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

Abstract

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

Methods: 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.

Results: 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.

Conclusion: 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.