Evaluation of Orbscan II plus non-history double-K method in intraocular lens power calculation for patients after refractive surgery

Abstract

To explore the accuracy of intraocular lens (IOL) power calculation with non-history method using the keratometric value derived from one zone of Orbscan II topography after laser in situ keratomileusis (LASIK). For this retrospective study, 20 eyes from 20 patients undergoing myopic LASIK were included from August 2008 to November 2011. Posterior corneal curvature in peripheral 7 to 10 mm fitting zone of postoperative cornea was measured with Orbscan II topography. The ratio between anterior cornea and posterior cornea was used to calculate the preoperative total corneal power of each eye. The predicted postoperative spherical equivalent was calculated by the calculated preoperative total corneal power, power of implanted IOL, refractive error before cataract surgery and eye length from IOL-Master into the double-K method for SRK-T formula. The predicted postoperative spherical equivalent was also calculated by double-K method for SRK-T formula with clinical history. The mean difference between actual and predicted postoperative spherical equivalent, i.e. mean absolute error (MAE), were compared. (1) Non-history method: MAE of 11 eyes was within ± 0.5 D (55%), MAE of 15 eyes within ± 1.0 D (75%) and MAE of all eyes within ± 2.0 D. (2) Clinical-history method: MAE of 10 eyes was within ± 0.5 D (50%), MAE of 14 eyes within ± 1.0 D (70%) and MAE of all eyes within ± 2.0 D. (3) Comparison of non-history and clinical-history methods: The MAE of non-history method was (0.61 ± 0.59) D and the MAE of clinical-history method (0.68 ± 0.55) D. Paired t-test showed no statistically significant difference between two methods (t = -1.248, P = 0.227). The non-history method using the keratometric value derived from one zone of Orbscan II topography after LASIK provides an accurate calculation of IOL power and it can be used as a substitute for incomplete clinical data.