HM-ZL formula

An IOL power calculation formula for highly myopic eyes-developed by Zhu and Lu

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The HM-ZL formula was a novel artificial intelligence-based formula for highly myopic eyes (axial length over 26.00 mm) developed by Zhu and Lu.


The HM-ZL formula requires compulsory information input of axial length, anterior chamber depth, lens thickness, white to white distance, flattest and steepest K values (namely the K1 and K2), A-constant, a0, a1, and a2 constants. We recommend using the constants from the ULIB website ( A default refractive index of 1.3375 has been selected. If your device uses a different refractive index, please select the appropriate option from the drop-down menu. The training dataset has updated to 31 Dec 2021; we will continue to include new data to improve the performance of the Zhu-Lu formula. If you have any questions or suggestions or want further information about the HM-ZL formula, please contact us at