thirty - three patients ( 66 eyes ; mean age 25.515.6 years ) who underwent laser refractive surgery for myopia correction between november 2006 and may 2007 followed up for more than 3 months were retrospectively reviewed . twenty - eight patients underwent laser in situ keratomileusis ( lasik ) surgery , and 5 patients underwent photorefractive keratectomy ( prk ) surgery . all surgeries were performed using ladarvision 4000 ( alcon , usa ) by a single surgeon ( park wc ) . anterior corneal aberration and ocular aberration were measured by pentacam and an aberrometer ( ladarwave ) , respectively , before , 1 month , and 3 months after surgery , with the diameter of the measured zone set to 6.5 mm . among hoas , total hoa was calculated as a root mean square ( rms ) value between the 3 and 6 order aberrations . pentacam is a rotating schiempflug camera , which generates images from the anterior surface of the cornea to the posterior surface of the lens , and can create a corneal elevation map . pentacam can also perform zernike analysis for the anterior and posterior surface based on the measured height data up to the 8 order aberration . ladarwave is an aberrometer using the hartmann - shack sensor and measured up to the 6 order aberration in the present study . total hoa was calculated up to the 6 order aberration for comparison between pentacam and ladarwave. statistical analysis was performed using the statistical product and service solutions software 15.0 for ms windows ( spss inc , usa ) . a paired t - test was used to analyze changes of aberrations before and after surgery . correlations between the aberrations were analyzed by bivariate correlation analysis calculating the pearson correlation coefficient . anterior corneal aberrations and ocular aberrations were measured by pentacam and an aberrometer ( ladarwave ) , respectively , before , 1 month , and 3 months after surgery . internal optics aberration values , ocular aberration minus anterior corneal aberration , were also calculated . before surgery , the positive values of anterior corneal aberrations were compensated by negative values of internal optics aberrations , and complete ocular aberrations were measured low . there were no significant changes of internal optics aberrations after surgery , and aberrations of internal optics remained relatively constant ( table 1 ) . the mean preoperative value of total hoas was 0.4160.113 m , anterior corneal surface value was 0.7820.136 m , and internal optics value was -0.3660.172 m . at 1 month after surgery , anterior corneal aberration and ocular aberration increased to 1.152 m and 0.737 m , respectively , but aberration of the internal optics remained at -0.415 m , similar to the preoperative value . at 3 months after surgery , anterior corneal aberration and ocular aberration continued to increase , but the internal optics aberration remained constant . when the bivariate correlation analysis was performed to evaluate the correlation between anterior corneal aberration and internal optics aberration before surgery , the pearson correlation coefficients were -0.796 , -0.810 , and -0.752 in coma , spherical aberration , and total hoa , respectively ( p=0.000 ) ( table 2 ) . these results displayed a negative correlation between the anterior corneal aberration and internal optics aberration ( fig . 2 ) . drawing graphs pertaining to the changes of hoas before and after surgery , the anterior corneal aberration and ocular aberration were observed to increase equally , while the internal optics aberration maintained at a low level ( fig . a high value of anterior corneal aberration ( 0.648 m ) was compensated by the negative value of the internal optics aberration ( -0.496 m ) , allowing the ocular aberration ( 0.152 m ) to remain at a low level ( fig . calculating increasing rates of aberrations before and 3 months after surgery , coma , spherical aberration and total hoa increased 1.7- , 2.6- , and 1.8-fold from previous values in anterior corneal aberrations , respectively . in ocular aberrations , coma , spherical aberration , and total hoa increased by 1.5 , 1.4 , and 1.5 times that of previous values , respectively ( table 1 ) . regarding internal optics aberrations , there were no statistically significant differences before and after surgery in coma , spherical aberration , and total hoa ( all p>0.05 ) . before surgery , correlations between anterior corneal aberration and ocular aberration were not statistically significant for coma , spherical aberration , and total hoa , but became statistically significant after surgery . one month after surgery , the pearson correlation coefficient values were 0.535 , 0.662 and 0.696 ( all p=0.000 ) in coma , spherical aberration , and total hoa , respectively . three months following surgery , the correlation coefficients were 0.413 , 0.604 , and 0.734 with p - value 0.001 , 0.000 , 0.000 , respectively ( table 1 ) . anterior corneal aberrations and ocular aberrations were measured by pentacam and an aberrometer ( ladarwave ) , respectively , before , 1 month , and 3 months after surgery . internal optics aberration values , ocular aberration minus anterior corneal aberration , were also calculated . before surgery , the positive values of anterior corneal aberrations were compensated by negative values of internal optics aberrations , and complete ocular aberrations were measured low . there were no significant changes of internal optics aberrations after surgery , and aberrations of internal optics remained relatively constant ( table 1 ) . the mean preoperative value of total hoas was 0.4160.113 m , anterior corneal surface value was 0.7820.136 m , and internal optics value was -0.3660.172 m . at 1 month after surgery , anterior corneal aberration and ocular aberration increased to 1.152 m and 0.737 m , respectively , but aberration of the internal optics remained at -0.415 m , similar to the preoperative value . at 3 months after surgery , anterior corneal aberration and ocular aberration continued to increase , but the internal optics aberration remained constant . when the bivariate correlation analysis was performed to evaluate the correlation between anterior corneal aberration and internal optics aberration before surgery , the pearson correlation coefficients were -0.796 , -0.810 , and -0.752 in coma , spherical aberration , and total hoa , respectively ( p=0.000 ) ( table 2 ) . these results displayed a negative correlation between the anterior corneal aberration and internal optics aberration ( fig . drawing graphs pertaining to the changes of hoas before and after surgery , the anterior corneal aberration and ocular aberration were observed to increase equally , while the internal optics aberration maintained at a low level ( fig . a high value of anterior corneal aberration ( 0.648 m ) was compensated by the negative value of the internal optics aberration ( -0.496 m ) , allowing the ocular aberration ( 0.152 m ) to remain at a low level ( fig . similar patterns were found for coma and total hoa . calculating increasing rates of aberrations before and 3 months after surgery , coma , spherical aberration and total hoa increased 1.7- , 2.6- , and 1.8-fold from previous values in anterior corneal aberrations , respectively . in ocular aberrations , coma , spherical aberration , and total hoa increased by 1.5 , 1.4 , and 1.5 times that of previous values , respectively ( table 1 ) . regarding internal optics aberrations , there were no statistically significant differences before and after surgery in coma , spherical aberration , and total hoa ( all p>0.05 ) . before surgery , correlations between anterior corneal aberration and ocular aberration were not statistically significant for coma , spherical aberration , and total hoa , but became statistically significant after surgery . one month after surgery , the pearson correlation coefficient values were 0.535 , 0.662 and 0.696 ( all p=0.000 ) in coma , spherical aberration , and total hoa , respectively . three months following surgery , the correlation coefficients were 0.413 , 0.604 , and 0.734 with p - value 0.001 , 0.000 , 0.000 , respectively ( table 1 ) . aberration is the difference between a real image and an ideal image occurring when plane wavefront is refracted by snell 's law . ideally , parallel light focuses on one point . however , the eye is not a perfect circle for focusing incoming light on one point , and eventually an aberration occurs . zernike analysis is commonly used in ophthalmology to express ocular wavefront error in the form of a polynomial equation . specifically , the zernike polynomial describes the shape contribution made by a series of sine and cosine basis functions to the total wavefront error surface . the rms is a measure of the magnitude of the wave aberration.11,12 increased hoa after laser refractive surgery causes complications such as a decrease in contrast sensitivity , halos , glare , starbursts , and ghost images , which degrade visual quality.4 - 8 mccormick et al . verified the mean hoa of patients complaining of complications increased 2.26-fold higher than that of patients without problems.8 ocular aberration is composed of an anterior corneal aberration and internal optics aberration . in principle , internal optics aberration should be measured directly , but direct measurement is difficult in all patients . compared directly measured internal optics aberrations after neutralizing anterior corneal aberrations by water - filled goggles and indirectly calculated internal optics aberrations by subtracting anterior corneal aberrations from ocular aberrations . the result showed that directly and indirectly measured values of internal optics aberrations were the same.9 based on this study , internal optics aberration was defined in the present study as ocular aberration minus anterior corneal aberration , which were measured by ladarwave and pentacam , respectively . the compensating effect of internal optics aberration for anterior corneal aberration contributes to acquisition of a fine image.9,10 in this study , a negative correlation between the anterior corneal aberration and internal optics aberration before surgery was identified ( table 2 ) . additionally , results confirmed that the positive values of anterior corneal aberrations were compensated by negative values of internal optics aberrations , and complete ocular aberrations were maintained at a low level before surgery . an increase in aberration after conventional refractive surgery has been confirmed by numerous studies.7,13,14 however , studies regarding aberration changes after customized refractive surgery have produced varying results . an increase in aberrations but lower increasing rates than conventional refractive surgery15 - 18 , no significant increase19 , or even a decrease in aberrations20 than the preoperative state has been reported . in this study , anterior corneal aberrations were increased , but internal optics aberrations were not influenced by surgery and remained constant . as a result , ocular aberration increased to the same degree as the anterior corneal aberration increased . graphs pertaining to changes of hoas before and after surgery also showed that the anterior corneal aberration slope and the ocular aberration slope increased at same rate , while internal optics aberration maintained a low level ( fig . 3 ) . calculating increasing rates of aberrations before and 3 months after surgery , coma , spherical aberration and total hoa increased by 1.7- , 2.6- , and 1.8-fold from previous values in anterior corneal aberrations and 1.5- , 1.4- , and 1.5-fold from previous values in ocular aberrations , respectively ( table 1 ) . regarding internal optics aberrations , there were no statistically significant changes in coma , spherical aberration and total hoa before and after surgery ( all p>0.05 ) . correlations between anterior corneal aberration and ocular aberration were not significant in coma , spherical aberration , and total hoa before surgery , but became statistically significant in all aberrations after surgery ( table 1 ) . this can be explained by the increase of anterior corneal aberration after surgery which exceeds the limit of the compensating effect of internal optics aberration . this alteration is believed to result in a larger proportion of anterior corneal aberration in ocular aberrations and to induce changes of correlation between anterior corneal aberration and ocular aberration . patients in the current study were followed up for 3 months after surgery , but more time was necessary to observe complete changes in hoa . additionally , various methods of surgery were included in this study , but there were not enough cases to identify any differences among these methods . the authors are planning to study the differences of aberrations depending on laser refractive surgery methods by including more cases and a longer follow - up period . an increase of hoa after refractive surgery could degrade the quality of vision , and thus accurate analysis of the aberrations and techniques to lower hoa is imperative to improve visual quality .
purposeto compare changes of anterior corneal aberration ( pentacam ) and ocular aberration ( aberrometer , ladarwave ) after laser refractive surgery.methodssixty-six eyes underwent laser refractive surgery and were retrospectively reviewed . 
 anterior corneal aberration and ocular aberration were measured by pentacam and an aberrometer ( ladarwave ) respectively . 
 changes of root mean square ( rms ) values of coma , spherical aberration , and total high order aberration ( hoa ) were evaluated before , 1 month , and 3 months after surgeryresultsocular aberrations displayed low preoperative values , but after laser refractive surgery , anterior corneal aberration and ocular aberration increased equally . 
 there were no statistically significant differences of internal optics aberration values ( ocular aberration minus anterior corneal aberration ) in coma , spherical aberration , and total hoa . 
 anterior corneal aberration and ocular aberration showed statistically significant correlations at 1 and 3 months after surgery.conclusionsinternal optics aberration compensated the anterior corneal aberration effectively before surgery , but the increase of anterior corneal aberration after laser refractive surgery exceeded the compensation of internal optics . as a result , anterior corneal aberration and ocular aberration increased equally . 
 the correlation between anterior corneal aberration and ocular aberration after surgery was statistically significant due to the increased proportion of anterior corneal aberration in ocular aberration .