Viewpoint

Deleting fudge from the IOL recipe

FROM THE CHIEF MEDICAL EDITOR

Larry E. Patterson, MD

Ophthalmologists just love fudge factors to make an IOL calculation. Long ago, even before my time, surgeons used a table to try to convert preoperative refraction to the best power IOL to implant during cataract surgery. But, in 1981 came the SRK formula. That worked reasonably well for average eyes, but so-so with most others. In 1988, the SRK II added a fudge factor to account for both smaller and larger eyes, and it helped some more.

EVEN MORE ACCURACY

Theoretical formulae like the SRK/T, Holladay 1 and Hoffer Q increased accuracy even more. But there were guidelines, such as using Hoffer Q for shorter eyes, Holladay 1 for average eyes and SRK/T for longer eyes. Unless, of course, the eye had funny Ks, in which case the SRK/T might be more prone to issues since it relies more heavily on the K value to determine the effective lens position. Also, when dealing with a longer axial length, the Wang-Koch modification uses a different calculation for each theoretical formula to adjust the axial length. Don’t forget to add this new value to re-calculate the IOL power. And remember that with post-refractive surgery eyes, all of the above probably should be tossed, as there are another 20 or so methods to calculate the IOL. To further increase accuracy, we can include more preoperative data such as anterior chamber depth, white-to-white, and other factors into more advanced systems like Holladay 2, Haigis, Barrett and Olsen.

So if I’m concerned about the patient’s visual outcome I can calculate the IOL power myriad ways, but what happens when I get different answers? Seriously, there has to be a better way.

KNIGHTS WITH SHINING CALCULATORS

John Ladas, MD, PhD and colleagues are developing a novel method to incorporate all current and future formulae (and all fudge factors) into one cohesive “Super Formula”. These formulae will be plotted in 3-D onto a Super Surface. The Super Formula is dynamic so that data from prior calculations and surgeries can be used to further refine the results both for the individual and a large cohort of surgeons. In the initial trial of 100 varied eyes, the Super Formula chose the best IOL power each time. Other formulae didn’t fare as well, with scores between 52% and 84% correct.

This is all new to me, and I have no idea how it will all work, but these new applications may revolutionize IOL power calculations and put an end to ophthalmic fudge factors. OM