Preoperative Biometry and Effective Adding Power of Multifocal IOL
This study is aimed to calculate the length of near focus or effective adding power on corneal plane according to preoperative biometry (axial length and corneal power) and intraocular lens calculation formula.
Eye models with a keratometric power ranging from 36 diopter to 48 diopter (by each 2 diopter) and an axial length ranging from 20 to 30 mm (by each 2 mm) were simulated to calculate intraocular lens power for emmetropic target. The adding power of multifocal diffractive intraocular lens was added to IOL power for emmetropic target and the near target diopter was calculated from the total IOL power. The simulation was performed by two kinds of multifocal intraocular lens those are commonly used and have the optimized intraocular lens constants from relatively more cases: Alcon Restor SN6AD1 and in Zeiss AT LISA 809M.
Effective adding power at corneal plane changes according to preoperative corneal power and axial length. As preoperative corneal power steepened, the effective adding power decreased. Similarly, as axial length lengthened, the effective adding power decreased. When the corneal power is 48.0 diopter and the axial length is longer than 24.0 mm, the effective adding power of +3.75 diopter adding multifocal IOL would be lesser than the effective adding power of +3.00 diopter adding IOL when corneal power is 36.0 diopter and axial length is 20.0 mm.
The effective adding power and the focal length on near target changes according to preoperative biometry and theoretical intraocular lens calculation formula.