Objective: To re-examine relative accuracy of intraocular lens (IOL) power calculation of immersion ultrasound biometry (IUB) and partial coherence interferometry (PCI) based on a new approach that limits its interest on the cases in which the IUB’s IOL and PCI’s IOL assignments disagree.

Material and Method: Prospective observational study of 108 eyes that underwent cataract surgeries at Taksin Hospital. Two halves of the randomly chosen sample eyes were implanted with the IUB- and PCI-assigned lens. Postoperative refractive errors were measured in the fifth week. More accurate calculation was based on significantly smaller mean absolute errors (MAEs) and root mean squared errors (RMSEs) away from emmetropia. The distributions of the errors were examined to ensure that the higher accuracy was significant clinically as well.

Results: The (MAEs, RMSEs) were smaller for PCI of (0.5106 diopter (D), 0.6037D) than for IUB of (0.7000D, 0.8062D). The higher accuracy was principally contributed from negative errors, i.e., myopia. The MAEs and RMSEs for (IUB, PCI)’s negative errors were (0.7955D, 0.5185D) and (0.8562D, 0.5853D). Their differences were significant. The 72.34% of PCI errors fell within a clinically accepted range of ±0.50D, whereas 50% of IUB errors did.

Conclusion: PCI’s higher accuracy was significant statistically and clinically, meaning that lens implantation based on PCI’s assignments could improve postoperative outcomes over those based on IUB’s assignments.

Keywords: Biometry, Intraocular lens power calculation, Ocular refraction