Improving accuracy of phakic intraocular lens sizing using high-frequency ultrasound biomicroscopy

PURPOSE: To assess the efficacy of high-frequency ultrasound biomicroscopy (UBM) in improving the accuracy of phakic intraocular lens (pIOL) sizing by increasing the incidence of acceptable postoperative vault. SETTING: Multiple private practices, United States. DESIGN: Evaluation of diagnostic test or technology. METHODS: This prospective multicenter clinical study evaluated eyes having pIOL (Visian Implantable Col lamer Lens) implantation. A retrospective data analysis was performed using UBM measurements (VuMax-II) of preoperative sulcus-to-sulcus (STS) distance and postoperative vault. The regression data and clinical input from investigators were then used to develop a pIOL sizing nomogram. The nomogram used only STS and pIOL power as variables to determine length. Inadequate vault (<90 mu m) and excessive vault (>1000 mu m) were defined based on peer-reviewed literature. Sizing recommendations using the nomogram were studied prospectively and compared with 2 sizing methods used in the United States that are based on white-to-white (WTW) measurements. RESULTS: One eye was excluded from the analysis because the wrong length pIOL was placed (12.6 mm instead of nomogram-recommended 13.2 mm), resulting in 51 mu m of vault. The mean postoperative vault in the remaining 72 cases was 340 mu m +/- 174 (SD) (range 90 to 952 pm); there were no cases of inadequate or excessive vault with the newly developed UBM nomogram. Sizing methods using WTW measurements would have resulted in different-sized pIOLs in 36% to 69% of cases compared with the STS method. CONCLUSION: There were no cases of inadequate or excessive vault when the UBM nomogram for pIOL sizing was used.