Many decades ago, ophthalmologists primarily relied on preop refraction to estimate the IOL power for cataract surgery. This evolved into using the keratometry and axial length, first with regression (SRK I and SRK II) and then with theoretical formulae (Holladay 1, SRK/T and Hoffer Q). This proved reliable for most eyes, but it soon became clear that more input variables, such as anterior chamber depth, could help predict the effective lens position (ELP) of the IOL more accurately. This factor, determining the precise ELP, is the primary challenge for truly accurate IOL calculations.
We now use the keratometry and axial length as the two primary factors for IOL calculations, with other data such as anterior chamber depth, white-to-white, refraction, lens thickness and more to help hone the ELP determination. These newer formulae such as the Holladay 2, Haigis, Olsen and Barrett Universal II tend to be more accurate than their predecessors, and many surgeons have abandoned the older methods, which were based on refraction, regression and only two-input variables.
Lens calculation methods continue to evolve, and there will be more factors that play a role in honing IOL calculations, such as the lens equatorial plane as mentioned in this study by Dr. Yoo and colleagues. Based on this study, lens equatorial plane appears to be an important factor that can be incorporated into our calculations. And there may be more important variables in the future such as posterior corneal power and angle measurement.
One thing is certain: Methods of IOL power calculation will continue to evolve, and static formulae will eventually become outdated. This is why the future of IOL calculations will be using methods such as artificial intelligence, neural networks and big data. This new technology is embraced by the Hill-RBF and the Ladas Super Formula 2.0 Artificial Intelligence. These machine learning methods will be able to incorporate new factors such as lens equatorial plane to become more accurate. Already, we can achieve more than 90% of patients within 0.5 D of target, and that is a huge improvement compared with just a decade ago.
Uday Devgan, MD
Healio.com/OSN Section Editor
Disclosures: Devgan reports he is a principal in Advanced Euclidean Solutions, which owns the Ladas Super Formula, and the www.iolcalc.com website, which is free to all users.