To determine the accuracy of wide-field ultrasound biomicroscopy (UBM) in measuring the distance between rectus muscle insertions and the corneal limbus in strabismus reoperations.

In a prospective, masked, observational study, 28 subjects with a history of horizontal rectus muscle surgery who required further surgery on horizontal rectus muscle(s) were recruited. All wide-field UBM measurements were carried out under topical anesthesia using a 50 MHz linear probe without immersion cup and external caliper. Using the caliper tool of the UBM device, the insertion-angle distance was measured. The actual muscle insertion distance from limbus was considered as measured distance plus 1 mm. The distance from muscle insertion to the limbus was also measured intraoperatively. The results of UBM and surgical measurements were compared with each other.

53 horizontal muscles [30 medial rectus (MR) and 23 lateral rectus (LR)] were included. The longest distance of the muscle insertion from limbus detectable by UBM was 13mm for MR and 15mm for LR muscle. In 38 muscles (71.7%), UBM and surgical measurements were within 1mm of each other. Only in one muscle (1.9%), the difference between measurements was more than 2mm (2.3mm). Intraclass correlation coefficient was 0.87, demonstrating excellent agreement between the two measurements. In the 95% limit of agreement analysis, MR muscle and consecutive XT cases had better agreement between two measurements.

Wide-field UBM was helpful in the preoperative assessments of patients with previous strabismus surgery. The results were more accurate for the MR and for cases of consecutive XT.