Pentacam posterior and anterior corneal aberrations in normal and keratoconic eyes.

Purpose: The aim was to evaluate the anterior and posterior corneal aberrations provided by the Pentacam system in normal and early to moderate keratoconic eyes.

Methods: Fifteen normal eyes (normal group, mean age 32.60 +/- 7.45 years) and 15 eyes with the diagnosis of keratoconus (keratoconus group, mean age 29.07 +/- 8.66 years) were included in this study. All eyes received a comprehensive ophthalmologic examination including corneal topographic analysis with the Pentacam system. Keratometric, best-fit sphere and corneal aberrometric data were recorded and analysed. Root mean square values (RMS) were calculated for primary coma and coma-like aberrations.

Results: Statistically significant differences were found in all anterior aberrometric parameters (all p < 0.02), except for horizontal primary and secondary coma Zernike terms (p = 0.61 and 0.72). Regarding posterior corneal surface, statistically significant differences among groups were found in primary spherical aberration, primary vertical coma, coma RMS and coma-like RMS (all p < 0.01). In the normal group significantly higher levels of primary vertical coma, spherical aberration, coma and coma-like RMS were found for the posterior corneal surface (all p < 0.04). In the keratoconus group, only significant differences among anterior and posterior corneal surfaces were found in coma RMS, coma-like RMS and vertical coma (all p < 0.01). These higher levels of aberrations for the posterior corneal surface do not agree with the theoretical optical properties of this surface.

Conclusions: With the Pentacam system, higher levels of vertical coma, primary coma and coma-like aberrations are present in keratoconic eyes compared to normal eyes. The values provided by this device for posterior corneal aberrations are erroneous.