The accuracy of wide-field ultrasound biomicroscopy in localizing extraocular rectus muscle insertions in strabismus reoperations

Abstract

To compare the accuracy of widefield ultrasound biomicroscopy (UBM) with mechanical intraoperative measurements of the distance between rectus muscle insertions and the corneal limbus in strabismus reoperations. Subjects with a history of horizontal rectus muscle surgery who required further surgery on horizontal rectus muscle(s) were recruited prospectively. All widefield UBM measurements were carried out under topical anesthesia using a 50 MHz linear probe without immersion cup and external caliper. The insertion angle distance was measured using the caliper tool of the UBM device; the actual muscle insertion distance from the limbus was considered to be the 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. A total of 28 subjects were recruited, and 53 horizontal muscles (30 medial rectus, and 23lateral rectus muscles) were included. The longest distance of the muscle insertion from limbus detectable on UBM was 13 mm for the medial rectus muscle and 15 mm for the lateral rectus muscle. In 38 muscles (71.7%) UBM and surgical measurements were within 1 mm of each other. Only in 1 muscle (1.9%) was the difference between measurements >2 mm (2.3mm). The intraclass correlation coefficient was 0.87, demonstrating excellent agreement between measurements. Limit of agreement analysis demonstrated better agreement between measurements of medial rectus muscles and in consecutive exotropia cases. This study demonstrated good agreement between intraoperative and widefield UBM measurements of the muscle insertion-limbus distance in our patient cohort.