Association Between Zone-Based Scheimpflug-Placido Keratometry And Refractive Accuracy Using The Escrs Iol Calculator

To evaluate the refractive performance of the ESCRS online IOL calculator using optical biometry and Scheimpflug-derived keratometric measurements, and to investigate the impact of keratometric measurement zone on prediction accuracy compared with the conventional SRK/T formula

Department of ophthalmology, Zonguldak Bülent Ecevit University Faculty of Medicine, Zonguldak, Türkiye.

A total of 147 eyes undergoing uncomplicated cataract surgery with monofocal IOL implantation were included. IOL power was calculated using optical biometry and SRK/T based on standard keratometry. Scheimpflug-Placido imaging provided SimK and zone-averaged K values within 3, 5, and 7 mm. One-month refraction was analyzed using the ESCRS calculator (Barrett UII, EVO 2.0, Kane, Pearl-DGS, Hill-RBF, Hoffer QST, Cooke K6). MPE, MAE, MedAE, and proportions within ±0.5, ±1, and ±2 D were assessed. Statistical analyses included RM-ANOVA, Friedman, Cochran Q, McNemar, and linear mixed modeling.

Significant differences were observed among keratometric values across zones (p<0.001). Mean values were 43.3D (3mm), 43.2D (5mm), 42.9D (7mm), and 41.5D (SimK).A mixed-effects model showed a +0.039D/mm hyperopic shift (p<0.001), corresponding to +0.12D between SimK and 3mm zone. Within ±0.5D, Hill-RBF showed the highest accuracy with SimK (71.9%,p=0.012), Hoffer QST at 3mm (67.1%, p=0.053), Hill-RBF at 5mm(69.2%,p=0.038), and Hoffer QST at 7mm (65.8%, p=0.69;NS). SRK/T achieved 63.1%. No differences were found within ±1 or ±2D.

Compared with SRK/T, certain modern formulas demonstrated improved accuracy within ±0.5D in specific keratometric zones. A significant hyperopic shift was observed with increasing measurement diameter, indicating systematic zone-dependent variation in refractive prediction. Although overall accuracy within broader error ranges was comparable among formulas, performance varied according to the selected keratometric zone. These findings suggest that keratometric measurement diameter influences refractive prediction and should be considered in IOL power calculation.