Research Of High Order Aberrations In Myopic Eyes Of Young People

Objective To analyze the distribution of the higher order aberrations in Chinese young people with myopia and to study the influence of refractive error and pupil size on the higher order aberrations; to evaluate the influence of correction with soft contact lenses(SCL) of myopia on HO A; and investigate the relationship between higher order aberrations and contrast sensitivity(CS) in myopic patients and provide data for the improvement of refractive correction.Methods Monochromatic aberrations of the whole eye were measured with a COAS Shack-Hartmann wavefront analyzer for each eye include 42 emmetropic eyes and 112 myopic eyes. The root mean square (RMS) values for the OS A standard up to 10th order for the subjects were taken with a natural pupil in all that each subject with pupil diameters of a lmm pupil sampling interval from 3 mm to 6mm were determined. HO As include all Zernike terms, the total high order aberration (tHOA), spherical aberration (SA), coma,3rd,4th,5th,6th order aberrations. Correlation analysis was performed to investigate the aberration with the change of refraction and pupil. Monochromatic aberrations of the whole eye were measured before and after wearing SCL for myopia correction. Each order aberrations and total high order aberrations from 3rd to 6th before and after correcting the lower order aberrations in myopia were compared, and the relationship of changes in refraction, Z20 and Z40 was analyzed respectively. The contrast sensitivity function after refract correction were observed in the model of day and night at near and far respectively to anlysis the relationship between higher order aberrations and contrast sensitivity.Results There was wide individual variability in HOAs of total eye with ranges of individual Zernike terms from -0.414 to 0.662μm. The lower order aberrations were major in wavefront aberrations while the higher order aberrations were near to zero except 3rd and 4th relatively. Each coefficient and range of aberration decrease as the increase of order, no presentation of linear correlation. The percentage of 3rd to 10th aberration were 38.1%,26.9%,10.6%,8.1%,5.7%,4.8%,2.9%,2.7%. The mean root-mean-square (RMS) values were (0.225±0.096)μm for tHOA, (0.117±0.071)μm for SA (Z40 and Z60), (0.172±0.093)μm for Coma(Z3-1,Z31) and (0.144±0.085)μm for Trefoil (Z3-3, Z33). The large amount of individual difference was obtained both in the pattern and magnitude of high-order aberrations in each refractive group from this studies that was found high variability of distribution of SA and trefoil statistically significant with 5mm aperture and 6mm aperture respectively(F=2.74,P=0.0454; F=3.93,P=0.0102). The values of RMS was increased correspondingly with pupil dilated from 3mm to 6mm in all types of aberrations,in particular 3rd and 4th order aberrations that were in creased significantly in the same eye. Sphere was related to wavefront aberration remarkably only(pearson r=-0.608, P=0.000)while not to SA(pearson r=-0.011, P=0.823). In circumstances of 5mm aperture and 6mm aperture, the RMS of SA,trefoil,tHOA and 4th,6th order aberrations across refractive error groups were statistically significant. Refraction correction with SCL yielded larger high order aberrations (t=2.125, P=0.039) including more coma (t=3.843, P=0.000) and less spherical aberration (t =-8.319, P=0.000). The change in spherical aberration was highly positively correlated with the changes in negative power of the contact lens (r=0.536, P=0.000). The contrast sensitivity of different model were significantly different, which showed that low spatial frequency:(CSnight/far>CSday/far>CSday/near); middle spatial frequency: (CSday/far>CSnight/far>CSday/near); high spatial frequency:(CSday/far>CSday/near>CSnight/far). SA affected middle and high spatial frequency(3cpd and 18cpd) at far model; coma affected all spatial frequency except 1.5cpd at near model. SA and coma were negative related to contrast sensitivity; Z4,2,Z4,4,Z5,-3 and Z6,-6 were positive related to contrast sensitivity.Conclusions There were some aberrations in normal eye, which is higher in high myopic eyes. The values and structure of aberrations were changed correspondingly with pupil, in particular 3rd and 4th order aberrations. The spherical aberration changes statistically with SCL for refract correction. Spherical aberration had negative correlation with CS at far model; Coma had negative correlation with CS at near model. Every element of higher order aberrations interacts on each other.