Refraction after Cataract Surgery Depending on Intraocular Lens Calculation Formula

Abstract

Introduction. Prospective study was made to evaluate and compare predictability and accuracy of three IOL power calculation formulas (SRK/T, SRK II and Haigis) for IOL power calculation.

The postoperative refractive expectations of patients having cataract surgery have been increased due to the advances in technology. Therefore, accurate intraocular lens (IOL) power calculation is very important to attain the postoperative target refraction. (6) Results between each formula could not differ, but frequently there are patients with a radical difference in calculations.

Aim of the study.The aim of this research was to analyze predictability and accuracy for IOL power calculation, evaluate and compare estimation error of three IOL power calculation formulas (SRK/T, SRK II and Haigis).

Material and methods. Prospective study included 25 eyes of 25 patients who underwent phacoemulsification with IOL implantation. Postoperative refraction and refraction predicted by the SRK II, SRK/T and Haigis formulas were analyzed. The mean estimation error (EE), mean absolute estimation error (AEE) and the percentage of eyes within target refraction (EWTR) (± 0.50 D and ± 1.00 D) for all three formulas were compared. Analysis was repeated in three groups with three subgroups in each group. These groups formed based on axial length (AL) (group 1.1: < 23 mm, group 1.2: 23 - 24 mm, group 1.3: > 24 mm), keratometry (K value) (group 2.1: < 43 D, group 2.2: 43 - 45 D, group 2.3: > 45 D) and anterior chamber depth (ACD) (group 3.1: < 3 mm, group 3.2: 3 - 3.5 mm, group 3.3: > 3.5 mm).

Results. In the overall study group, the smallest mean AEE (0.33 ± 0.17) was provided by the SRK/T formula. The highest percentage of EWTR ± 0.50 D and ± 1.00 D was also found by using SRK/T (80% and 100%).

SRK/T provided the smallest mean AEE (0.55 ± 0.25 and 0.26 ± 0.18) for groups 1.1 (n = 8) and 1.3 (n = 7), however, there was no statistically significant difference between all three formulas in group 1.3 (P = 0.22). In group 1.2 (n = 10), the smallest mean AEE (0.37 ± 0.26) was obtained using SRK II.

Haigis provided the smallest mean AEE (0.31 ± 0.09) in group 2.1 (n = 4). In both, group 2.2 (n = 11) and 2.3 (n = 10) the smallest mean AEE was found by using SRK/T (0.43 ± 0.18) and 0.21 ± 0.09).

In all subgroups of group 3 (group 3.1 (n = 4), group 3.2 (n = 14) and group 3.3 (n = 7), SRK/T showed the smallest mean AEE (0.26 ± 0.12), (0.40 ± 0.19) and (0.23 ± 0.09), however, no significant difference was found between all three formulas (P = 0.17, P = 0.24 and P = 0.31)

SRK/T provided the highest percentage of EWTR ±0.50D and ±1.00D in all subgroups, except 2.2, where Haigis showed better percentage of EWTR ±0.50D. (54% < 63%)

Conclusions. Better results can be obtained using SRK/T formula in almost every eye, except SRK II formula may be preferred in eyes with moderate AL and Haigis formula in eyes with K value under 43D.