Effect Of Aging And Phacoemulsification On High Order Aberrations Of Cornea

Objective:To investigate the distribution of the higher-order aberrations(HOAs, 3rd to 6th order)of anterior and posterior surface of the cornea in the population;to evaluate the symmetry of the HOAs of anterior and posterior surface of cornea between right and left eyes of individuals;and to study the variations in the HOAs of anterior and posterior surface of cornea with aging.To study the effect of phacoemulsification surgery on the optical high order aberrations(HOAs) of the cornea measured with Pentacam(Oculus,Germany).Methods:It was a prospective clinical study.HOAs of the anterior and posterior cornea were measured using Pentacam(Oculus,Germany) on 180 eyes of 90 subjects (age range 20 to 79 years;30 eyes in each decade;manifest refractive of -3.0 and +3.0 diopters(D),cylinder of＜2.0 D).HOAs include all Zernike terms,the total high order aberration(tHOA),spherical aberration(SA),coma,3^rd,4^th,5^th,6^th order aberrations.Root-mean-square(RMS) values of HOAs were obtained with 6.0mm aperture both the anterior and posterior surface of cornea.Correlation analysis was performed to investigate the aberration symmetry between the right and left eyes and to assess the association between HOAs of the anterior and posterior cornea and age.It was a prospective non-random controlled clinical study.HOAs of the anterior and posterior surface of cornea were measured before and after phacoemulsification surgery on 51 eyes of 45 patients.Monofocal foldable IOLs were implanted after phacoemulsification through a clear-cornea,3.2mm incision without suture.Patients were seen 1day before surgery,and 7 days,1 and 3 months after surgery.HOAs include the total high order aberration(tHOA),spherical aberration(SA),coma, trefoil,3^rd,4^th,5^th,6^th order aberrations.Root-mean-square(RMS) values of HOAs were obtained with 3.00mm and 6.00mm aperture using corneal topography of Pentacam pre- and postoperative,and were divided into 3.00mm and 6.00mm aperture groups.Aberrations were compared in each eye using repeated measures and the optical changes induced by surgery investigated.Results:There was wide individual variability in HOAs of the anterior surface of cornea with ranges of individual Zernike terms from -0.898 to 1.138μm.The mean coefficient of the 4^th order spherical aberration(Z₄⁰) of the anterior surface of cornea was(0.301±0.139)μm and was positive in all corneas.The mean root-mean-square(RMS) values were(0.609±0.215)μm for tHOA,(0.303±0.138)μmforSA(Z₄⁰andZ₆⁰),and(0.326±0.179)μm for Coma(Z₃^-1,Z₃¹,Z₅^-1, Z₅¹ ).Moderate to high correlations were found between right and left eyes for tHOA, SA,and coma(pearson r=0.490,0.714,0.391 respectively,all P＜0.001).RMS of tHOA and coma of the anterior surface of cornea increased with aging(Spearman,r= 0.327,0.302 respectively,both P＜0.001);SA RMS was not correlated with change in age(r=0.087,P＞0.05).There was wide individual variability in HOAs of the posterior surface of cornea with ranges of individual Zernike terms from -1.997 to 2.086μm.The mean coefficient of the 4th order spherical aberration(Z₄⁰) of the posterior surface of cornea was(0.626±0.261)μm and was not positive in all corneas.The mean root-mean-square(RMS) values were(1.496±0.502)μm for tHOA,(0.644±0.252)μm for SA(Z₄⁰ and Z₆⁰),and(0.673±0.407)μm for Coma(Z₃^-1,Z₃¹ Z₅^-1, Z₅¹).Moderate to high correlations were found between right and left eyes for tHOA, SA,and coma(pearson r=0.339,0.817,0.532 respectively,all P＜0.05).RMS of tHOA and coma of the posterior surface of cornea increased with aging(Spearman r =0.259,0.382 respectively,both P＜0.05);SA RMS was not correlated with change in age(r=0.110,P＞0.05).The total HOA of the anterior surface increased slightly from a mean of (0.289±0.171)μm preoperatively to(0.312±0.158)μm postoperatively with 3.0mm aperture,and(0.980±0.215)μm preoperatively to(1.054±0.308)μm postoperatively with 6.0mm aperture;the increase was not statistically significant(F=1.55,P=0.22), and the changing trend of the tHOA were similar between the two groups of 3.00mm and 6.00mm aperture(F=0.95,P=0.42).The changes of other HOAs were similar to the tHOA pre- and postoperative.The tHOA of the posterior surface increased significantly from(0.548±0.220)μm preoperatively to(0.661±0.275)μm postoperatively with 3.0mm aperture,and(1.780±0.453)μm preoperatively to (1.945±0.532)μm postoperatively with 6.0mm aperture;the increase was statistically significant(F=15.83,P=0.00).The changing trend of the tHOA were not similar between the two groups(F=12.46,P=0.00).The changes of other HOAs were similar to the tHOA pre- and postoperative.Conclusion:HOAs of the anterior and posterior surface of cornea waried greatly among subjects and decreased significantly with ordering.The RMS values of the HOAs of the posterior cornea were much larger than that of the anterior cornea.All Zernike terms had a normal distribution,both the anterior cornea and the posterior cornea.A moderate to high degree of symmetry existed between right and left eyes. tHOA and coma of the anterior and posterior surface of cornea were increased with aging,but SA was not changed with aging.Phacoemulsification cataract surgery does not systematically degrade the optical quality of the anterior corneal surface. However,it introduces significant changes in all HOAs of the posterior surface of cornea,so the surgery may degrade the optical quality of the posterior corneal surface.