Preliminary demonstration of a novel IOL power calculation: The O formula.

PURPOSE: To evaluate the performance of a novel formula of intraocular lens (IOL) power calculation (O formula) based on ray-tracing without commonly used parameters including ultrasound compatible axial length, keratometry readings, and A constant.

SETTING: Tokyo Medical Center, Tokyo, Japan.

DESIGN: Retrospective consecutive case series.

METHODS: A total of 423 eyes (423 subjects) implanted with a single-piece, L-loop, acrylic IOL were enrolled. All biometric data for the O formula were obtained by anterior segment swept-source optical coherence tomography (SS-OCT) and SS-OCT-based biometer. The performance of the O formula was compared with those of the Barrett Universal II (BUII) and Kane formulas at 1 month postoperatively. Statistical analysis was applied according to a heteroscedastic test with standard deviation (SD) of prediction errors as the main parameter for formula performance.

RESULTS: The SD of the O formula (0.426) was significantly lower than that of the BUII (0.464, P = 0.034) but not significantly different from the Kane formula (0.433, P = .601). The percentages of patients with refractive prediction errors within ±0.50 and ±1.00 D of the O, BUII, and Kane formulas were 75.4 and 98.6%, 77.1 and 97.9%, and 76.6 and 98.1%, respectively.

CONCLUSIONS: The O formula, based on ray-tracing using SS-OCT-based devices, is one of the promising approaches for IOL power calculation, although additional larger-scale studies are needed. It may be used as an alternative in IOL power calculation because of its independence from commonly used parameters.