Accuracy of intraocular lens power calculation in high myopia

To study the accuracy of different recent intraocular lens (IOL) calculation formulas in predicting a target postoperative refraction ± 1.0D (Diopters) in patients with long eyes (axial length ≥ 26.0 mm) undergoing phacoemulsification.

This study comprised 127 eyes of 87 patients who presented with cataract and axial eye length ≥ 26 mm. Before phacoemulsification and IOL implantation; axial length measurement using immersion ultrasound A-scan technique, and autokeratometry with or without computerized corneal topography for K readings were done. The IOL power was calculated using four formulas, namely the SRK-T, Hoffer-Q, Holladay-2, and Haigis formulas. Four months after surgery, refraction was done. Differences between actual postoperative refraction and assumed target refraction using the different formulas were analyzed. P < 0.05 was considered statistically significant.

In all 127 eyes, the mean axial length was 31.71 mm (range, 26.06-37.11 mm) and the mean K was 44.68 D (range, 40.05-55.14D). The mean preoperative spherical equivalent (SE) was -17.52D (range, -12.25 to -30.50D). After surgery, the mean spherical equivalent was -0.8 ± 0.83D (range, +1.25 to -3.75D). The mean postoperative refractive SE when implanting a plus power IOLs was -0.3 ± 0.51D (P < 0.001) while the mean postoperative refractive SE when implanting a minus power IOLs was +1.21 ± 0.11D denoting a highly significant tendency toward hyperopia (P < 0.001). Concerning the minus power group, most postoperative refractive error was within +1.0 to +2.0D in the actual implanted IOL and in all other formula calculated IOL power. However, Haigis formula showed the least deviation while SRK-T and other formulas showed a greater tendency toward hyperopia.

In eyes with high axial myopia, the performance of SRK-T, Hoffer-Q, Holladay-2 and Haigis formulas are comparable in low plus-powered IOL implantation. Haigis formula is the best formula when minus power IOL is implanted.