using a reflectance and swept-source based optical coherence tomography (SS-OCT) biometer and to compare these values to those obtained with a dual Scheimpflug-Placido disc based tomographer/topographer. SETTING Department of Ophthalmology, Penn State College of Medicine, Hershey, Pennsylvania, USA. DESIGN Prospective consecutive case series. METHODS Patients undergoing cataract evaluation were prospectively enrolled. Surgery-naive eyes without corneal pathology were measured 3 times with the reflectance/SS-OCT biometer and once with the dual Scheimpflug-Placido (S-P) disc tomographer/topographer. Intradevice repeatability for anterior (K), posterior (PK), and total corneal keratometry (TK) readings were evaluated using within-eye standard deviations, test-retest repeatability, coefficients of variance, and intraclass correlation coefficients (ICCs). Bland-Altman analysis was used to assess agreement between devices. RESULTS Eighty-two eyes from 48 patients met inclusion criteria. The test-retest repeatability (TRT) for the anterior, posterior, and total corneal powers were 0.33, 0.08, and 0.36 diopter (D), respectively. TRT for the anterior, posterior, and total keratometric astigmatism were 0.58, 0.14, and 0.64 D, respectively. Anterior keratometric indices had higher ICCs than posterior indices. Bland-Altman analysis revealed that the SS-OCT consistently reported flatter posterior corneal curvatures than the S-P. CONCLUSIONS The SS-OCT posterior keratometric measurements contain more noise (lower ICCs), but still have lower within-eye standard-deviations and TRTs than that of anterior measurements. This may be due to the small index of refraction change at the cornea-aqueous interface. While keratometric indices from the 2 devices are highly correlated, measurements taken using SS-OCT and S-P devices were not interchangeable.