The analysis of refractive error of long axial high myopic eyes after IOL implantation

Abstract

To investigate the factors that influence the postoperative refractive error in long axial high myopic eyes, and to compare the accuracy of optimized Haigis and SRK/T formulas. Retrospective study. From May 2008 to December 2010, 137 high myopic eyes (with axial length (AL) greater than or equal to 26 mm) of 137 patients, who got cataract surgeries at Eye Hospital of Wenzhou Medical University, were enrolled for this study. The AL, corneal curvature (K), and anterior chamber depth (ACD) were measured by IOL-Master preoperatively. The intraocular lens (IOL) power was determined by optimized Haigis and SRK/T formulas, respectively. The preoperative and postoperative refractions were measured with phoropter. The target refraction after monofocal foldable IOL implantation was between -1.96 D to -7.39 D depending on the optimized Haigis formula. The mean absolute error (MAE) equals to the absolute difference between the target refraction and the 3 months postoperative actual refraction. One-way both groups, which the AL groups were as follow: 26 mm≤AL≤28 mm, 28 mm<AL≤30 mm, 30 m<AL≤32 mm, 32 mm<AL≤34 mm and K was grouped into 40.00-42.00 D, 42.01-44.00 D, 44.01-46.00 D and 46.01-48.00 D. Linear correlation, P-P figure of normal distribution test Bland-Altman plot and linear regression were used to compare the accuracy of two IOL power formulas and analyze the correlation between the 3 months postoperative refractive error and the parameters obtained preoperatively. (1) The IOL power is related to AL, K, ACD and preoperative spherical equivalent, the regression formulas is P=118.966-1.860AL-1.255K (F=472.86, P=0.00). (2) In AL groups: No statistical difference of MAE was found between each pair of groups by optimized Haigis (F=2.73, P=0.06). However, MAE difference were found between group 26 mm≤AL≤28 mm (-0.05±1.04) D and group 30 mm<AL≤32 mm (0.94±1.21) D, group 32 mm<AL≤34 mm (0.84±0.86) D by SRK/T formula (t=-0.99, P=0.00; t=-0.89, P=0.001). In K groups: There was no statistical MAE difference by optimized Haigis or SRK/T formula between each pair of groups (F=0.32, P=0.81; F=0.56, P=0.65). (3) The limits of agreement (mean difference±1.96 SD) of refraction difference between two formulas was (-1.6,1.0) D. The preoperative predicted refraction by the two formulas and the 3 months postoperative refractive error showed linear relationship (F=9.35, P=0.00; F=7.85, P=0.00). AL was the main factor affecting refractive error after long-axial high myopic eye cataract surgery, followed by K. For preoperative prediction, SRK/T formula and optimized Haigis formula show no difference. In AL subgroups, optimized Haigis formula showed no significant difference in accuracy, comparing with SRK/T formula induced less refractive error in 26-28 mm group than in 30-34 mm group. There was no significant difference between SRK/T formula and optimized Haigis formulas in the K subgroups.