Preoperative Biometry and Effective Adding Power of the Multifocal Intraocular Lens

Abstract

Purpose: To calculate the length of near focus or effective adding power on the corneal plane after implantation of a diffractive multifocal intraocular lens (IOL).Methods: The study was designed as theoretical study. After eye models with corneal powers ranging from 36 to 48 diopter (with intervals of 2 diopter) and axial lengths ranging from 20 to 30 mm (with intervals of 2 mm) were simulated to calculate IOL power for an emmetropic target, the adding power of a multifocal IOL was added to the IOL power and the near target diopter was calculated from the total IOL power. The simulation was performed using three types of multifocal IOLs: the AMO TECNIS ZMB00, ZLB00, and ZKB00 (+4.00 diopter, +3.25 diopter, and +2.75 diopter of adding powers at the IOL plane).Results: As the preoperative corneal power or axial length increased, the effective adding power decreased. When the shape of the cornea was abnormally steep, the effective adding power was lowest when the SRK/T formula was used, followed in ascending order by the Holladay 1 and Hoffer Q formulas. As the cornea became flatter, the effective adding power was the lowest when the Hoffer Q formula was used, followed by the Holladay 1 and SRK/T formulas.Conclusions: The effective adding power and focal length on the near target changes according to preoperative biometry and the formula used for theoretical IOL calculation.