Monochromatic aberrations of the human eye and myopia

Background: The relationship between monochromatic aberrations of the human eye and myopia has been investigated extensively over the past decade or so but the results are inconclusive. Wide age range, narrow refractive error range and large individual variations are common confounding factors in previous studies. To address these shortcomings, we conducted a two-part study. The first part set out to determine whether the monochromatic aberrations in myopic eyes are different from those in the non-myopic eyes in adults. Subjects were drawn from a narrow age band to minimise the confounding effect of age. The second part of this study compared the monochromatic aberrations of the more myopic and less myopic eyes of anisometropes. Methods: Monochromatic aberrations were measured for 5 mm pupils using the Complete Ophthalmic Analysis System (COAS) Wavefront Analyzer in 116 subjects with refractive spherical equivalent between -10.38 D and +1.38 D and in 26 anisometropes. Measurements were done in a dark room with natural pupils. The refractive errors, corneal curvatures and axial lengths of the eyes were measured under natural accommodation. Results: Highly myopic eyes had significantly smaller root mean square (RMS) values of fourth order (p = 0.015) and spherical aberrations (p = 0.009) than non-myopic eyes. The correlation coefficient was 0.2354 (p = 0.011) between fourth-order aberrations and refractive spherical equivalents and 0.2817 (p = 0.002) between spherical aberration and refractive spherical equivalents. Less myopic eyes of the anisometropes showed significantly larger total higher-order, third-order and spherical aberrations than the more myopic eyes (p < 0.05, p < 0.05 and p < 0.01, respectively). Conclusions: Our study shows that spherical aberration is associated with refractive error. More myopic eyes tended to have smaller amounts of spherical aberration, however, the ‘cause or effect’ question remains. Longitudinal studies are needed to further investigate the relationship between monochromatic aberrations and refractive development.