Accuracy of the Ultrasound Biomicroscopy Bag/Balloon Technique in Locating Horizontal Extraocular Muscle Insertions Before and After Strabismus Surgery

Comparison of anterior segment optical coherence tomography and ultrasound biomicroscopy in localizing horizontal rectus muscle insertions

PURPOSE

To evaluate the viability and precision of measuring the distance from the limbus to extraocular muscle insertion using anterior segment optical coherence tomography (AS-OCT) and panoramic ultrasound biomicroscopy (UBM) before and after strabismus surgery.

METHODS

We recruited primary strabismus patients and measured the limbus-insertion distance by AS-OCT and UBM preoperatively, 2 weeks, and 1, 3, and 6 months postoperatively. Values were also measured using callipers intraoperatively before and after the planned procedures. Preoperative AS-OCT and UBM values were compared to intraoperative calliper measurements as the gold standard. Postoperative AS-OCT and UBM values were compared to the new postoperative limbus-insertion distance. The limit of agreement deemed clinically acceptable was defined as 1 mm.

RESULTS

A total of 85 horizontal muscles of 40 patients, including 48 lateral rectus muscles and 37 medial rectus muscles, were analysed. Primary muscles could be successfully detected by AS-OCT (95%) and UBM (100%). At 2 weeks and 1, 3, and 6 months postoperatively, the new rectus muscle attachment site detection rate by AS-OCT was 6%, 32%, 80%, and 89%, respectively, and that by UBM was 24%, 60%, 85%, and 93%, respectively. The Bland-Altman plots revealed better consistency in pairs of AS-OCT, UBM, and calliper measurements of primary muscles than postoperative muscles. For primary muscles, 89% of AS-OCT measurements fell within the permissible range of surgical measurements (1 mm), but this dropped to 67% at 6 months postoperatively (P < 0.001). The accuracy of UBM measurements of primary muscles was 81%, and this decreased to 59% at 6 months postoperatively (P = 0.001).

CONCLUSIONS

AS-OCT and UBM performed well in terms of imaging primary horizontal rectus muscles, but showed decreased accuracy and reproducibility in postoperative muscle measures.

Comparison of the swept-source anterior segment optical coherence tomography and wide-field ultrasound biomicroscopy for imaging previously operated horizontal extraocular muscles

PURPOSE

To assess the feasibility and accuracy of determining extraocular muscle insertion distance from the limbus of previously operated extraocular muscles with the swept-source anterior segment optical coherence tomography (AS-OCT) compared with wide-field ultrasound biomicroscope (UBM).

METHODS

Patients with a history of previous strabismus surgery for whom additional strabismus surgery was planned were enrolled. The insertion distance was measured by AS-OCT and UBM before reoperation and compared to the caliper measurement at the time of surgery. Observers taking measurements were masked to patient data. Patient comfort for both machines was graded on a scale of 1-10 and timing of both imaging procedures was recorded.

RESULTS

Thirteen previously operated muscles of 6 subjects (age 20.3 ± 4.4 years; range, 11-25) were imaged. The muscle insertion could be identified in 12 cases on AS-OCT and 10 cases on UBM. The difference between the imaging result and the caliper reading was ≤1 mm in 9 cases on AS-OCT and 5 cases on the UBM (69% vs 38%; P = 0.03). The maximum insertion distance on AS-OCT was 13.8 mm; on UBM, 10.4 mm. AS-OCT had a higher grade than UBM for patient comfort (P = 0.0005) and speed (P = 0.001).

CONCLUSIONS

In our cohort, AS-OCT identified the muscle insertion distance more accurately than UBM. AS-OCT measurements were judged more comfortable to the patient, and images were acquired faster. In large recessions, wide-field UBM yields suboptimal results compared with AS-OCT.