Evaluation of vertical rectus muscles using ultrasound biomicroscopy

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.

A systematic review of ultrasound biomicroscopy use in pediatric ophthalmology

Ultrasound biomicroscopy (UBM) is the only available option for noninvasive, high-resolution imaging of the intricate iridociliary complex, and for anterior segment imaging with corneal haze or opacity. While these unique features render UBM essential for specific types of trauma, congenital anomalies, and anterior segment tumors, UBM imaging has found clinical utility in a broad spectrum of diseases for structural assessments not limited to the anterior intraocular anatomy, but also for eyelid and orbit anatomy. This imaging tool has a very specific niche in the pediatric population where anterior segment disease can be accompanied by corneal opacity or clouding, and anomalies posterior to the iris may be present. Pediatric patients present additional diagnostic challenges. They are often unable to offer detailed histories or fully cooperate with examination, thus amplifying the need for high-resolution imaging. This purpose of this systematic review is to identify and synthesize the body of literature involving use of UBM to describe, evaluate, diagnose, or optimize treatment of pediatric ocular disease. The collated peer-reviewed research details the utility of this imaging modality, clarifies the structures and diseases most relevant for this tool, and describes quantitative and qualitative features of UBM imaging among pediatric subjects. This summary will include information about the specific applications available to enhance clinical care for pediatric eye disease.

Horizontal Extraocular Muscle Insertion Site in Relation to Axial Length Using Swept-Source Anterior Segment OCT

Purpose

The purpose of this study was to correlate between the axial length of the globe and the insertion site of horizontal extraocular muscles using swept-source anterior segment optical coherence tomography (SS-ASOCT), with posing an equation to calculate the muscle insertion site from the axial length.

Methods

The study design was observational and cross-sectional. It was performed on 157 eyes of 157 healthy subjects. The distance of the medial rectus (MR) and the lateral rectus (LR) insertion sites from the limbus were measured using SS-ASOCT. The insertion sites’ distances were correlated to the axial length (hypermetropes < 22.5 mm, myopes > 24.5). Correlation between numerical variables was done by Pearson’s correlation coefficient and confirmed by linear regression analysis and scatter diagrams.

Results

The mean MR insertion site was 5.47 ± 0.19 mm in hypermetropes versus 5.68 ± 0.23 mm in myopes, whereas the mean LR insertion site was 6.81± 0.23 mm in hyperopes versus 7.08 ± 0.16 mm in myopes. The axial length showed a moderate positive, but significant, correlation to the insertional position for the medial and lateral rectus muscles (MR: r=0.417, p<0.001; LR: r=0.410, p<0.001).

Conclusion

Comparing the horizontal extraocular muscle insertion site to axial length using SS-ASOCT showed a significant positive correlation. The model equation for MR insertion: MR (mm) = 4.522 + 0.045 (AXL in mm) with an R = 0.437, R²= 0.191, F=12.071, P<0.001. The model equation for LR insertion: LR (mm) = 5.72 + 0.048 (AXL in mm) with an R = 0.438, R²= 0.192, F=12.116, P<0.001.

Accuracy of anterior segment optical coherence tomography for pre-operative localization of insertions of extraocular recti muscles

Introduction:

To study the accuracy of anterior segment optical coherence tomography (AS-OCT) function of Cirrus HD-OCT 500 (Carl Zeiss Meditec, Dublin, CA) in calculating the insertion of rectus muscles from the limbus in patients undergoing primary squint surgery.

Methodology:

A prospective, double-masked, observational study was conducted on 128 muscles of 46 patients with strabismus who were planned for strabismus surgery between January 2019 and December 2019. Insertion distance from limbus was measured using AS-OCT function of Cirrus HD-OCT 500 preoperatively. Intraoperative measurements were taken using Castroviejo caliper. A Bland-Altman analysis was performed to determine the agreement between the readings.

Results:

A total of 128 muscles were successfully imaged and evaluated, including 13 superior recti (10.15%), 23 inferior recti (17.96%), 35 medial recti (27.34%) and 57 lateral recti (44.53%). 124 muscles (96.9%) were within 1mm difference, which was considered clinically acceptable. Bland-Altman plots showed the level of agreement between the two methods was good.

Conclusion:

Anterior segment scan function of Cirrus HD-OCT 500 is an accurate method to detect the insertion of extraocular recti muscles in patients of primary strabismus surgery.

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

PURPOSE

To investigate the accuracy of high frequency ultrasound biomicroscopy using the bag/balloon technique to locate recti muscle insertions before and after strabismus surgery.

METHODS

This was a prospective masked study. The distance from the limbus to horizontal recti muscle insertions was measured by caliper intraoperatively and ultrasound biomicroscopy preoperatively and during follow-up. Accuracy was defined as the difference between ultrasound biomicroscopy and caliper measurements.

RESULTS

Thirty-nine muscles (19 medial rectus and 20 lateral rectus) of 22 patients were included. The mean age of the patients was 34.7 ± 15.5 years (range: 18 to 78 years). Follow-up measurements were available for 25 muscles: 12 muscles were recessed and 13 were resected/advanced. Twelve of the included muscles underwent prior surgery. There was a strong correlation between preoperative mean ultrasound biomicroscopy and caliper measurements (P < .001, r_p = 0.872) without significant difference between the accuracy of identification of medial rectus and lateral rectus muscles (P = .116 and .377, respectively). On average, postoperative ultrasound biomicroscopy measurements of recessed muscles were 1.15 mm greater than caliper measurements at the end of surgery (P = .003), whereas the mean difference in the resected muscles was not statistically significant (-0.07 mm, P > .999). Overall, in 16 of 25 muscles (64%), the differences between the postoperative measurements and the end of surgery measurements were less than 1 mm. There was no correlation between the accuracy and the time of ultrasound biomicroscopy after surgery (P = .516).

CONCLUSIONS

The ultrasound biomicroscopy bag/balloon technique is an accurate and reliable method of locating recti muscle insertions before and after strabismus surgery. Ultrasound biomicroscopy may assist strabismologists in planning repeated operations. [J Pediatr Ophthalmol Strabismus. 2020;57(1):12-20.].

Pre-, Intra-, and Post-Operative Evaluation of Extraocular Muscle Insertions Using Optical Coherence Tomography: A Comparison of Four Devices

OCT (optical coherence tomography) is widely used in ophthalmology and pediatric ophthalmology, but limited research has been done on the use of OCT in strabismus. This study investigates the use of different OCT machines to image rectus muscle insertions pre-, intra-, and post-operatively in pediatric strabismus patients. The OCT machines used in the study were a Bioptigen (Leica Microsystems Inc., Buffalo Grove, IL, USA), Spectralis HRA+OCT with Anterior Segment Module (Heidelberg Engineering, Heidelberg, Germany), Visante (Carl Zeiss, Oberkochen, Germany), and Zeiss Rescan 700 (Carl Zeiss, Oberkochen, Germany). Measurements from the machines were compared with the caliper distance measured during the strabismus surgery before disinsertion or after reattachment. The OCT machines had moderate (Bioptigen: 0.62) to good intraclass correlation coefficients (Rescan: 0.83, Spectralis: 0.85, Visante: 0.88) with intra-operative measurements. To our knowledge, this is the first study to use an operating microscope with integrated intra-operative OCT to image rectus muscle insertions. OCT is a useful tool in strabismus surgical patients in the pre-, intra-, and post-operative settings, particularly in patients who have had previous surgery, when the muscle insertion is unknown. The ability to accurately image rectus muscle insertions has significant implications for the management of strabismus patients.

Magnetic Resonance Imaging of the Globe-Tendon Interface for Extraocular Muscles: Is There an "Arc of Contact"?

PURPOSE

To determine if the "arc of contact" is an accurate approximation of the globe-tendon interface for the biomechanical modeling of extraocular muscle (EOM) force transfer onto the globe.

METHODS

At a single academic institution, 18 normal and 14 strabismic subjects were prospectively recruited for surface-coil enhanced magnetic resonance imaging at 312- or 390-μm resolution in axial planes for horizontal EOMs (23 subjects, 26 orbits) and sagittal planes for vertical EOMs (13 subjects, 22 orbits) during large ipsiversive ductions. The measured angle at insertion and the predicted angle assuming an "arc of contact" were compared using paired t tests.

RESULTS

For normal EOMs, the measured angle at insertion was significantly greater than predicted assuming an "arc of contact" for the medial rectus (MR) (5.0 ± 4.8 degrees vs 0.0 ± 0.0 degrees, P = .03), lateral rectus (LR) (4.9 ± 3.0 degrees vs 0.0 ± 0.0 degrees, P = .02), inferior rectus (7.4 ± 4.8 degrees vs 1.2 ± 2.6 degrees, P = .00003), and superior rectus (0.6 ± 1.1 degrees vs 0.0 ± 0.0 degrees, P = .04). In strabismic subjects, the measured angle was significantly greater for the MR in abducens palsy (9.9 ± 4.3 degrees vs 0.5 ± 0.7 degrees, P = .0007) and after MR resection (9.0 ± 6.9 degrees vs 1.2 ± 2.4 degrees, P = .02), but not after LR recession (2.9 vs 0.0 degrees). Single subjects had comparable angles after MR recession, but markedly different angles after MR and LR posterior fixation.

CONCLUSIONS

Contrary to the "arc of contact" biomechanical model, normal and postsurgical EOMs are significantly non-tangent to the globe at their scleral insertions. The "arc of contact" should be replaced in biomechanical modeling by the experimentally measured angles at tendon insertions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

The role of imaging in strabismus

PURPOSE OF REVIEW

To review the most recent literature regarding the clinical experience of imaging modalities in strabismus.

RECENT FINDINGS

MRI of extraocular muscles (EOMs) has elucidated the roles of variation in compartmental contraction of EOMs and further evidence of EOM pulley heterotopy in various strabismus patterns, which may contribute to the clinical and surgical management of patients as this mode of imaging becomes more readily available. Ultrasound biomicroscopy (UBM) and anterior-segment optical coherence tomography (AS-OCT) may play a role in determining the location of EOMs which could also aid in devising a preoperative surgical plan, especially in those who have had prior strabismus surgery.

SUMMARY

Although MRI, UBM, and AS-OCT show promise in the formulation of a treatment plan in complex strabismus, more research regarding the role and limitations of these imaging modalities is required before they become the mainstay of strabismus evaluation.

Accuracy of Optical Coherence Tomography Measurements of Rectus Muscle Insertions in Adult Patients Undergoing Strabismus Surgery

PURPOSE

To assess the accuracy of anterior segment optical coherence tomography (AS-OCT) in measuring the distance of extraocular muscle (EOM) insertion to the limbus to improve preoperative assessment of adult patients undergoing strabismus surgery.

DESIGN

Reliability analysis.

METHODS

setting: An institutional practice.

PATIENT POPULATION

Seventy-four adult patients scheduled for strabismus surgery on rectus muscles.

OBSERVATION PROCEDURE

The distance between the EOM insertion and the limbus was measured preoperatively with AS-OCT. The value was compared with the intraoperative measurement obtained with calipers. Additional measurements included the limbus-anterior chamber angle distance with AS-OCT and the axial length with IOLMaster.

MAIN OUTCOME MEASURE

Agreement between preoperative AS-OCT and intraoperative measurements. A difference of ≤1 mm was "clinically acceptable."

RESULTS

A total of 144 muscles were analyzed. Thirty-one of 33 reoperated muscles were successfully imaged. AS-OCT measurements were within 1 mm of intraoperative measurements in 77% of all muscles. The accuracy was higher for muscles with no prior surgery (83%), as compared with reoperated muscles (58%). Although the accuracy decreased when comparing reoperations to primary surgeries for the medial (79% to 63%; P = .09; 95% confidence interval [CI], -1.38 to 0.11) and the lateral rectus (81% to 49%; P = .11; 95% CI, -2.06 to 0.22), the difference was not significant. No correlation between limbus-anterior chamber angle distance and axial length was established.

CONCLUSIONS

AS-OCT is valuable in identifying EOM insertions in primary strabismus surgeries, but the accuracy decreases in reoperations.

Limbus-insertion distance of superior rectus in primary angle closure glaucoma: an anterior segment OCT study

OBJECTIVE

To compare the distance from the corneoscleral limbus to the insertion site of the superior rectus of primary angle-closure glaucoma (PACG) patients with normal controls and to identify potential characteristics associated with limbus-insertion distance.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 92 subjects (eyes) were enrolled in the study: 35 were nonglaucoma controls and 57 were PACG patients.

METHODS

The limbus-insertion distance of the superior rectus was measured by anterior segment optical coherence tomography (AS-OCT) and intraoperative surgical caliper. The anterior chamber parameters were also measured using AS-OCT to identify potential characteristics associated with limbus-insertion distance.

RESULTS

The limbus-insertion distance of the superior rectus was 0.40 ± 0.08 mm shorter in the PACG group than in the normal control group (p < 0.001). Anterior segment parameter values, including anterior chamber depth (ACD), anterior chamber width (ACW), anterior chamber area (ACA), and anterior chamber volume (ACV), were smaller in the PACG group than in the normal control group, but the lens vault was larger (all p < 0.001). A shorter limbus-insertion distance of the superior rectus was significantly associated with shorter axial length and "crowded" angle (smaller ACD, ACW, ACA, and ACV) (all p < 0.05).

CONCLUSIONS

This is the first study to demonstrate that the limbus-insertion distance of the superior rectus was shorter in PACG eyes than in normal eyes. The shorter limbus-insertion distance may be another anatomic characteristic of PACG eyes.

Agreement between intraoperative measurements and optical coherence tomography of the limbus-insertion distance of the extraocular muscles

OBJECTIVE

To assess the agreement between intraoperative measurements of the limbus-insertion distance of the extraocular muscles with those measured by spectral domain optical coherence tomography.

METHODS

An analysis was made of a total of 67 muscles of 21 patients with strabismus. The limbus-insertion distance of the horizontal rectus muscles were measured using pre-operative SD-OCT and intra-operatively in 2 ways: 1) direct, after a conjunctival dissection in patients who underwent surgery, or 2) transconjunctival in patients who were treated with botulinum toxin, or in those who were not going to be operated. The intraclass correlation coefficient and Bland-Altman plots were calculated to determine the concordance between the 2 methods.

RESULTS

The mean age was 45.9 ±20.9 years (range 16 to 85), with 52% being women. The percentage of identification by direct intraoperative measurement was 95.6% (22/23), by transconjunctival intraoperative measurement 90.9% (40/44), and by OCT 85% (57/67), with 22 muscles finally being analysed for the agreement study between direct intraoperative measurement and OCT measurements, and 35 muscles for the agreement between transconjuctival intraoperative measurement and OCT. The intraclass correlation coefficient showed good agreement with OCT and direct intraoperative measurements (0.931; 95% confidence interval (95% CI): 0.839-0.972; P<.001), and with transconjunctival intraoperative measurements (0.889; 95% CI: 0.790-0.942; P<.001).

CONCLUSIONS

The SD-OCT is an effective technique to measure the distance from the insertion of the horizontal rectus muscles to the limbus, with a high agreement with intraoperative measurements being demonstrated.

Anterior Segment Optical Coherence Tomography of the Horizontal and Vertical Extraocular Muscles With Measurement of the Insertion to Limbus Distance

PURPOSE

To assess the possibility of determining the insertion distance from the limbus of horizontal and vertical extraocular rectus muscles with anterior segment optical coherence tomography (AS-OCT).

METHODS

The right eyes of 46 patients underwent AS-OCT. The horizontal and vertical extraocular rectus muscle insertion distances from the limbus were measured in a masked fashion by two pediatric ophthalmologists.

RESULTS

Forty-two lateral rectus, 43 medial rectus, 35 inferior rectus, and 40 superior rectus muscles of the right eyes of 46 patients were included. Insertion to limbus measurements (mean ± SD) were as follows: lateral rectus = mean 6.8 ± 0.7 mm, range = 4.8 to 8.4 mm; medial rectus = mean 5.7 ± 0.8 mm, range = 4.3 to 7.8 mm; inferior rectus = mean 6.0 ± 0.6 mm, range = 4.8 to 7.0 mm; superior rectus = mean 6.8 ± 0.6 mm, range = 5.5 to 8.1 mm. The intraobserver and interobserver correlation coefficients for the insertion to limbus measurements of all four rectus muscles exceeded 0.75 (excellent correlation).

CONCLUSIONS

The study showed that AS-OCT is capable of imaging all four of the rectus muscle insertions and measuring the insertion to limbus distance, and is the second AS-OCT study to image the superior and inferior rectus muscle insertions. The insertion to limbus measurements between examiners and on repeat measurements were consistent and reproducible. The ability to accurately image extraocular rectus muscle insertions may have future implications for the preoperative procedure planning in patients who have had previous surgery. [J Pediatr Ophthalmol Strabismus. 2016;53(3):141-145.].

Reproducibility of horizontal extraocular muscle insertion distance in anterior segment optical coherence tomography and the effect of head position

PURPOSE

To investigate the reproducibility of horizontal extraocular muscle insertion distance measurements in anterior segment optical coherence tomography (AS-OCT) and to evaluate the effect of eye position on the measurement.

METHODS

The right eyes of 30 healthy young subjects underwent AS-OCT. Varying eye positions were used and the muscle insertion distance was measured by two independent examiners who each measured the insertion distance twice. The measurement was performed for the lateral rectus and medial rectus muscles with the eye rotated 40°, 50°, and 60° to the midline of the instrument. Reproducibility was evaluated with the intraclass correlation coefficient (ICC) and Bland-Altman plot.

RESULTS

The lateral rectus insertion distance was smallest with 50° rotation and the medial rectus insertion distance did not show a consistent pattern in regards to gaze position. The differences in insertion distance between different eye positions were not statistically significant for both muscles. The inter- and intraexaminer ICC reproducibility values were excellent for both lateral and medial rectus insertion distance measurements.

CONCLUSIONS

Inter- and intraexaminer reproducibility were excellent for lateral and medial rectus muscle insertion distance measurements using AS-OCT. The measurements tended to be smallest with the 50° position in lateral rectus measurement; however, medial rectus measurements were variable.