Accuracy of the O Formula Based on OCT and Ray-Tracing for Intraocular Lens Power Prediction
Yosai Mori1, So Goto2, Naoyuki Maeda3
1From the Miyata Eye Hospital (Y.M., K.M.), Miyakonojo, Miyazaki, Japan.
American Journal of Ophthalmology
|August 27, 2025
Summary
The O formula shows high refractive accuracy for intraocular lens (IOL) power calculation, outperforming several current methods without needing A-constant optimization. This makes it a reliable option for cataract surgery outcomes.
Area of Science:
- Ophthalmology
- Biomedical Engineering
- Optical Metrology
Background:
- Intraocular lens (IOL) power calculation is crucial for achieving desired refractive outcomes after cataract surgery.
- Existing formulas vary in accuracy, necessitating continuous evaluation and development of new predictive models.
- The ray-tracing method offers a sophisticated approach to optical modeling for IOL calculations.
Purpose of the Study:
- To assess the predictive accuracy of the O formula, a novel ray-tracing-based method.
- To compare the O formula's performance against established IOL power calculation formulas available on the ESCRS website.
- To evaluate the O formula's utility as a reliable tool in routine cataract surgery.
Main Methods:
- A retrospective analysis of 325 eyes from consecutive patients undergoing cataract surgery with acrylic IOLs.
- Comparison of the O formula with Barrett Universal II (BUII), Emmetropia Verifying Optical 2.0 (EVO), Kane, Pearl-DGS, and SRK/T formulas.
- Utilized swept-source optical coherence tomography (SS-OCT) for biometry and anterior segment measurements, with manifest refraction assessed postoperatively.
Main Results:
- The O formula achieved the lowest root-mean-square absolute error (RMSAE) of 0.396 D.
- Significantly lower mean absolute error was observed with the O formula compared to BUII, EVO, Kane, and Pearl-DGS.
- The O formula resulted in a higher percentage of eyes within ±0.50 D (78.7%) and ±1.00 D compared to Pearl-DGS.
Conclusions:
- The O formula demonstrates superior refractive accuracy in IOL power calculation.
- It performs favorably against widely used formulas, even without A-constant optimization.
- The O formula is a robust, fail-safe option, less prone to significant prediction errors (>1.0 D).
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