A New Intraocular Lens Power Calculation Formula for Eyes Undergoing Lens Exchange

To introduce a new formula (manifest refraction [MR] biometry formula) for calculating intraocular lens (IOL) power when performing IOL exchange and to compare its refractive prediction accuracy with that of the Barrett Rx formula.

Retrospective case series.

Patients with eyes who underwent IOL exchange without a history of corneal refractive surgery between January 2011 and June 2025.

Intraocular lens power calculations were performed using 2 methods: (1) the MR biometry formula, which incorporates data from the original IOL (model and power), pre-exchange biometry, and MR with the original IOL; and (2) the Barrett Rx formula. Subgroup analyses were conducted based on the final IOL position: IOL fully in the capsular bag, haptics in the bag with anterior optic capture, or haptics in the ciliary sulcus with posterior optic capture. Refractive prediction errors, defined as the spherical equivalent of the actual postoperative MR minus the predicted refraction, were calculated.

Root mean square absolute errors (RMSAEs) and percentages of eyes within ±0.25 diopters (D) and ±0.50 D of predicted refractions.

A total of 169 eyes from 167 patients were included. The RMSAEs were significantly lower with the MR biometry formula compared with the Barrett Rx formula in all 3 subgroups. In eyes with IOLs fully in the capsular bag, haptics in the bag with anterior optic capture, or haptics in the ciliary sulcus with posterior optic capture, using MR biometry and Barrett Rx formulas, respectively, 46.5% and 34.2% (P = 0.018), 47.4% and 15.8% (P = 0.041), and 41.7% and 13.8% (P = 0.016) of eyes were within ±0.25 D of predicted refractions; 69.3% and 63.2% (P = 0.296), 68.4% and 21.1% (P = 0.008), and 55.5% and 25.0% (P = 0.010) of eyes were within ±0.50 D of predicted refractions. In all 3 subgroups, both the mean and median absolute errors were lower with the MR Biometry formula than with the Barrett Rx formula.

The MR biometry formula demonstrated superior refractive accuracy compared with the Barrett Rx formula for eyes undergoing IOL exchange. These findings support its potential as a valuable tool for improving the refractive accuracy of IOL exchanges.

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