Even with advances in biometry and formulas, certain outlier eyes undergoing cataract surgery have higher rates of "missing the mark" than others. In general, I have found that shorter axial–length eyes requiring higher-powered intraocular lenses (IOLs) tend to have larger residual refractive errors than longer eyes requiring lower-powered IOLs.
Experts have attributed causes to this effect, including issues with effective lens position, anatomic variability in short eyes, and high IOL powers having a wider range of tolerances. It was traditionally taught that outcomes in shorter eyes are more predictable with the Hoffer Q formula, although in recent years many clinicians have come to rely on newer formulas for short, long, and normal eyes, such as the Barrett Universal II.
In a recently published multicenter retrospective case series, Kane and Melles compared the accuracy of IOL formula predictions in 182 patients with extreme axial hyperopia implanted with the Alcon SA60AT IOL of ≥ 30 diopters. Optimized IOL constants were used for all of the formulas in order to give them the best chance of predicting the resultant refractive outcome.
The authors found that the Kane formulahad the lowest mean absolute prediction error when compared with the Barrett Universal II, Emmetropia Verifying Optical (EVO) 2.0, Haigis, Hill-RBF 2.0, Hoffer Q, Holladay 1, Holladay 2, Olsen 4-factor, and SRK/T formulas. This was statistically significant for all formulas except the EVO 2.0. They concluded that using the Kane or EVO 2.0 formula will increase predictability by about 20% in this group of patients when compared with the Barrett or Hoffer Q formula.
