Optical aberrations of the human anterior cornea

Purpose: (1) To investigate the distribution of anterior corneal higher-order aberrations (HOAs, 3rd to 6th orders) in the population; (2) to evaluate the symmetry of anterior corneal aberrations between right and left eyes of individuals; and (3) to study the variations in anterior corneal aberrations with aging. Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Methods: Using the CTView program (Sarver and Associates, Inc.), corneal HOAs were computed from the central 6.0 mm zone of the corneal topographic maps (Humphrey Atlas, Carl Zeiss, Inc.) of 228 eyes of 134 subjects (mean age 50 years ± 17 (SD); range 20 to 79 years; manifest spherical equivalent between –3.0 and +3.0 diopters [D]). Correlation analysis was performed to investigate the aberration symmetry between the right and left eyes and to assess the association between anterior corneal HOAs and age. Results: There was wide individual variability in aberrations with ranges of individual Zernike terms from −0.579 to +0.572 μm. The mean coefficient of the 4th-order spherical aberration (SA) (Z40) was 0.280 ± 0.086 μm and was positive in all corneas. The mean root-mean-square (RMS) values were 0.479 ± 0.124 μm for HOA, 0.281 ± 0.086 μm for SA (Z40and Z60), and 0.248 ± 0.135 μm for coma (Z3−1, Z31, Z5−1, and Z51). Moderate to high correlations were found between right and left eyes for HOA, SA, and coma (Pearson r = 0.565, 0.751, and 0.565, respectively; all P<.001); 8 of the 9 Zernike terms in the 3rd and 4th orders were significantly correlated between eyes (Bonferroni correction P′<.05/22). Higher-order aberration RMS and coma RMS increased with aging (r = 0.434 and 0.290, respectively; both P<.001); SA RMS was not correlated with change in age (r = 0.034). Conclusion: Anterior corneal wavefront aberrations varied greatly among subjects and increased slightly with aging. All corneas had positive 4th-order SAs, and the values did not change with aging. A moderate to high degree of mirror symmetry existed between right and left eyes.