IOL Power Calculation in Long Eye

Inaccurate measurement of preoperative axial length is the main reason for postoperative refractive error in axial high myopia. When axial length is measured by optical biometry, the adoption of the original formula to transform the optical path length into a geometrical path length leads to overestimation of axial length in myopic eyes. The group refractive index adopted to calibrate optical biometry and immersion ultrasound biometry, in fact, does not take the different relative lengths of the ocular segments into account. Segmented axial length, which is obtained by adding the individual geometrical path length of cornea, aqueous depth, lens thickness, and vitreous chamber depth, provides more accurate axial length measurements in long eyes. Axial length adjustment methods (Wang-Koch adjustment) have been developed and refined to improve the refractive outcome of traditional formulas (Holladay 1, Holladay 2 and SRK/T). Similar adjustments are included in newer formulas and lead to better results compared to the original axial length measurements.