*2.3.2 Optical biometry*

Optical biometry, which is based on monochromatic light-emitting diodes, [16] including partial coherence interferometry (PCI) [e.g. IOLMaster 500 (Carl Zeiss Meditec AG, Jena, Germany)] and swept source OCT (ss-OCT) [eg. IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany), Anterion (Heidelberg Engineering, Heidelberg, Germany)], serves as highly reliable method for AL (in mm), ACD (in mm) and keratometry (in diopters) determination. In comparison with standard keratometry, total keratometry measured with ss-OCT (IOLMaster 700) is a new measurement for the assessment of anterior and posterior corneal curvatures that seems to show higher accuracy in IOL power calculation and better refractive outcomes in eyes with or without previous laser refractive surgery [17–19]. As a result, it has been established as the most common preoperative examination performed to calculate the IOL power. According to the selected technique and patient, the postoperative refractive target is plano, low myopia or low hyperopia [20]. A variety of formulas have been used for the most accurate IOL power calculation. Since it has been found that inaccurate biometry is the most common cause of residual postoperative refractive error, [21] some factors should be taken into account; among them, interocular consistency in AL and K values, appropriate formula for each case, and outliers [22]. Last but not least, preoperatively, the surgeon should check and confirm that the biometry corresponds to the correct patient.
