Relative Behavior of Modern Intraocular Lens Power Calculation Formulas Across a Realistic Range of Biometry Values

To investigate the relative performance of modern intraocular lens (IOL) power calculation formulas over a wide range of biometric parameters.

Through the concept of emmetropization there exists a mean keratometry, anterior chamber depth, lens thickness, and white-to-white for a given axial length (AL). Using a database of biometric values from 2721 surgery naïve eyes, these relationships were modeled and used to create an artificial dataset of 170 eyes with an anatomically realistic distribution of biometric parameters. Biometric values for each artificial eye were entered into the ESCRS IOL power calculation website. The emmetropic IOL power was calculated for Barrett Universal II, Cooke K6, Kane, PEARL-DGS, HofferQST, EVO v2.0, and Hill-RBF v3.0. Separately, emmetropic IOL powers were calculated for the Zeiss AI formula. The disparity between the formulas was evaluated to determine the ALs at which they diverged.

For eyes with ALs between 22.5 and 28.1 mm, emmetropic IOL powers and spherical equivalent predictions differed by less than 0.25 D. Outside this range, spherical equivalent predictions differed by 0.25 D or more. At ALs < 19.5 mm the difference in emmetropic IOL power across the formulas exceeded 1.0 D.

This work helped to identify an implementation error in Pearl-DGS, which was corrected in collaboration with the formula's author. Cataract surgeons should consider that formula choice still has a clinically meaningful impact on refractive outcomes in eyes with axial lengths of <22.5 mm and >28.1 mm. We estimate that this may represent more than 10% of the population.