Accuracy of intraocular lens power calculation in high myopia

ABSTRACT

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