Evaluation of Sum of Segments Biometry in Modern Intraocular Lens Power Calculation Formulas for Long Eyes

To evaluate the sum of segments (SOS) biometry in modern intraocular lens power (IOL) calculation formulas for long eyes.

This was a retrospective case series that included 177 eyes from 177 patients with axial length (AL) ≥ 24.5 mm. Preoperative AL measurements were performed using the ARGOS (Alcon, Inc). This study used 2 formulas: the Barrett Universal II (BUII) and the Barrett true axial length (BTAL). Other formulas were included: Cooke K6, EVO 2.0, and PEARL DGS.

The Barrett Universal II formula exhibited the most significant myopic mean prediction error at -0.15 ± 0.27 D, with the Cooke K6, PEARL-DGS, and EVO 2.0 formulas following. In terms of hyperopic mean prediction error, the PEARL-DGSsos formula recorded the highest value at 0.19 ± 0.32 D, succeeded by the EVO 2.0sos, Cooke K6sos, and BTAL formulas. The EVO 2.0, PEARL-DGS, Barrett Universal II, and Cooke K6 formulas demonstrated the lowest mean and median absolute errors, with BTAL, EVO 2.0sos, Cooke K6sos, and PEARL-DGSsos formulas trailing behind. The median absolute errors (MedAE) for EVO 2.0, PEARL-DGS, and Barrett Universal II were recorded at 0.13, 0.15, and 0.16 D, respectively.

BUII formula showed myopic shift with SOS biometry which increases with longer eyes. Using SOS option in Cooke K6, EVO 2.0, and PEARL-DGS formulas leads to a hyperopic shift in the mean prediction error which is undesirable. Using ALsos in those formulas without choosing the option of SOS yields a mean prediction error towards the myopic side which might be more desirable. All included formulas performed well with ALsos with most of the cases within + 1 D of intended refraction.