Anterior Segment Optical Coherence Tomography in Locating the Insertion of Horizontal Extraocular Muscles After Strabismus Surgery

Agreement between intraoperative and anterior segment optical coherence tomography measurements of the extraocular muscle insertion distance in patients with previous strabismus surgery

PURPOSE

To evaluate the agreement between anterior segment optical coherence tomography (AS-OCT) measurement of preoperative distance from the limbus to the horizontal rectus muscle insertion and intraoperative measurement in patients who have previously undergone strabismus surgery and required reoperation.

METHODS

Subjects from two ophthalmological centers were included. Preoperative AS-OCT was used to measure the muscle insertion from the limbus, and intraoperative measurements were obtained using calipers. Interclass correlation coefficient and Bland-Altman agreement analysis were used.

RESULTS

A total of 53 horizontal rectus muscles from 24 patients with previous strabismus surgery were analyzed: 27 medial rectus (MR) and 26 lateral rectus (LR) muscles, including both previously operated and previously unoperated muscles. Average of AS-OCT measurements of MR was 8.54 ± 2.42 mm and intraoperatively was 9.4 ± 3.09 mm. Average AS-OCT for LR was 8.32 ± 2.25 mm and intraoperatively was 9.34 ± 3.73 mm. 63% of MR muscles and 77% of LR muscles were within 1 mm between AS-OCT and intraoperative measurement. Spearman's correlation coefficient showed positive correlation between measures for both MR and LR muscles. The interclass correlation coefficient was 0.79 (95% CI, 0.56-0.90) for MR muscles and 0.70 (95% CI, 0.44-0.85) for LR muscles, with a good agreement. Agreement was better for muscles ≤10 mm from the limbus (which included both previously operated and unoperated muscles) than for muscles found >10 mm from the limbus.

CONCLUSIONS

Good agreement was observed between the measurement of limbus-insertion distance obtained by AS-OCT and by intraoperative measurement, especially when the muscle insertion was ≤10 mm from the limbus.

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.

Defining the Clinical Role of Swept-Source Anterior Segment Optical Coherence Tomography in Eyes Undergoing Strabismus Surgery

Purpose

To describe the clinical role of swept-source anterior segment optical coherence tomography in extraocular muscle imaging in various strabismic conditions.

Study Design

Prospective observational study.

Participants

A total of 1104 extraocular muscles of 150 subjects were imaged. Normal eyes (640 muscles), eyes undergoing re-operation (240 muscles), paralytic strabismic eyes (16 muscles), non-paralytic strabismic eyes (20 muscles), post-traumatic strabismic eyes (64 muscles), eyes with thyroid disease (64 muscles), and other atypical cases (60 muscles) were imaged. In all cases, up to four recti muscles were evaluated in a given eye depending on the need.

Results

The mean age was 38.15 ± 16.25 years. Overall, muscle insertion was identified in over 90% of the subjects. Apart from normal muscles (n = 860, 93.68%), the location was identified in previously operated eyes (n = 54, 90%), in traumatic muscle slippage (n = 2, 11.11%), in ocular coat ectasia (n = 11, 91.66%), in thyroid muscle hypertrophy, in operated scleral fixated intraocular lens with strabismus, and other challenging cases. In all circumstances, clinically useful information was obtained from the anterior 4–14 millimetres of the rectus muscle, which in turn helped in active surgical planning and overall management.

Conclusion

The SS-ASOCT with its wider and deeper scanning abilities was able to locate the extraocular muscle insertion in a variety of strabismic conditions. Therefore, this tool can be used in the preoperative periods for optimal surgical planning and management.

Correlation between Thyroid-stimulating Antibody Level Change and Extraocular Muscle Thickness Change in Thyroid Eye Disease

Purpose: To investigate the changes in extraocular muscle thicknesses by variations in the thyroid stimulating antibody (TSAb) level in patients with thyroid eye disease (TED).Methods: A total of 67 TED patients were enrolled. They were divided into two groups: an experimental group with clinically significant elevated TSAb levels (≥140 IU/L) and a control group (TSAb <140 IU/L). All of the lateral, medial, superior, and inferior rectus muscle thicknesses were measured with the aid of anterior segment optical coherence tomography (OCT). The average thicknesses for both eyes were recorded for each patient based on the values measured at the ends of the muscles (which become vertically thinner from the points of tendon attachment). We measured changes in TSAb levels and extraocular muscle thicknesses after two follow-up periods and sought correlations among these parameters.Results: At the initial visits, the inferior rectus muscle thickness was positively correlated with the TSAb level in the experimental group (p = 0.045, r = 0.478). None of the medial, superior, or lateral rectus muscle thicknesses were so correlated. On follow-up, the variation in TSAb level correlated negatively with changes in lateral rectus muscle thickness (p = 0.038, r = -0.357). The superior rectus muscle thickness tended to be negatively correlated with the TSAb level, but statistical significance was not attained (p = 0.146, r = -0.669). The thicknesses of the inferior and superior rectus muscles did not change over time.Conclusions: In TED patients, TSAb variations seem to reflect the extent of periorbital tissue edema, thus correlating negatively with especially lateral rectus muscle thickness changes.