Corneal higher order aberrations:: A method to grade keratoconus

PURPOSE: To use the anterior corneal surface higher order aberrations as a tool to detect and grade keratoconus using corneal map analysis videokeratoscopy. METHODS: A prospective observational comparative study of 80 eyes was performed. The eyes were divided into two groups. Group A comprised 40 eyes of 20 asymptomatic individuals with no ocular pathology. Mean sphere was -0.03 diopters (D) (range: +0,75 to -0.75 D), mean cylinder was -0.27 D, mean average K was 43.28 D, and mean uncorrected Visual acuity (UCVA) was 1.01. Group B comprised 40 eyes of 25 patients with keratoconus. Mean sphere was -3.70 D (range: +2.00 to -10.00 D), mean cylinder was -3.82 D, mean average K was 49.29, and mean best spectacle-corrected visual acuity (BSCVA) was 0.61. RESULTS: In group A, mean root-mean-square (RMS) of spherical (Z(4) and Z(6)), coma-like (Z(3), Z(5), and Z(7)), and higher order aberrations (Z(3-7))were 0.38 mu m, 0.35 mu m, and 0.52 mu m, respectively. In group B, mean RMS of spherical, coma-like, and higher order aberrations were 1.06 mu m, 2.90 mu m, and 3.14 mu m, respectively, for a 6.0-mm simulated pupil diameter. Mean RMS differences between the two groups were 0.68 mu m (P <=.0002), 2.55 mu m (P <=.0001), and 2.61 mu m (P <=.0001) for spherical, coma-like, and total higher order aberrations respectively. In group B, according to Amsler-Krumeich classification, the mean RMS of coma-like aberration was 1.87 mu m in grade I (14 eyes), 2.97 mu m in grade II (11 eyes), 3.46 mu m in grade III (12 eyes), and 5.20 mu m in grade IV (3 eyes). CONCLUSIONS: Corneal higher order aberrations especially coma-like aberrations, are significantly higher in eyes with keratoconus than normal eyes. Coma-like aberrations, with the aid of a corneal aberrometry map are good indicators for early detection and grading keratoconus.