Agreement between Pentacam and videokeratography in corneal power assessment

To investigate agreement between a rotating Scheimpflug camera (Pentacam, Oculus Optikgeräte GmbH) and two corneal topographers (TMS-2 Topography System, Tomey; and Keratron Scout, Optikon 2000 SpA) in measuring the corneal power of normal eyes.

The mean corneal powers calculated by simulated keratometry (SimK) with each topographer were compared to those provided by the Pentacam in 71 patients. Specifically, the corneal power values of the Pentacam included in this analysis were the SimK (calculated using the measured anterior corneal radius and standard keratometric index of 1.3375) and the True net power (calculated using the anterior and posterior corneal curvatures and Gaussian optics formula for thick lenses, where the actual refractive index of the air, cornea, and aqueous humor are entered). Bland-Altman plots were used to investigate agreement and analysis of variance (ANOVA) was performed to detect statistical differences.

Although ANOVA did not disclose a statistically significant difference among the mean SimK values (TMS-2: 43.20 +/- 1.51 diopters [D], Keratron Scout: 43.29 +/-1.48 D, Pentacam: 43.25 +/- 1.53 D), the 95% limits of agreement between the TMS-2 and Pentacam and between the Keratron Scout and Pentacam were wide (-1.05 to +0.94 D and -0.95 to +1.02 D, respectively). Agreement was even poorer when considering the mean True net power (42.00 +/- 1.54 D), which was significantly lower than the mean Pentacam SimK (P < .001).

Although corneal topography and the Pentacam provide similar SimK values, their data should not be used interchangeably as only moderate agreement exists between them. Corneal power values calculated by the True net power are significantly lower than any SimK and cannot be entered into intraocular lens power formulas.