| Background:The accuracy of intraocular lens(IOL)power calculation in cataract patients with high myopia(axial length≥27 mm)is limited.It may affect the satisfaction of the patients to obtain a target postoperative refractive status.It is a challenge in our clinical work.There are many influence factors in IOL power calculation,such as measurement accuracy of ocular biological parameters,the selected formula for IOL power calculation,and so on.With the development of medical biotechnology,the accuracy of ocular measurement becomes higher and higher,the formula of IOL calculation has been the most important factor.With the third generation formulas,the accuracy of IOL calculation has been improved.However,in myopic eyes with axial lengths of 27.0 mm or more,the accuracy is still facing some problems.Basing on the advanced technology of measurement,the clinical data of the patients with extreme high myopia were analyzed by retrospective study,in order to obtain the methods to make the formula of IOL calculation ideal,and to get a satisfactory postoperative refractive status.Objective:To evaluate the accuracy of IOL power calculation using IOL Master and four different IOL calculation formulas(SRK-II,SRK-T,Holladay and Haigis)in myopic eyes with axial lengths of 27.0 mm or more,and to obtain the methods to optimize IOL calculation.To determine the factors that influences the accuracy of IOL calculation,and to obtain the multivariate regression equations of predictive error.To verify the accuracy of the adjust PE for SRK-T formula.Methods:Part 1: to compare the accuracy of four kinds of IOL formulas in myopic eyes.This retrospective study reviewed 105 patients(148 eyes)with high myopia and axial lengths of 27.0 mm or more,who had cataract surgery in our hospital.The power of implanted IOL and predicted postoperative spherical equivalence(PPSE)were calculated by IOL Master and four IOL power calculation formulas: SRK II、SRK-T、Holladay and Haigis.The cases were divided into different groups according to axial length.With 1 mm adding in axial length between 27.0 mm and 34 mm,each group was set.About three months after operation,the actual postoperative spherical equivalence(APSE)was calculated for each patient.The difference between APSE and PPSE from four formulas was the predictive error(PE).The PEs was analyzed by comparing the difference among four kinds of formulas in different axial length range.The axial length groups with no statistical differences of PE were combined,and the PE in each axial length range was calculated,which is named as PE1.Part 2: to analysis the factors that influence the accuracy of IOL calculation in high myopia.By using the statistical analysis software SPSS 17.0,the cases in the first part were analyzed retrospectively.In 105 cases(148 eyes),the correlations between PE and the parameters such as axial length(AL),keratometry(K1,K2),anterior chamber depth(ACD),IOL A constant,patients’ age,gender,sides of eye were analyzed and determined.The scatterplots were made,multiple linear regression analysis was entered gradually,and finally four multiple linear regression equations about PE and related factors were set up.The adjusted PE obtained from the multiple linear regression equations were named as PE2.Part 3: to verify the accuracy of the adjust PE(PE1)for SRK-T formula.In 142 cases of cataract with high myopia(axial length≥27mm),SRK-T formula was used and PE1 was used to adjust PPSE.IOL power was determined by APPSE.The difference between target spherical equivalence(TSE)and APSE was calculated and analyzed.Results:Part 1:The mean axial length of 148 eyes was(31.06±2.32)mm.PEs calculated with SRKII,SRK-T,Holladay and Haigis formulas were(1.01±1.530)D,(0.76±0.96)D,(1.24±0.8)D,and(0.78±0.84)D,respectively.Statistical differences were showed between APSE and PPSE with four IOL calculation formulas(all P<0.05).Calculating with SRK-T and Haigis formulas,there were no statistical difference between PEs(P >0.05).Calculating with Holladay formula,PE was the biggest in four formulas,and statistical differences were found among Holladay,SRK-T,and Haigis formulas(all P<0.05).The axial length groups were combined and reformed four axial intervals: 27-30 mm,30-32 mm,32-34 mm,and longer than 34 mm.Calculating with SRK-T/ Haigis formulas in these axial intervals,PEs were(0.21±0.65)D/(0.48±0.71)D,(0.58±0.56)D/(0.58±0.61)D,(1.18±0.67)D/(0.97±0.61)D,and(1.97±1.44)D/(1.76±1.26)D.The predictive errors(PE1)of SRK-T formula in four different axial intervals were: 0.2 D in 27-30 mm group,0.6 D in 30-32 mm group,1.2 D in 32-34 mm group,and 2.0 D in ≥34mm group.Part 2:By single factor linear correlation analysis,there were linear correlation between PEs and AL,K1,and K2,but no linear correlation between PEs and IOL A constant,age,gender and sides of eye.The multiple regression equation models about PEs and related factors were:SRK-II:Y=-7.871+0.538×AL-0.177×KSRK-T:Y=-12.597+0.241×AL+0.130×K2Holladay:Y=-9.691+0.155×AL+0.136×K2Haigis:Y=-11.340+0.158×K2 +0.161×ALPart 3:The average diopters of TSE,APSE,PPSE and APPSE1 obtained by SRK-T formula and PE1 were: TSE(-2.36±1.10)D,APSE(-2.37±1.26)D,PPSE(-2.44±1.01)D,and APPSE1(-3.15±1.09)D.There were no statistically significant difference between TSE and APSE,between TSE and PPSE,and between PPSE and APSE(P>0.05).There were no differences between TSEs and APSEs in 30-32 mm group,32-34 mm group,and≥34mm group(P>0.05),but there was significant difference in 27-30 mm group(P <0.05).Further analysis could be the significant difference in 29 mm group(t = 12.765,P = 0.011).Conclusions:In eyes with axial lengths of 27.0 mm or more,the accuracy of IOL calculation with SRK–T and Haigis formulas is relatively high,but calculation with the four formulas there are significant differences between PPSE and APSE.Axial length and keratometry are the main factors influencing the accuracy of IOL calculation.By adjusting PPSE with PE1 in IOL calculation with SRK-T formula,we could obtain the accurate postoperative refractive status. |
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