Discussion On The Accuracy Of IOL Calculation Method After Myopia Corneal Laser Correction

Objective:To compare the accuracy of Barrett True-K formula,Haigis-L formula and Shammas-PL formula in the calculation of intraocular lens after laser correction of corneal myopia,and to explore the relationship between them and axial length.Methods:Retrospective clinical study.21patients（25 eyes in total）who underwent corneal myopia laser correction surgery in the Second Hospital of Jilin University from November 2019 to December 2021 were selected and divided into group A（AL≤26mm）,group B（26mm28mm）according to the axial length of eyes.Relevant parameters were measured by IOLMaster 700 and AL-Scan for each patient before surgery,the IOL model and degree were selected according to the operator’s experience and patient’s needs,so that the reserved degree of the three calculation formulas could be obtained respectively.All patients underwent phacoemulsification with intraocular lens implantation,and optometry was performed3 months after the operation to obtain the actual equivalent diopter.The difference between the actual and reserved degrees was calculated to compare the accuracy of the three calculation formulas and explore the relationship between them and eye axis.Results:1、For all eyes,the average prediction errors of Barrett True-K formula,Haigis-L formula and Shammas-PL formula were-0.89±0.96 D,-1.35±0.90 D and-0.98±1.10 D,respectively.The average absolute refractive errors were 1.04±0.78 D,1.39±0.84 D and1.20±0.85 D,respectively,which were significantly different from 0（P<0.01）.Although there was no significant difference among the three（P>0.05）,the error value of Barrett True-K formula was the minimum.The absolute refractive errors of Barrett True-K formula,Haigis-L formula and Shammas-PL formula were 28%,20%and24%respectively in the range of 0.5D,and there was no statistically significant difference in the proportions of each formula.In the range of 0.75 D,the proportion of Barrett TrueK was 48%,32% and 28%,and the proportion of Barrett True-K was higher than that of the other two formulas（P<0.05）.In the 1.0D range,the proportions of 0.75 D and1.0D were 56%,40% and 44%,respectively,and there was no statistical significance in the proportions of each formula（P>0.05）.2、In group A,the mean absolute errors of the three formulas were different from0（P<0.01）,and there was no statistical significance among the three groups（P>0.05）,but the error value of Haigis-L formula（1.10±0.84D）was the smallest.In group B,the mean absolute error of the three formulas was significantly different from 0（P<0.01）,and the error of Haigis-L formula was different from that of the other two formulas（P<0.05）,and the error of Barrett True-K formula was the least（0.64±0.46D）.In group C,the mean absolute error of Barrett True-K formula was significantly different from 0（P<0.01）,and there was no significant difference between the three groups（P>0.05）,but the error value of Barrett True-K formula was the smallest（1.35±0.92D）.3、For Barrett True-K formula,MAE in group B was greater than that in group C（P<0.05）,and AE≤1.0D distribution in group B was greater than that in the other two groups（P<0.05）.For Haigis-L formula,MAE had no difference among all groups（P>0.05）,and the proportion of AE≤1.0D in group A>group B>group C（P<0.05）;For Shammas-PL formula,MAE in group B was smaller than that in group A（P<0.05）,and AE≤1.0D accounted for group B>group C>Group A（P<0.05）.Unary linear regression analysis showed that the absolute error of Haigis-L formula was positively correlated with axial length（P<0.05）.When AL increased by1 mm,AE increased by 0.17D（B=0.17,P=0.013）.There was no significant correlation between the errors of the other two formulas and the axial length（P>0.05）.Conclusion:There are differences in the accuracy of the three IOL calculation formulas for patients with corneal myopia after laser correction.For patients with different eye axes,different calculation formulas can be selected: When AL≤26mmm,Haigis-L formula has higher accuracy,but when AL>26mm,Barrett True-K formula is more reliable.The accuracy of Haigis-L formula was correlated with the length of ocular axis.