Ultrasound of the horizontal rectus muscle insertion sites: Implications in preoperative assessment of strabismus

PURPOSE. To determine the reproducibility and accuracy of ultrasonographic (LIS) measurements of distances between the corneoscleral limbus and the insertion bite of the medial (MR) or lateral rectus (LR) muscle compared with intraoperative measurements in patients with strabismus. METHODS. One eye in each of 17 patients with postoperative secondary strabismus caused by over- or undercorrected eso-and exotropia and one eye of each of 19 patients with previously untreated strabismus underwent five repeated measurements by high-resolution ultrasonography of the distance from the corneoscleral limbus to the muscle insertion and three actual intraoperative measurements. Reproducibility, expressed as the coefficient of variation, accuracy (relative error) of US measurements, and the agreement with intraoperative measurements were assessed. RESULTS. The coefficients of variation for US data were 2.02% and 18% for the MR and 7.33% and 11.77% for the LR, in the surgical and untreated groups, respectively. The relative error was 6.15% +/- 8.14% (mean +/- SD) and 3.66% +/- 12.83% for the MR muscle, and 12.21% +/- 10.66% and -7.69% +/- 7.83% for the LR muscle, in the surgical and untreated groups, respectively. The 95% limits of agreement (mean 2 SD) between the US and intraoperative measurements were 0.65 +/- 1.82 and 0.15 +/- 1.42 ram for the MR muscle, and 1.12 +/- 2.01 and -0.49 +/- 0.98 mm for the LR muscle, in the surgical and untreated groups, respectively. CONCLUSIONS. The results indicate good reliability and accuracy of US readings and suggest a potential usefulness in preoperative assessment of patients with strabismus with surgical failure and missing preoperative clinical data.