Corneal Higher Order Aberrations: A Method to Grade Keratoconus

ABSTRACT 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^sub 3-7^) were 0.38 µm, 0.35 µm, and 0.52 µm, respectively. In group B, mean RMS of spherical, coma-like, and higher order aberrations were 1.06 µm, 2.90 µm, and 3.14 µm, respectively, for a 6.0-mm simulated pupil diameter. Mean RMS differences between the two groups were 0.68 µm (P≤.0002), 2.55 µm (P≤.0001), and 2.61 µm (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 µm in grade I (14 eyes), 2.97 µm in grade II (11 eyes), 3.46 µm in grade III (12 eyes), and 5.20 µm 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 of keratoconus. [J Refract Surg. 2006;22:539-545.]