Repeatability of placido-based corneal topography in keratoconus.

ABSTRACT

PURPOSE: To determine and compare the repeatability of a Placido-based corneal topography (Oculus Keratograph) in a sample of healthy and keratoconus eyes. METHODS: The corneal topography, determined using the Oculus Keratograph, of 25 healthy and 25 keratoconus eyes was assessed three consecutive times. A single randomized eye was included per patient. Coefficient of variation (CV) of the eccentricity, corneal diameter, index of surface variance, index of vertical asymmetry, keratoconus index (KI), smallest sagittal curvature radius (Rmin), aberration coefficient, and maximum corneal power and minimum corneal power (diopters) in the 3.0-mm zone in addition to the maximum corneal power point (MCPP) (diopters) were calculated and compared between healthy and keratoconus eyes. RESULTS: Healthy eyes showed lower topographic values (p < 0.05) than keratoconus eyes, except with regard to the Rmin value. Corneal diameter (p = 0.45) was similar in both groups. All variables showed good CVs in healthy and keratoconus eyes (maximum corneal power [0.21 and 0.47%, respectively], minimum corneal power [0.19 and 0.36%], MCPP [0.22 and 0.77%], corneal diameter [0.27 and 0.33%], index of surface variance [4.82 and 3.10%], index of vertical asymmetry [7.05 and 3.80%], KI [0.29 and 0.72%], Rmin [0.53 and 0.78%], and aberration coefficient [0 and 4.00%]) except for the eccentricity CV (5.79 and 14.53%, respectively). Statistically significant differences (p < 0.05) between healthy and keratoconus groups were found for all variables, except with respect to the MCPP, eccentricity, corneal diameter, KI, and Rmin (p > 0.07). CONCLUSIONS: The Oculus Keratograph provides repeatable measurements of corneal topography in healthy and keratoconus eyes. These results could improve the topographical diagnosis of keratoconus, thus aiding in patient management.