Which IOL calculation formula should you use for different scenarios?

For many years we have been instructed to use theoretical formulae to do our IOL calculations. These formulae include the third-generation Holladay 1, SRK/T and Hoffer Q, as well as the fourth-generation Holladay 2, Haigis, Olsen and Barrett methods. All of these formulae have similarities, but they also have differences and eyes in which they are particularly well suited and eyes in which they are less accurate. There are additional modifications to these formulae, such as the Wang-Koch axial length adjustment for highly myopic eyes, in an effort to improve accuracy. So it begs the question, “When do we use which formula in order to achieve the most accurate results?”I think that we may have entered a new era of IOL calculations. In my previous column, I wrote about the concept of a “Super Surface” and a “Super Formula” as published by John Ladas, MD, PhD, and his co-authors. It is an important concept that may change the way that we approach IOL calculations for our cataract surgery patients.