| Objective:To analyse characteristic and distribution of higher-order aberration in myopia, and the correlations of higher-order aberration between the anterior cornea and posterior cornea, between cornea and the whole eye, and possible effective factors. To investigate changes in the posterior corneal surface after LASIK and analyze relevant factors for the changes, in order to acsess the safety and predictability of LASIK.Methods:One hundred and eight normal cases (197 eyes) were recruited in the Refractive Center of Tianjin eye hospital. Corneal aberration and ocular aberration were measured by Pentacam and WaveScan respectively. To analyze the correlations between the related factors and Zernike terms.102 eyes of 52 patients who had LASIK were examined. Corneal topography of the posterior corneal surface was obtained with Pentacam system preoperatively and 1 month and 3 months postoperatively. The factors relevant to the changes in the posterior corneal surface were analyzed before and after LASIK.Results:1. The mean Zernike aberrations for the cornea and whole eye tend to become progressively smaller as the order increased.2. There were statistically significant differences between anterior and posterior cornea in vertical coma, spherical and tetrafoil aberration (P<0.05).There was statistically significant negative relationship between anterior and posterior corneal surface in coma,spherical aberration,S3,S4,S5 and S6 (P<0.01).3. The posterior corneal RMS errors were much smaller than the anterior surface, and the entire corneal RMS was compensated by the anterior and posterior cornea.4. Rh had statistically significant relationship with ocular Sh,ocular S4,ocular S5,ocular S6,CB Sh,CB S3,CB S5 (P<0.05). Rv had statistically significant relationship with ocular Sh,ocular S4,corneal Sh,CF Sh,CB Sh (P<0.05).5. IOP had statistically significant relationship with CF S3,CF S6,CB S5,CB S6,cornea S3 and cornea S6 (P<0.05).6. There was no statistically significant relationship between corneal thickness and Zernike aberrations for the cornea and whole eye (P>0.05).7. There was no significantly statistical difference of higher-order aberration RMS value between male and female(P>0.05).8. There was significant difference in posterior surface elevation between pre-operation and post-operation (t=-4.033,-4.745;P=0.000,0.000) and no statistically significance between 1 month and 3 months postoperatively (t=-0.179, P=0.859). 10.The posterior corneal surface had a forward shift of (1.61±4.19)μm at lmonth and (1.74±3.67)μm at 3 months, no statistically significance (t=-0.315,P=0.754) 11.There are several factors relevant to the posterior corneal surface including diopter, ablation depth, ablation ratio, residual bed thickness (RBT) and RBT/CCT (P< 0.05).12. There was no statistically significance between posterior corneal elevation and corneal thinnest thickness or pachymetry(P>0.05).13. There was no statistically significance between posterior corneal elevation and preoperative IOP (P>0.05)Conclusions:1. The mean Zernike aberrations for the cornea and whole eye in myopia tend to become progressively smaller with increasing order.2. The posterior corneal RMS errors were much smaller than the anterior surface. The entire corneal RMS was compensated by the anterior and posterior cornea.3. Ocular Sh,cornea Sh,CF Sh。CB Sh had some relationship with radius of corneal curvature and IOP,but no relationship with corneal thickness and sex.4. Zernike terms were significantly symmetric between right and left eyes.All the characteristics of the entire eye provide theoretical bases and reference for topography-guided custom corneal ablation, implantation of IOL, and diagnosis and treatment of keratoconus and other disease.5. There was significant difference in posterior surface elevation between pre-operation and post-operation and no statistically significance between 1 month and 3 months postoperatively.6.The posterior corneal surface had a forward shift of (1.61±4.19)μm at lmonth and (1.74±3.67)μm at 3 months, no statistically significance.7. Eyes with higher diopter, more ablation depth and thinner residual bed thickness may have an increasing trend of corneal forward shift. The longer the time was, the more stable the posterior corneal surface was. |
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