Effects Of Corneal Refractive Surgery With Excimer Laser On Human Ocular Wavefront Aberrations

Wavefront aberration refers to the difference between the optimal wavefront of the optical system and the actually measured optical system wavefront. In recent years, along with the developing new technique, people have a new concept of the wavefront aberration. It had been improved that wavefront aberration had a close relationship with vision quality. To get a deeper understanding the impacts of wavefront aberration on vision quality, we designed a clinical study to compare the difference of wavefront aberration before and after the corneal refractive surgery with excimer laser for myopic and astigmatic eyes, so as to analyze the characteristic of the wavefront aberration and the factors that impact it more fully, hoping to offering the relative information for wavefront aberration supported customized ablation(WASCA)and further improving technique of the operation.Objective: 1. To study the characteristic and variation rules of the wavefront aberration before and lmonth,3 months and 6 months after keratorefractive surgery (LASIK or LASER) ; 2. To analyze the relative factors that keratorefractive surgery (LASIK or LASEK) changes the wavefront aberration.Methods: We included 86 eyes of 44 patients who intend to take corneal refractive surgery (LASIK or LASEK) from our ophthalmic refractive surgery center.The kinds of the surgery were chosen by patients themselves. We adopt the objective aberrometry (the Zywave~TM aberrometry made by BAUSCH & LOMB).It's software function can offer a large pupil examination, displaythe RMS value of total wavefront aberration and higher order aberration with 5mm pupil and the RMS value of total wavefront aberration .higher order aberration and the aberration of each order with 6mm. Wavefront aberration examinations were taken for all the patients before and 1 month, 3 months and 6 months after the surgery with excimer laser (LASIK or LASEK) . MADLAB software was used to analyze the results so as to get the 20 Zernike coefficients for quantitive analysis; Paired t test and independent t test were used for statistic analysis.Results:Pre-operation: 1. The aberrations of the refractive error patients before surgery were mainly lower order aberrations. The main higher order aberrations are coma aberration and spherical aberration. 2. Aberration did not have significant correlation with age, sex and which of the eye.3. There was a positive correlation between the aberration and the diameter of the pupil.4. The relationships between aberration and degree of myopia were: in the 0----6D low-moderate myopia patients, there was no significant correlation between higher order aberration and dioptric power. In the high myopia >-6D, there was significant positive correlation between higher order aberration and dioptric power. Among the aberrations, the coma, spherical, trefoil aberration all have correlation with the dioptric power. 5. The relationships between aberration and astigmatism degree were: in the 0~~ — 0. 75D low-moderate astigmatism patients, there was no significant correlation between higher order aberration and dioptric power. In the =￡— 0. 75D high astigmatism patients, there was significant positive correlation between higher order aberration and dioptric power. The coma and trefoil aberrations had positive correlation with astigmatism degree, but the spherical aberration did not have significant correlation with it.Post-operation: 1. Total aberrations and the lower order aberrations decreased after the surgery, while the higher order aberrations increased, especially spherical aberrations. 2. The relationships between aberration and pupil diameter after the operation were: total wavefront aberrations and higher order aberrations increase with the pupil diameter. The correlation between aberration and the pupil diameter was more obvious after the operation than before it. 3. The amount of the higher order aberration increase after surgery had positive correlation with the amount of ablation. 4. The amount of the higher order aberration increase had negative correlation with the ablation diameter. 5. The impacts of the surgery manner on the higher order aberration after the operation were: 1 and 3 months after the operation, the LASIK group had a little lower RMS value of the higher order aberration than the LASEK group, and the LASIK group had a higher RMS value than the LASEK group 6 months after the operation,but the differences did not have statwastic significance; 1,3, and 6 months after operation, the LASIK group had lower RMS values of coma and trefoil aberration than the LASEK group, but a higher RMS value of spherical aberration than the LASEK group, the differences did not have statwastic significance.Conclusions: 1. After corneal refractive surgery with excimer laser, the higher order aberration especially spherical aberration increased significantly, and this may be the cause of the vwasion quality degression. 2. The aberration increases with increasing pupil size no matter before or after operation, which accorded with the fact that the patients have daze and a worse sight at night. 3. The patients who had higher myopia and astigmatwasm degree also had a higher aberraion, thus had a related worse vwasion quality.4. The post-operation higher order aberration had a positive correlation with the ablation amount,but a negative correlation with the ablation diameter.5. After the operation, the LASEK group had a higher higher order aberrationthan the LASIK group in the early period, but vice versa 3 months after operation.