Ultrasound Biomicroscopy in Strabismus Surgery: Efficacy in Postoperative Assessment of Horizontal Muscle Insertions

Abstract

ABSTRACTPurpose: To study the efficacy of ultrasound biomicroscopy (UBM) in assessment of extraocular muscle insertion sites after strabismus surgery.Methods: This double masked prospective interventional study included 16 eyes of 15 patients with deviation <60 prism diopters (PD) who underwent primary horizontal strabismus surgery. Preoperative muscle insertion was measured by UBM and compared with measurements done intraoperatively by surgical caliper. Both measurements by surgical caliper were taken intraoperatively before and after performing the planned repositioning of the muscle insertion. Postoperatively muscle insertion was remeasured by UBM and compared with the presumed muscle insertion after surgery. Clinically limits of agreement of ± 1 mm were taken as acceptable.Results: Mean age of patients was 21 ± 3 years (range 16–28 years). Preoperative average distance of the medial rectus (MR) from limbus was 5.3 ± 0.3 mm (4.9–5.9 mm) by the UBM and 5.6 ± 0.3 (5–6 mm) by surgical caliper (p = 0.05). For lateral rectus (LR), UBM measurements from the limbus were 6.8 ± 0.7 mm (5.9–8.3 mm) and 7.1 ± 0.4 mm (6.5–8 mm) by calipers (p = 0.067). Post–op UBM at 3 months could visualize new muscle insertion for all operated MR muscles (i.e., 100% of cases) and for LR muscles in only 50% of cases. However, accuracy could be achieved only in 78.6% of cases for MR muscle and for LR in 62.5% of cases (among LR muscles that were visible post-op). Maximum distance posterior to the limbus that the UBM was able to detect MR was 11.2 mm and for LR was 13.5 mm.Conclusion: UBM does not detect the new position of LR with any consistency postoperatively. Even after detection of muscle, the new insertion is only within ±1 mm of the actual muscle insertion in 62.5% of the cases. Hence it is not a reliable tool for planning resurgery.