Formula Discordance and Refractive Target Error: Temporal Validation of Legacy–Modern Intraocular Lens Formula Disagreement as a Quality-Control Marker
Ali Altan Ertan Boz, Bülent ÇüçenPurpose:
To determine whether disagreement between third-generation and modern intraocular lens (IOL) formulas identifies eyes at increased risk of refractive target error.
Setting:
Yenikent State Hospital, Sakarya, Türkiye.
Design:
Retrospective cohort with chronological derivation and temporal validation.
Methods:
Six hundred eyes with foldable one-piece IOL implantation were analyzed. Third-generation formulas were SRK/T, Hoffer Q, and Holladay 1; modern formulas were Barrett Universal II, Kane, EVO 2.0, PEARL-DGS, and Cooke K6. Formula-specific offsets were estimated in 400 earlier eyes and frozen for 200 later validation eyes. The Legacy–Modern Gap (LMG) was the absolute difference between mean predicted postoperative spherical equivalent of the 2 formula groups. The primary endpoint was an absolute target miss of at least 0.50 D.
Results:
Target miss occurred in 29.0% of derivation eyes and 26.0% of validation eyes. Validation mean absolute error was 0.284-0.317 D for modern formulas and 0.358-0.424 D for third-generation formulas (P<0.001). Each 0.10 D increase in LMG was associated with target error (adjusted odds ratio, 1.21; 95% CI, 1.05-1.38; P=0.007). Validation AUC was 0.650 versus 0.603 for biometrics alone (ΔAUC, 0.047; 95% CI, -0.015 to 0.111). Brier score improved by 0.0116 (95% CI, 0.0034-0.0200); calibration intercept was 0.01 and slope 1.25.
Conclusions:
Formula disagreement added information beyond biometrics but had modest discrimination. LMG is a supplementary quality-control signal rather than an independent rule for IOL selection.