Pentacam posterior and anterior corneal aberrations in normal and keratoconic eyes

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

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.

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.

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.