Agreement of corneal measurements between dual rotating Scheimpflug–Placido system and Placido-based topography device in normal and keratoconus eyes

Abstract

To compare the anterior corneal measurements between Placido-based topography and dual-Scheimpflug topography in healthy and keratoconus eyes. Optometry Research Group, Instituto Universitario de Oftalmobiología Aplicada, University of Valladolid, Valladolid, Spain. Comparative case series. The mean simulated keratometry (K), flat K, steep K, astigmatism power, corneal astigmatism axis, J0, J45, maximum corneal power point, and white-to-white (WTW) distance were collected and compared between healthy eyes and keratoconus eyes. The study evaluated in 56 healthy eyes and 56 keratoconus eyes. Placido-based topography underestimated all topographic values except J45 and WTW in healthy eyes and J0, maximum corneal power point, and WTW in keratoconus eyes, with statistically significant differences in astigmatism (healthy), flat K (keratoconus), axis (keratoconus), J0, J45, and WTW (P<.05). Healthy eyes showed better agreement (95% limits of agreement: simulated K -0.13 to 0.40; steep K -0.30 to 0.59; flat K -0.29 to 0.51; astigmatism -0.60 to 0.64; J0 -1.15 to 1.13; J45 -1.10 to 1.20; maximum corneal power point -0.70 to 1.17; WTW -0.96 to 0.76mm) than keratoconic eyes (simulated K -2.84 to 4.55; steep K -2.80 to 5.21; flat K -3.68 to 4.70; astigmatism -1.90 to 2.95; J0 -2.85 to 3.20; J45 -3.21 to 3.05; maximum corneal power point -7.00 to 4.51 D; WTW -1.00 to 0.88). Healthy eyes showed better agreement than keratoconus eyes between Placido-based and dual-Scheimpflug topography. Both instruments could be used interchangeably with caution in healthy eyes, but not in keratoconus management. None of the authors has a financial or proprietary interest in any material or method mentioned.