Intraoperative Biometry as Alternative to Conventional Methods for Predicting IOL Power
Purpose
To compare intraoperative biometry (IRB) for intraocular lens (IOL) power calculation to conventional methods.
Methods
This series included 529 patients undergoing primary cataract surgery and IOL implantation. Subgroups included axial lengths <22mm or >25mm (n=216,) post-refractive surgery (n= 35), and eyes with toric lenses (n=52). Preoperatively, all patients underwent biometric measurements to guide IOL choice. IRB (ORA; WaveTec Vision, Inc.) was done to determine the aphakic refraction which was plugged into a modified vergence formula for IOL power. The predictive accuracy of conventional methods (i.e. Holladay 1/2, Haigis, and SRK-T) was compared to ORA (mean absolute error = actual spherical equivalent (SE) – predicted SE). The percentage of eyes within ± 0.50 diopters (D) and ± 1.00 D of the refractive target was calculated.
Results
There was no statistical difference between conventional methods and ORA in any of the subgroups aside from the toric subgroup (MAE 0.39±0.30 (conventional) vs 0.25±0.22 (ORA), p=0.005). The ORA resulted in more patients achieving a spherical equivalent within 0.50 D of the target, particularly in the short eyes and post-myopic laser vision correction subgroups, but this did not achieve statistical significance.
Conclusion
In our study, the power estimation in eyes undergoing toric IOLs was more accurately predicted by ORA than conventional methods. In all other categories there were no statistical differences between the groups. We suspect that a larger, multicenter study needs to be done in order to determine if there is a significant different in the remainder of the subgroups.