Abstract
Purpose :
Modern IOL power calculation formulas perform similarly in eyes of nominal axial length, keratometry and anterior chamber depth. The purpose of this study was to investigate how modern IOL formulas perform relative to each other over a wide range of axial lengths.
Methods :
Through the principle of emmetropization, there exists a mean keratometry (K), anterior chamber depth (ACD), lens thickness (LT), and white-to-white (WTW) for a given axial length (AL). Using a database of ocular biometric values and linear regression, expected relationships between K, ACD, LT, WTW and AL were derived. Using these derivations, an artificial dataset of eye biometries was created that spanned a range of axial lengths from 17.0 - 35.0 mm. Biometric values for each artificial eye were entered into the ESCRS IOL power calculation website. Through extrapolation, the IOL powers corresponding to exact emmetropia (0.00 D) were calculated for the Barrett Universal II, EVO v2.0, Cooke K6, Hoffer QST, Hill RBF v3.0, Kane, and Pearl DGS formulas. The disparity between formulas was studied to determine ALs at which the formulas diverged in a clinically meaningful way.
Results :
For eyes with ALs between 22.5 and 27.1 D, emmetropic IOL powers and spherical equivalent predictions differed by less than 0.375 and 0.25 D, respectively. Outside this range, formula divergence might be considered clinically meaningful, as SE predictions differed by 0.25 D or more. At very long ALs (> 30.4 mm), the Pearl-DGS formula appeared to diverge significantly from the rest of the formulas. At ALs less than 19.6 mm and greater than 32.6 mm, the difference in emmetropic IOL power across formulas exceeded 1.0 D.
Conclusions :
Cataract surgeons should consider that, even with modern formulas, formula choice can have a clinically significant impact on the refractive outcome for eyes with ALs less than 22.5mm and greater than 27.1mm. In our database of 8,264 keratometry measurements, 13.14% of eyes fell within the range of ALs where IOL formula choice might have a clinically meaningful impact.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.