Purpose: This study was designed to compare higher order aberrations of the cornea and of the eye with inferior-superior (I-S) corneal topographic values in keratoconic eyes.
Methods: We studied 92 eyes from 78 subjects: 21 eyes of 14 subjects with suspected keratoconus, 23 eyes of 16 subjects with manifest keratoconus, and 48 eyes of 48 subjects without keratoconus using the L80 wave+, an instrument which can measure corneal topography and aberrations simultaneously with a large dynamic range making it possible to evaluate higher order aberrations to the seventh order of the Zernike polynomial function series.
Results: All ocular and corneal higher order aberrations were found to be significantly higher for keratoconic than normal eyes, but for suspected keratoconus the results were mixed. Corneal aberrations were higher than ocular aberrations due to compensation from the internal aberrations. For manifest keratoconus, the corneal and ocular vertical coma displayed the largest difference being 38.6 and 78.5 times higher, respectively, than normal eyes, while the largest differences for suspected keratoconus were only 5.3 and 4.0 times higher, respectively. On the other hand, inferior-superior dioptric asymmetry was 9.4 and 37.3 times higher for suspected keratoconus and keratoconic eyes, respectively, than normal eyes. The separation of normality curves between suspected keratoconus and normal eyes was 28.6% for I-S and 14.3% for both corneal vertical coma and corneal total coma.
Conclusions: Although corneal vertical coma and, to a lesser extent, ocular vertical coma were found to be good indicators for the detection of keratoconic eyes, the traditional corneal topographic value such as the inferior-superior dioptric asymmetry remains an important predictor for identifying suspected keratoconus. However, ocular vertical coma and ocular higher order total root mean square also represent a good means of identifying suspected keratoconus.