Imaging anatomy and pathology of extraocular muscles in adults

Surgical management of unilateral restrictive strabismus in an 8-month-old dog

CASE HISTORY

An 8-month-old male, entire, mixed-breed dog was presented with a 1-month history of left exophthalmos and green mucopurulent ocular discharge. Subsequently, exophthalmos resolved but esotropia (medial strabismus) developed in the left eye, prompting referral to an ophthalmologist.

CLINICAL FINDINGS

At the initial referral consultation, enophthalmos and esotropia of the left eye were identified. The patient showed mild improvement after a 3-week tapering course of oral prednisolone and doxycycline. MRI was performed and showed left medial rectus muscle atrophy with increased contrast enhancement which was consistent with chronic extraocular muscle myositis (EOM). A forced duction test was performed to confirm the diagnosis of fibrosing esotropia, which is likely a sequela of chronic EOM.

DIAGNOSIS

Fibrosing esotropia presumably caused by untreated EOM.

TREATMENT AND OUTCOME

One month later, esotropia progressed to a marked ventro-medial strabismus resulting in visual deprivation. Surgical release of the ventral oblique, medial and ventral recti muscles was performed, resulting in immediate resolution of the enophthalmos. Despite a tapering post-operative course of oral prednisolone, mild esotropia was present 4 weeks later. In an effort to stabilise the globe position, the low dose of prednisolone was increased to a higher anti-inflammatory dose before slowly tapering over 2 months. The vision in the left eye was improved after surgery and has been maintained since without further treatment.

CLINICAL RELEVANCE

This is the first documented case of fibrosing esotropia in a young dog with prior signs of acute exophthalmos. Fibrosing esotropia has been documented in certain breeds or as a sequela to chronic EOM. In this patient, it was presumably caused by EOM, which was strongly supported by the case history, progression and MRI findings. Most historical reports of EOM described it as a bilateral condition that resolves with systemic corticosteroids at an anti-inflammatory dose. EOM has been shown to also present unilaterally and it can progress to strabismus if not promptly recognised and treated with systemic steroids. Surgical management can restore vision when severe strabismus results in visual deprivation.

Topographical anatomy of the annulus of Zinn

The anatomy and even existence of a common tendinous origin of the extraocular eye muscles, or annulus of Zinn, has widely been debated in anatomical literature. This study explored the anatomical origins of the recti muscles, their course into the orbit and the dural connections of the common tendinous origin with the skull base. Twenty orbits of ten adult human cadavers were dissected. The orbital apex and its dural connections were photographed. Histological examination of apical specimens was performed. In all cadavers, extraocular muscles were observed to have a common tendinous origin at the orbital apex, continuous with dural connections extending into the skull base. Accessory slips of the medial rectus were observed across all cadavers. Dual heads of the lateral rectus were observed in fourteen orbits of seven cadavers. The origin of the levator palpebrae superioris appeared to be contiguous with the superior rectus at the common tendinous origin in all but one cadaver. These results support the existence of a common tendinous origin of the extraocular muscles, that is continuous with the skull base dura. In addition, they support the existence of variations in orbital anatomy including dual or accessory muscle slips of the extraocular muscles.

Levator palpabrae superioris myositis as an unusual cause of unilateral ptosis—case report

Background

Ptosis can be a manifestation of a more serious situation. Hence, the analysis of the complaint and the search for etiology are crucial in such cases. Ptosis has many causes; some of them lead to unilateral ptosis while others cause bilateral ptosis. For instance, myasthenia gravis is a cause of bilateral ptosis while oculomotor nerve palsy induces unilateral disease. Proper evaluation of the patient and identification of the cause are important to achieve accurate management and good prognosis.

Case presentation

A 47-year-old male patient attended the ER complaining of dropping the right eye lid of 2 days’ duration. There was no associated pain or diplopia. On examination, the extraocular muscles’ (EOM) motility was intact, normal pupil and corneal reflexes, and there was swelling of the upper eyelid. Ophthalmological examination revealed normal anterior and posterior chambers as well as the vitreous and retina. The patient had a previous history of traumatic intracranial hemorrhage that was resolved without surgical intervention. He also had diabetes mellitus and hypertension. The patient was transferred to the MRI unit to perform MRI study of the brain and orbit with MRA and IV contrast administration. MRI findings confirmed the diagnosis of LPS myositis, and the patient received medical treatment and improved.

Conclusion

Proper radiological diagnosis leads to accurate management and achieves rapid recovery and optimal patient care.

Mass Spectrometric Profiling of Extraocular Muscle and Proteomic Adaptations in the mdx-4cv Model of Duchenne Muscular Dystrophy

Extraocular muscles (EOMs) represent a specialized type of contractile tissue with unique cellular, physiological, and biochemical properties. In Duchenne muscular dystrophy, EOMs stay functionally unaffected in the course of disease progression. Therefore, it was of interest to determine their proteomic profile in dystrophinopathy. The proteomic survey of wild type mice and the dystrophic mdx-4cv model revealed a broad spectrum of sarcomere-associated proteoforms, including components of the thick filament, thin filament, M-band and Z-disk, as well as a variety of muscle-specific markers. Interestingly, the mass spectrometric analysis revealed unusual expression levels of contractile proteins, especially isoforms of myosin heavy chain. As compared to diaphragm muscle, both proteomics and immunoblotting established isoform MyHC14 as a new potential marker in wild type EOMs, in addition to the previously identified isoforms MyHC13 and MyHC15. Comparative proteomics was employed to establish alterations in the protein expression profile between normal EOMs and dystrophin-lacking EOMs. The analysis of mdx-4cv EOMs identified elevated levels of glycolytic enzymes and molecular chaperones, as well as decreases in mitochondrial enzymes. These findings suggest a process of adaptation in dystrophin-deficient EOMs via a bioenergetic shift to more glycolytic metabolism, as well as an efficient cellular stress response in EOMs in dystrophinopathy.

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.

Neuroradiological and clinical features in ophthalmoplegia

PURPOSE

Especially in acute onset of ophthalmoplegia, efficient neuroradiological evaluation is necessary to assist differential diagnosis, clinical course, and treatment options.

METHODS

Different manifestations of ophthalmoplegia are explained and illustrated by characteristic neuroradiological and clinical findings.

RESULTS

To present those ophthalmoplegic disorders in a clear manner, this review refers to different neuroanatomical structures and compartments. From neuroophthalmological point of view, diseases going ahead with ophthalmoplegia can be divided into (1) efferent infranuclear/peripheral disturbances involving oculomotor cranial nerves, (2) conjugate gaze abnormalities due to internuclear or supranuclear lesions, and (3) diseases of the extraocular eye muscles or their impairment due to intraorbital pathologies.

CONCLUSION

The knowledge of the relationship between neurological findings in ophthalmoplegia and involved neuroanatomical structures is crucial, and neuroradiology can be focused on circumscribed anatomical regions, using optimized investigation protocols.

Horizontal Extraocular Muscle and Scleral Anatomy in Children: A Swept-Source Anterior Segment Optical Coherence Tomography Study

PURPOSE

To evaluate the efficacy of anterior segment swept-source optical coherence tomography (SS-OCT) for examining horizontal extraocular muscle thickness, distance from the corneal limbus to the insertion of the horizontal extraocular muscle (limbus to insertion distance), and scleral thickness in Korean pediatric strabismus patients.

METHODS

This study included pediatric strabismus patients between 5 and 10 years of age. Children with any ocular disease other than strabismus or a history of ocular surgery were excluded. SS-OCT was used to measure horizontal extraocular muscle thickness, limbus to insertion distance, and scleral thickness. Eyes were classified into subgroups by sex, spherical equivalent of the refractive error (measured with cycloplegic refraction), and fixating/deviating eye.

RESULTS

One patient initially included in this study was excluded due to poor cooperation. Of the remaining 35 eyes of 20 patients, 19 eyes (54.3%) were from male patients and 16 eyes (45.7%) were from female patients. The mean patient age was 7.86 ± 1.38 years. Lateral scleral thickness was greater in male eyes than in female eyes (p = 0.048). No other differences were noted between male and female children. Additionally, there were no statistically significant differences between fixating and deviating eyes or among spherical equivalent groups for any parameter examined.

CONCLUSIONS

Anterior segment SS-OCT can successfully and comfortably measure horizontal extraocular muscle and scleral anatomy in children. These measurements may be helpful for treatment and follow-up of pediatric strabismus patients.

Assessment of extraocular muscle thickness and correlation study using optical coherence tomography

OBJECTIVE

To report reference values for the horizontal rectus muscles thickness using Spectral Domain optical coherence tomography (SD-OCT), and to evaluate whether there are any correlations between the muscle thickness and gender, age, or axial length (AL).

MATERIAL AND METHODS

A cross-sectional study was conducted on 131 right eyes of healthy subjects. The gender and age were recorded, and axial length was measured using an optical biometer. The medial rectus (MR) muscle thickness was measured at 7.2 and 9.2mm from the limbus, and the lateral rectus (LR) at 8.5 and 10.5mm from the limbus using OCT. A multivariate model was adjusted to determine whether gender, age, and axial length could have an impact on the muscle thickness.

RESULTS

Mean age was 43.3±20.9 years (range 6-86), and 59% were women. Mean AL was 24.9±2.7mm (range: 20.4-33.8). Mean thickness was 188.5±51.2μm (range 69-342) for the LR at 8.5 and 186.5±45.9μm (range 75-269) at 10.5mm, and for the MR, 158.1±39.1μm (range 69-273) at 7.2mm and 193.7±55.9μm (range 105-386) at 9.2mm. A correlation was observed between the AL and MR thickness (R=-.255; P=.023) while no correlation was observed for the LR (P≥0.203). No correlations were found between thickness and gender or thickness and age (P≥0.125).

CONCLUSIONS

The reference ranges of the horizontal rectus muscles thickness was described using SD-OCT, observing an association between the AL and the MR thickness.

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.

Spectral domain optical coherence tomography to assess the insertion of extraocular rectus muscles

PURPOSE

To determine the distance of the horizontal rectus muscle insertion to the limbus using spectral domain optical coherence tomography (SD-OCT) and to evaluate whether results are correlated with sex, age, or axial length.

METHODS

The right eyes of healthy, white subjects were imaged with SD-OCT. Subjects' sex and age were recorded, and axial length was measured using an optical biometer. The distance from the horizontal rectus insertion to the limbus was measured. The intraclass correlation coefficient (ICC) was used to assess the reproducibility of the measurements with a subset of images. A multivariate model was adjusted to analyze whether sex, age, and axial length was correlated with insertion distance.

RESULTS

A total of 187 right eyes were included. Mean participant age was 43.7 ± 22.1 years (range, 6-85). Of the 187 patients, 129 were female; 25 were children. Mean axial length was 23.9 ± 1.6 mm (range, 20.4-29.3). Mean rectus insertion distance to the limbus was 6.47 ± 0.52 mm (range, 5.2-7.6 mm) for the lateral rectus muscle and 5.22 ± 0.51 mm (range, 4.1-6.1 mm) for the medial rectus muscle. ICC was >0.87 for intra- and interobserver reproducibility. The insertion-limbus distance was correlated with sex, being greater in males (P = 0.040 for the lateral rectus muscle; P = 0.036 for medial rectus muscle). There was no correlation between this distance and axial length or age (P > 0.156).

CONCLUSIONS

In this study cohort, the insertion distance of the horizontal rectus muscles to the limbus on SD-OCT was greater in males than females; however, age and axial length were not correlated with insertion distance.