Distribution Of Astigmatism On The Posterior Surface Of Cornea In Middle-aged And Elderly Population And Its Influence On The Calculation Of Astigmatism Corrected IOL

Objective:To characterize the distribution of posterior corneal surface astigmatism(PCA)in a population with age-related cataract and to assess the impact of applying two calculation methods to the calculation of astigmatism-correcting IOL(Toric IOL)Methods:Patients with age-related cataract who underwent Pentacam corneal topography examination at the Eye Hospital of Nanchang University from May 2021 to October2022 were selected from 1097 eyes(545 eyes in the right eye and 552 eyes in the left eye),with a mean age of 63.56 years(40-100 years),561 eyes in men and 536 eyes in women.There were five groups,group A: 40-49 years old(164 eyes),group B: 50-59 years old(166 eyes),group C: 60-69 years old(241 eyes),group D: 70-79 years old(248 eyes),and group E: ≥80 years old(278 eyes).The distribution pattern of astigmatism on the posterior surface of the cornea and the axial position in each age group was analyzed.Pearson correlation analysis was used to analyze the correlation between the PCA degree and age,CCT,WTW,ACA,and TCA degree,and the correlation between PCA axis position and age.Three hundred subjects eligible for Toric IOL implantation were included in the calculation of astigmatism-correcting IOLs,and their ACA as well as TCA were analyzed vectorially,and differences between the two groups were tested by paired-samples t-test,and differences within the two groups were analyzed by one-way ANOVA.Differences in Toric IOL type and axial position calculated using Method I and Method II,respectively,were evaluated.Results:1.The mean posterior corneal surface astigmatism was(0.27±0.17)D,of which82.3%(903 eyes)had retrograde astigmatism on the posterior corneal surface.PCA was negatively correlated with age(P<0.05)and positively correlated with central corneal thickness,ACA degree and TCA degree(P<0.05),and PCA axis was positively correlated with age(P<0.05).2.In the analysis of 300 subjects included in the Toric IOL calculation for ACA as well as TCA,the differences in astigmatism and KP(0)after vector analysis were statistically significant(P < 0.05)when compared between the two groups.The differences in astigmatism and KP(0)in the ACA group and KP(0)in the TCA group were statistically significant when compared within the two groups(P < 0.05).3.The residual astigmatism and the axial position of residual astigmatism were analyzed in 86 eyes before and after the Toric IOL calculation,and the differences were statistically significant(P < 0.05)when comparing the residual astigmatism,axial position,and KP(45)after vector analysis for Method I and Method II.4.In 86 eyes(28.7%),the type of Toric IOL was changed and in 214 eyes(71.3%),the type of Toric IOL was not changed.Conclusions:Posterior corneal surface astigmatism is mostly retrogressive,with a tendency for PCA to shift from retrogressive to cisgraphic astigmatism with increasing age.For middle-aged patients,PCA decreases total corneal astigmatism,and for older patients,PCA increases total corneal astigmatism.Ignoring PCA can lead to errors in the selection of the Toric IOL model and axis for some patients.The PCA as well as the TCA should be measured prior to implantation of the Toric IOL,and the Toric IOL model should be adjusted appropriately for patients for whom PCA or TCA cannot be measured.