Intraocular Lens Power Calculations in Long Eyes

Abstract

In eyes with axial lengths greater than 25.0 mm, intraocular lens (IOL) power calculation formulas tend to suggest IOLs of insufficient power, leaving patients with postoperative hyperopia. This chapter describes the development and validation of a method for optimizing axial length to improve the accuracy of these formulas. In consecutive cases, refractive prediction errors with the Holladay 1, Haigis, SRK/T, and Hoffer Q formulas were evaluated. Eyes were then randomized into two groups, one to develop regression formulas to optimize axial length and one to validate the method. Two additional data sets were used for validation in this original study, as well as another data set that is yet unpublished. The method of optimizing axial length significantly reduced the mean numerical refractive prediction errors: (1) for IOLs > 5.00 diopters (D), from a range of +0.27 to +0.68 D to a range of −0.10 to −0.02 D, and (2) for IOLs ≤5.00 D, from a range of +1.13 to +1.87 D to a range of −0.21 to +0.01 D (all P < 0.05). Optimizing axial length also significantly reduced the percentage of eyes that would be left hyperopic in the two additional published data sets and in a more recent set of unpublished data. The unpublished data set also demonstrated better accuracy with optimized axial lengths in comparison to the Barrett Universal Formula. In conclusion, optimizing axial length with the proposed formulas in this chapter reduced the percentage of long eyes that would end up with an undesired hyperopic outcome.