Using equivalent keratometric readings in calculating the optical power of a multifocal intraocular lens

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BACKGROUND: Modern keratotopography allows calculating Equivalent Keratometer Readings (EKR), which take additionally into account in keratometry the radius of curvature of corneal posterior surface, and this could lead to more accurate calculation of the spherical equivalent (SE) of the intraocular lens. AIM: The aim of this study is to determine the accuracy of calculating the SE of multifocal intraocular lens according to EKR data, depending on the formula used and the corneal zone. MATERIALS AND METHOD: The study included 78 patients who underwent femtolaser-assisted phacoemulsification, multifocal intraocular lens implantation and achievement of the target refraction at different distances. Retrospective calculation of the optical power of the intraocular lens was performed using biometric data from OA-2000 and EKR (zones from 0.5 to 5 mm in increments of 0.5 mm) using 10 formulas (SRK/T, Holladay 1, Holladay 2, Haigis, Hoffer Q, Barrett 2 Universal, Olsen, Kane, EVO, Hill RBF). For each combination of keratometry zone/formula were calculated: mean error of predicted refraction (ME), its difference from zero, and after intraocular lens constant optimization — mean (MAE) and median (MedAE) absolute errors, standard deviation (SD). RESULTS: Up to the 2.5 mm zone, ME is shifted towards hypermetropia, and from the 3 mm zone, ME begins to shift towards myopia according to all formulas. Minimal MAE, MedAE and SD values were detected in peripheral corneal zones (3–5 mm) for most formulas. The best indicators were demonstrated by the formula Haigis in zones 3.5–5 mm. CONCLUSIONS: The most accurate calculation of the SE of a multifocal intraocular lens using EKR is possible when using the Haigis formula in 3.5–5 mm zones.