MRI evaluation of cranial nerve abnormalities and extraocular muscle fibrosis in duane retraction syndrome and congenital extraocular muscle fibrosis

PURPOSE

To investigate the alterations in extraocular muscles (EOMs) by magnetic resonance imaging (MRI) among patients diagnosed with Duane retraction yndrome (DRS) and congenital fibrosis of the extraocular muscles (CFEOM), who present with various cranial nerve anomalies in an attempt to enhance the clinical diagnostic process.

METHODS

A case-control study was conducted to evaluate 27 patients with DRS and 14 patients with CFEOM. All patients underwent MRI scans of the brainstem and orbital examination. Neurodevelopmental assessments were conducted through MRI, and maximum cross-sectional area and volumes of EOMs were obtained. Three types of models were constructed using machine learning decision tree algorithms based on EOMs to predict disease diagnosis, cranial nerve abnormalities, and clinical subtypes.

RESULTS

Patients with bilateral CN VI abnormalities had smaller volumes of LR, MR, and IR muscles compared to those with unilateral involvement (P < 0.05). Similarly, patients with CFEOM and unilateral third cranial nerve abnormalities had a smaller maximum cross-section of the affected eye's SR compared to the contralateral eye (P < 0.05). In patients with both CN III and CN VI abnormalities, the volume of SR was smaller than in patients with CN III abnormalities alone (P < 0.05). The prediction model using EOMs volume showed a diagnostic precision of 82.5% for clinical cases and 60.1% for predicting cranial nerve abnormalities. Nonetheless, the precision for identifying clinical subtypes was relatively modest, at only 41.7%.

CONCLUSION

The distinctive volumetric alterations in EOMs among individuals exhibiting distinct cranial nerve anomalies associated with DRS or CFEOM provide valuable diagnostic insights into to Congenital Cranial Neurodevelopmental Disorders (CCDDs). MRI analysis of EOMs should thus be regarded as a crucial diagnostic modality.

Impact of sphenoid trigone size and extraocular muscle thickness on the outcome of lateral wall orbital decompression for thyroid eye disease

BACKGROUND

To retrospectively review lateral wall orbital decompression for thyroid eye disease (TED) and to evaluate pre-operative CT scans to analyse the variation in proptosis reduction.

METHODS

Consecutive lateral wall orbital decompressions performed by a single surgeon were retrospectively reviewed. Pre-operative CT scan features and post-operative proptosis reduction were analysed. The sphenoid trigone cross-sectional areas were summed and multiplied by the slice thickness to yield bone volume. Cumulative extraocular muscle thickness was calculated by combining the maximum thickness of the four recti. "Trigone volume" and "cumulative muscle thickness" were correlated with proptosis reduction at 3 months post-surgery.

RESULTS

Out of 73 consecutive lateral wall orbital decompressions, 17 orbits had prior endonasal medial wall orbital decompression. In the remaining 56 orbits, the mean pre-operative and post-operative proptosis were 24.3 ± 1.6 mm and 20.9 ± 2.3 mm respectively. The proptosis reduction ranged from 1 to 7 mm (mean of 3.5 mm ± 1.3 (p < 0.001)). Mean sphenoid trigone volume was 895 ± 434.4 mm3. The mean cumulative muscle thickness was 20.4 ± 5 mm. The correlation coefficient between muscle thickness and proptosis reduction was - 0.3 and was statistically significant (p = 0.043). The correlation coefficient between sphenoidal trigone volume and proptosis reduction was 0.2 (p = 0.068). With a multivariate analysis, the coefficient of efficient of regression for muscle thickness was - 0.007 (p = 0.42) and the coefficient of regression for trigone volume was 0.0 (p = 0.046).

CONCLUSION

Proptosis reduction following lateral wall orbital decompression can be variable. Extraocular muscle thickness had a significant correlation with the outcome, with greater proptosis reduction in orbits with thin muscles. The sphenoidal trigone size had a weak correlation with decompression outcome.

New Multi-Parameters Combination of Technetium-99m-Diethylene-Triamine-Pentaacetate Orbital Single-Photon Emission Computed Tomography/Computed Tomography for the Evaluation of Graves' Orbitopathy Activity

PURPOSE

This study investigates the new combined parameters of 99mTc-DTPA orbital single-photon emission computed tomography/computed tomography (SPECT/CT) for the evaluation of Graves' orbitopathy (GO) activity.

METHODS

A retrospective analysis was performed on 41 patients. All the patients undergone the 99mTc-DTPA orbital SPECT/CT and were categorized into active and inactive group based on the standard combined by the clinical active score (CAS), magnet resonance imaging (MRI) and/or follow-up results. Quantitative parameters of lacrimal gland (LG) including the protruding degree of lacrimal gland herniation (LGH) and uptake ratios (URs) of region of interest (ROI) drawn on lacrimal gland and occipital bone. SPECT/CT reading results were based on visual analysis. Parameters were compared between the two groups and the diagnostic value on discrimination of GO activity was also evaluated.

RESULTS

All parameters of SPECT/CT for active GO groups were significantly higher than those of the inactive groups (p<.05). There were notable linear positive correlations between the assumption standard and readings as well as combination models 2 and 3 (r = .794, r = .772, r = .760, respectively). ROC analysis indicated that model 2 provided the highest diagnostic performance, exhibiting an area under the curve (AUC) of .947, a sensitivity of 92.7%, and a specificity of 88.6%.

CONCLUSIONS

The combined use of SPECT/CT reading results and DTPA uptake parameters of LG offers a more objective and precise evaluation of active GO. This study further recommends 99mTc-DTPA SPECT/CT might be serving as a supplementary beneficial approach for CAS in evaluating GO activity.

Extraocular muscle stem cells exhibit distinct cellular properties associated with non-muscle molecular signatures

Skeletal muscle stem cells (MuSCs) are recognised as functionally heterogeneous. Cranial MuSCs are reported to have greater proliferative and regenerative capacity when compared with those in the limb. A comprehensive understanding of the mechanisms underlying this functional heterogeneity is lacking. Here, we have used clonal analysis, live imaging and single cell transcriptomic analysis to identify crucial features that distinguish extraocular muscle (EOM) from limb muscle stem cell populations. A MyogeninntdTom reporter showed that the increased proliferation capacity of EOM MuSCs correlates with deferred differentiation and lower expression of the myogenic commitment gene Myod. Unexpectedly, EOM MuSCs activated in vitro expressed a large array of extracellular matrix components typical of mesenchymal non-muscle cells. Computational analysis underscored a distinct co-regulatory module, which is absent in limb MuSCs, as driver of these features. The EOM transcription factor network, with Foxc1 as key player, appears to be hardwired to EOM identity as it persists during growth, disease and in vitro after several passages. Our findings shed light on how high-performing MuSCs regulate myogenic commitment by remodelling their local environment and adopting properties not generally associated with myogenic cells.

Development of the extraocular muscles during the fetal period

PURPOSE

The aim of this study was to investigate the morphometric development of the extraocular muscles in the fetal period and to create a modified Tillaux spiral.

METHODS

We dissected 157 fetal eyes (82 right eyes, 75 left eyes) obtained from 79 fetuses (46 boys, 33 girls) between 13 and 40 weeks of gestation. The tendon widths of the extraocular muscles and the distances of the tendon attachment sites to the limbus were measured. Tillaux's modified spiral was created.

RESULTS

In addition to the rectus muscles, we added tendon widths and tendon-limbus distances of the upper (SO) and lower (IO) obliques to the modified Tillaux spiral. When tendon widths were compared between genders, no statistically significant difference was observed. When tendon widths were compared between the sides, it was determined that SO was more in the left eye, whereas other extraocular muscles were more in the right eye. There was no statistically significant difference between genders when the distances of tendon attachment sites to the limbus were compared. There was no statistically significant difference in SO and IO values between the sides. There was a statistically significant difference in the rectus muscles and this difference was found to be higher in the right eye.

CONCLUSION

We think that the findings obtained will contribute to disciplines such as fetopathology, obstetrics, ophthalmology and plastic surgery and to future studies on this subject.

Clinical significance of CTGF and Cry61 protein in extraocular muscles of strabismic patients

PURPOSE

To investigate the relationship between clinical features and protein amounts of Cysteine-rich 61 (Cyr61/CCN1) and connective tissue growth factor (CTGF/CCN2), which are vital components and regulators of the extracellular matrix in resected muscles from strabismus surgery.

METHODS

Strabismus patients who were diagnosed with horizontal concomitant strabismus or inferior oblique overaction (IOOA) and required extraocular muscles (EOMs) resection to correct eye position were included in this study. The protein amounts were measured by enzyme-linked immunosorbent assay (ELISA) in resected EOMs. Multivariable linear regression was used to investigate the associations, adjusting for gender, age (continuous), amblyopia, and disease duration.

RESULTS

A total of 141 muscles (including 38 lateral, 81 medial rectus, and 22 inferior oblique muscles) from 128 patients were collected in this study. The amount of Cry61 and CTGF per millimeter was significantly negatively associated with deviation angle in intermittent exotropia patients (Cry61: β, - 1.44; 95%CI, - 2.79 to - 0.10, p = 0.035; CTGF: β, - 3.14; 95%CI, - 5.06 to - 1.22, p = 0.002). The same relationship was also detected in the partially accommodative and non-accommodative esotropia patients, although it was not statistically significant (Cry61: β, - 2.40; 95%CI, - 5.05 to 0.24; p = 0.073; CTGF: β, - 3.47; 95%CI, - 9.18 to 2.87; p = 0.269). The amount of Cry61 and CTGF per millimeter showed significant associations with the degree of IOOA (p < 0.05).

CONCLUSIONS

Taken together, our results demonstrated a significant relationship between deviation angle and protein amount of Cry61 and CTGF and implied that Cry61 and CTGF may play important roles in modulation of EOM contractility, which provide new insights into strabismus pathogenesis.

Surgical and anesthetic influences of the oculocardiac reflex in adults and children during strabismus surgery

One of the most common untoward occurrences during strabismus surgery at all ages is the oculocardiac reflex. Although typically easily treated, the sudden bradycardia or cardiac arrest may add a few gray hairs to ophthalmologists and anesthesiologists alike as it can be potentially fatal. This updated review of the literature and novel detailed treatment algorithm may prevent patient morbidity and mortality through proper recognition of at-risk patients and rapid treatment through proper communication between surgical and anesthesia physicians/providers.

Dynamic Electrooculography Findings for Medial Rectus Myofascial Release in Esodeviation

Purpose

To determine which mechanisms are operative in releasing the extraocular myofascial tissue in response to extraocular myofascial release (EOMR) and to evaluate the effect of EOMR on saccadic velocity and esodeviation angle in patients with convergence spasm.

Methods

Fourteen patients with convergence spasm aged 20-35 participated in this research. The treatment included touching the medial rectus and its interrelated fascial tissue with the index finger pulp from over the eyelid for at least 300 s and applying very gentle and uniform pressure. We evaluated the saccadic velocity obtained from dynamic electrooculography (EOG) and the angle of deviation. The findings of dynamic EOG were used as a reliable quantitative method to assess eye movement function.

Results

The amount of esodeviation decreased significantly at both far 2.39Δ, 95% confidence interval (CI) (1.27-3.52) (P = 0.002) and near 5.57Δ, 95% CI (4.67-6.47) (P = 0.001) after two sessions of EOMR in a week. There was no significant difference in saccadic velocities before and after treatment.

Conclusion

In the short term, the EOMR only affects the static condition of the eye. Therefore, a significant improvement could be seen in the deviometric findings. However, the dynamic properties of the extraocular muscles did not improve and probably needed a more extended treatment period for acting the long-term mechanisms.

Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement-a narrative review

Strabismus is not a condition in itself but the consequence of an underlying problem. Eye misalignment can be caused by disease, injury, and/or abnormalities in any of the structures and processes involved in visual perception and oculomotor control, from the extraocular muscles and their innervations to the oculomotor and visual processing areas in the brain. A small percentage of all strabismus cases are the consequence of well-described genetic syndromes, acquired insult, or disease affecting the extraocular muscles (EOMs) or their innervations. We will refer to them as strabismus of peripheral origin since their etiology lies in the peripheral nervous system. However, in most strabismus cases, that is comitant, non-restrictive, non-paralytic strabismus, the EOMs and their innervations function properly. These cases are not related to specific syndromes and their precise causes remain poorly understood. They are generally believed to be caused by deficits in the central neural pathways involved in visual perception and oculomotor control. Therefore, we will refer to them as central strabismus. The goal of this narrative review is to discuss the possible causes behind this particular type of eye misalignment and to raise awareness among eyecare professionals about the important role the central nervous system plays in strabismus etiology, and the subsequent implications regarding its treatment. A non-systematic search was conducted using PubMed, Medline, Cochrane, and Google Scholar databases with the keywords "origins," "causes," and "etiology" combined with "strabismus." A snowball approach was also used to find relevant references. In the following article, we will first describe EOM integrity in central strabismus; next, we will address numerous reasons that support the idea of central nervous system (CNS) involvement in the origin of the deviation, followed by listing several possible central causes of the ocular misalignment. Finally, we will discuss the implications CNS etiology has on strabismus treatment.

Retinal and choroidal microvasculature is altered after strabismus surgery

PURPOSE

To evaluate the retinal and choroidal microvasculature after strabismus surgery using swept-source optical coherence tomography angiography (OCTA).

METHODS

Thirty-three eyes of 33 patients who underwent horizontal rectus surgery for strabismus were included in this retrospective study. The unoperated fellow eyes were used as the control group. The macular microvasculature was assessed using a 3 × 3 scan pattern centred on the fovea preoperatively, and one week and one month postoperatively. The vessel density (VD) of superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC) were automatically analyzed. The foveal avascular zone (FAZ) was calculated manually using the tool of the device.

RESULTS

The VD in SCP demonstrated a significant difference between operated and fellow eyes at one week (p = 0.017). Moreover, a significant increase was observed in the mean VD values in SCP of operated eyes after surgery (p = 0.037). The VD in DCP exhibited no significant differences between operated and fellow eyes before and after strabismus surgery. However, there was a significant difference in VD was observed between operated and fellow eyes one week after surgery (p = 0.001). The mean VD in CC was significantly increased in the operated eyes one week after surgery compared to preoperative values (p = 0.006).

CONCLUSION

This study revealed that strabismus surgery may cause transient alterations both in retinal and choroidal microcirculation in the early postoperative period.

TWIST1, a gene associated with Saethre-Chotzen syndrome, regulates extraocular muscle organization in mouse

Heterozygous loss of function mutations in TWIST1 cause Saethre-Chotzen syndrome, which is characterized by craniosynostosis, facial asymmetry, ptosis, strabismus, and distinctive ear appearance. Individuals with syndromic craniosynostosis have high rates of strabismus and ptosis, but the underlying pathology is unknown. Some individuals with syndromic craniosynostosis have been noted to have absence of individual extraocular muscles or abnormal insertions of the extraocular muscles on the globe. Using conditional knock-out alleles for Twist1 in cranial mesenchyme, we test the hypothesis that Twist1 is required for extraocular muscle organization and position, attachment to the globe, and/or innervation by the cranial nerves. We examined the extraocular muscles in conditional Twist1 knock-out animals using Twist2-cre and Pdgfrb-cre drivers. Both are expressed in cranial mesoderm and neural crest. Conditional inactivation of Twist1 using these drivers leads to disorganized extraocular muscles that cannot be reliably identified as specific muscles. Tendons do not form normally at the insertion and origin of these dysplastic muscles. Knock-out of Twist1 expression in tendon precursors, using scleraxis-cre, however, does not alter EOM organization. Furthermore, developing motor neurons, which do not express Twist1, display abnormal axonal trajectories in the orbit in the presence of dysplastic extraocular muscles. Strabismus in individuals with TWIST1 mutations may therefore be caused by abnormalities in extraocular muscle development and secondary abnormalities in innervation and tendon formation.

Is the central mesencephalic reticular formation a purely horizontal gaze center?

Historically, the central mesencephalic reticular formation has been regarded as a purely horizontal gaze center based on the fact that electrical stimulation of this region produces horizontal saccades, it provides monosynaptic input to medial rectus motoneurons, and cells recorded in this region often display a peak in firing when horizontal saccades are made. We tested the proposition that the central mesencephalic reticular formation is purely a horizontal gaze center by examining whether this region also supplies terminals to superior rectus and levator palpebrae superioris motoneurons, both of which fire when making vertical eye movements. The experiments were carried out using dual tracer techniques at the light and electron microscopic level in macaque monkeys. Injections of biotinylated dextran amine or Phaseolus vulgaris leukoagglutinin into the central mesencephalic reticular formation produced anterogradely labeled terminals that were in synaptic contact with superior rectus and levator palpebrae superioris motoneurons that had been retrogradely labeled. These results indicate that this region is not purely connected with horizontal gaze motoneurons. In addition, we found that the number of contacts on vertical gaze motoneurons increased with more rostral injections involving the mesencephalic reticular formation adjacent to the interstitial nucleus of Cajal. This suggests that there is a caudal to rostral gradient for horizontal to vertical saccades, respectively, represented within the midbrain reticular formation. Finally, we utilized post-embedding immunohistochemistry to show that a portion of the labeled terminals were GABAergic, indicating they likely originate from downgaze premotor neurons.

Role of muscle biopsy in diagnosis of extraocular muscles enlargement

PURPOSE

To study the role of muscle biopsy in patients with enlarged extraocular muscles.

METHODS

A retrospective review of 31 patients who underwent biopsy for extraocular muscle enlargement. Characteristics, including signs, symptoms, imaging findings, and histopathological assessment were examined.

RESULTS

Chronic inflammatory disorders represented the most common cause of the muscle enlargement followed by malignancy/metastasis. Multiple muscle involvement was more consistent with benign diseases, whereas single muscle involvement was more consistent with malignant causes. Positive predictive value of muscle biopsy was 0.52 for determining a specific cause of the muscle enlargement.

CONCLUSIONS

Muscle biopsy is the standard for diagnosis in patients with extraocular muscle enlargement. This diagnostic test should be performed in every case of non-resolving muscle enlargement, with a specific diagnosis being made in over half of cases.

Ocular hypertension in patients with active thyroid-associated orbitopathy: a predictor of disease severity, particularly of extraocular muscle enlargement

The purpose was to ascertain if any relation exists between the elevated intraocular pressure (IOP) in patients with thyroid-associated orbitopathy (TAO) in active stage and the severity of extraocular muscle involvement and the extent of exophthalmos.

METHODS

A total of 96 eyes and orbits of 48 adult patients with active TAO were investigated. All patients underwent magnetic resonance imaging of the orbit and measurement of all extraocular recti muscles (EOM). The obtained data was divided into two groups according to the IOP value: normal IOP ≤ 21 mmHg; n = 47 and elevated IOP with IOP > 21 mmHg; n = 49, and analyszed.

RESULTS

A significant difference was found in the short diameter of medial rectus and inferior rectus muscles and in the sum of short parameters of all EOM. All these parameters were significantly higher in the elevated IOP group. Motility restriction in at least one gaze direction was also significantly more frequent (p < 0.0001) in the elevated IOP group. A positive moderate correlation was found between IOP and the sum of short parameters of EOM (r = 0.496). No correlation was found between the IOP and exophthalmos values (r = 0.267). During the follow-up, the frequency of strabismus surgery and orbital decompression was significantly higher in the elevated IOP group (p = 0.003; p = 0.002).

CONCLUSION

Elevated IOP in the active TAO stage particularly correlates with extraocular muscle involvement. These patients are also more likely to require orbital decompression and strabismus surgery.

Monitoring surgery around the cranial nerves

Intraoperative neurophysiologic monitoring (IONM) of cranial nerve (CN) function is an essential component in multimodality monitoring of surgical procedures where CNs are at risk for injury. In most cases, IONM consists of localizing and mapping CNs and their pathways, and monitoring of CN motor function during surgery. However, CN VIII, which has no motor function, and is at risk for injury in many surgical procedures, can be easily and accurately monitored using brainstem auditory evoked potentials. For motor CNs, the literature is clear that function can be safely and adequately performed using basic electromyographic (EMG) techniques, such as recording of continuous EMG activity and electrically evoked compound muscle actions potentials. Newer techniques, such as corticobulbar motor evoked potentials and reflex studies, show good potential for a greater degree of functional assessment but require further study to determine their clinical utility. EMG remains the basic clinical neurophysiologic technique with the greatest clinical research supporting its utility in IONM of motor CN function and should be used as part of a comprehensive multimodality IONM protocol. Understanding the physiologic basis of EMG and the changes associated with altered motor function will allow the practitioner to alter surgical course to prevent injury and improve patient safety.

Tendinous annulus of Zinn for a common origin of the extraocular rectus muscles: a histological study of the orbital apex from donated elderly cadavers

The medial, inferior, lateral, and superior rectus muscles (MR, IR, LR, SR), levator palpebrae superioris (LPS), and superior oblique muscle (SO) seem to originate from the tendinous annulus of Zinn, ring-like fibrous tissue crossing the bony orbital fissure. We observed the histological annulus structure using semi-serial histological sections of the orbital apex from 30 elderly donated cadavers. Nearly frontal sections demonstrated a ring-like fibrous structure (a candidate annulus) connecting or embedding four rectus muscles. The candidate annulus did not contain the LPS and SO, and, in the anterior side, the latter muscles originated from the optic canal opening. Far posterior to the annulus, there was a common tendon of the MR, IR, and LR attached to the infero-medial wall of the bony orbital fissure. At the superior part, the annulus is tightly attached to the optic nerve sheath and the periosteum. Sagittal (or Horizontal) sections clearly exhibited parts of the annulus at the MR (SR) origin. Both sagittal and horizontal sections displayed (1) the common origin of the three rectus muscles near the oculomotor nerve in the bony fissure and (2) an accessory, independent muscle bundle of the MR originating from the superomedial margin of the optic canal near the origins of the LPS or SO. Consequently, the so-called tendinous annulus appeared not to provide origins of all six muscles.

Correlation between extent of lacrimal gland prolapse and clinical features of thyroid-associated ophthalmopathy: a retrospective observational study

Background

Studies on the factors related to lacrimal gland prolapse (LGP) in patients with thyroid-associated ophthalmopathy (TAO) are limited. This study aimed to assess the factors associated with LGP on magnetic resonance imaging (MRI) and its relation to TAO activity .

Methods

Thirty-six patients (72 orbits) with inactive TAO (43 orbits, Clinical Activity Score [CAS] < 3) or active TAO (29 orbits, CAS ≥3) were investigated retrospectively. All patients underwent ophthalmic evaluation and orbital magnetic resonance imaging. The severity of LGP and proptosis and the extraocular muscle (EOM) volume were measured. LGP and related factors were assessed by correlational and linear regression analyses. The value of LGP for discriminating the activity of TAO was evaluated by receiver-operating characteristic curve analysis.

Results

The mean LGP was significantly higher in the active TAO group than in the inactive TAO group (P < 0.001). There were significant positive correlations between LGP severity and the CAS (r = 0.51, P < 0.001), proptosis (r = 0.72, P < 0.001), and EOM volume (superior rectus [r = 0.49, P < 0.001], inferior rectus [r = 0.47, P < 0.001], lateral rectus [r = 0.59, P < 0.001], medial rectus [r = 0.62, P < 0.001], superior oblique [r = 0.48, P < 0.001], and all EOMs [r = 0.59, P < 0.001]). Receiver-operating characteristic curve analysis revealed an LGP of 13.65 mm (area under the curve, 0.824; sensitivity, 79.3%; specificity, 81.4%) to be the cut-off value that differentiated active and inactive TAO.

Conclusions

LGP measurements obtained from orbital magnetic resonance images were positively correlated with CAS, proptosis and EOM volume. The extent of LGP appears to be a good indicator of disease activity in patients with TAO.

Evaluation of the insertion distance of the medial rectus in consecutive exotropia by means of intraoperative measure and optical coherence tomography

PURPOSE

To assess the agreement between the measurements of the distance from the medial rectus muscles insertion to the limbus measured by intra-operative spectral-domain optical coherence tomography (SD-OCT) in consecutive exotropia (cXT).

METHODS

An analysis was performed on total of 14 medial rectus (MR) muscles of 14 patients who underwent surgery for the treatment of cXT. The limbus-insertion distance of the MR muscles was measured using preoperative SD-OCT and intraoperatively using a calliper. The intraclass correlation coefficient (ICC) and Bland Altman plots were calculated to determine the agreement between the two methods, as well as the correlation.

RESULTS

Mean age was 36.3 ± 16.0 years (range 13-60), with 60% being women. Mean preoperative deviation was 38.7 ± 16.9 prismatic dioptres (PD) (range 16-65), being +1.3 ± 6.3 PD (range -12 to +10 PD) after surgery. Intraoperatively the MR insertion was found at 8.7 ± 2.1 mm (range 5.5-12.0) and by OCT at 7.7 ± 1.2 mm (range 5.3-10.0). The ICC showed a moderate to good agreement (0.659; 95% confidence interval: 0.157-0.885; p < 0.001), with a correlation of R = 0.792 (p = 0.011). A better agreement was observed in those MR that were less retro-inserted.

CONCLUSIONS

SD-OCT is able to measure the insertion to the limbus distance of the medial rectus muscles that have been previously operated on, showing moderate to good agreement with intraoperative measurements. However, the agreement was poor in muscles with a large retro-insertion.

Age-related difference in extraocular muscles and its relation to clinical manifestations in an ethnically homogenous group of patients with Graves' orbitopathy

PURPOSE

To evaluate the age-related difference in EOMs and its relation to clinical manifestations by computed tomography (CT) measurement of EOMs.

METHODS

The medical records and CT image review of 40 patients (80 orbits) with moderate-to-severe Graves' orbitopathy were performed. The patients were divided into two age groups, group 1 (≤ 40 years) and group 2 (> 40 years). CT scans of 30 gender- and age-matched normal controls were also obtained. The maximal cross-sectional area (MCA) and its position (pMCA) of each EOM were measured.

RESULTS

Group 1 presented with more severe proptosis (p < 0.001), while group 2 had a higher risk of diplopia (p < 0.001). Motility restriction in supraduction was more likely to occur in Group 2 (p = 0.027) with even higher severity (p = 0.047). The pMCA was higher in the inferior (p = 0.001), medial (p = 0.021), and lateral rectus (p = 0.013) in group 1. Proptosis was positively correlated to pMCA while diplopia was correlated to MCA in both groups. Significant correlation was noted between restrictions levels and MCA (superior, r = 0.467, p < 0.001; inferior, r = 0.358, p = 0.007; medial, r = 0.314, p = 0.018; lateral, r = 0.308, p = 0.021) or pMCA (inferior, r =  - 0.534, p < 0.001) only in group 2.

CONCLUSIONS

The muscle enlargement patterns are significantly different between younger and older patients. Older patients tended to have enlarged muscle bellies more posterior in the orbit, which is responsible for more diplopia and motility restriction. Proptosis is more likely to be affected by the most enlarged position than muscle size. So younger patients tended to develop more proptosis and be less bothered by motility restriction even with enlarged muscles.

Extrathyroidal Manifestations of Thyroid Disease: Graves Eye Disease

Graves disease is an autoimmune disorder caused by the breakdown of immune tolerance to thyroid antigens against the TSH receptor. In approximately 25% of patients, an inflammatory condition, Graves eye disease (GED), affects the orbital soft tissues. About 60% of patients develop mild symptoms including fat expansion and inflammation of the levator muscle complex with resultant proptosis, eyelid retraction, and exposure of the globe. The remaining patients experience enlargement of one or more of the extraocular muscles, leading to conjunctival and eyelid edema and congestion, restricted ocular movement with resultant diplopia, and optic nerve compression leading to compressive optic neuropathy.

MRI evidence of extraocular muscle atrophy and fatty replacement in myasthenia gravis

PURPOSE

The aim of the study was to evaluate extraocular muscle (EOM) atrophy and fatty replacement in ocular myasthenia gravis (OMG) and generalized myasthenia gravis (GMG) patients with chronic and untreated ocular symptoms or with inadequate response to immunotherapy and unprovoked ocular exacerbations despite chronic immunotherapy.

METHODS

Nineteen patients with either OMG or GMG and 19 healthy age-matched controls underwent an orbital MRI. Visually obvious muscle atrophy and muscle fatty replacement were evaluated by two raters independently. Maximum thickness of EOM was measured. Measurements of the muscles of each participant were added up, in order to calculate the total thickness.

RESULTS

Eleven patients suffered from AChR-positive GMG, and 8 patients from OMG. All patients had chronic ocular symptoms or inadequate response to corticosteroids and unprovoked ocular exacerbations in spite of immunotherapy. Fatty replacement was reported in 6/19 (31.6%) patients and 0/19 (0%) controls (p = 0.02). Obvious atrophy in at least one muscle was reported in 8/19 (42.1%) patients and 1/19 (5.3%) controls (p = 0.019). Statistically significant differences between the two groups were also found in the mean total thickness, as well as in the thickness of superior recti, levator palpebrae, inferior recti, and superior oblique muscles.

CONCLUSION

EOM atrophy and fatty replacement were seen frequently in our series of MG patients with treatment difficulties and frequent relapses of ocular involvement.

Sliding shape extraocular muscle transposition with plication: Long-term results

AIM

This study aims to evaluate the long-term results of sliding shape extraocular muscle transposition, which is a novel operation method of delivering both vascular protection and strengthening of the muscles and transposition of the muscles.

METHODS

The patients' files were scanned retrospectively. All patients underwent a complete eye examination in addition to motility examination, both preoperatively and postoperatively. Patients were followed up for at least 1 year. Pre- and postoperative deviation measurement values and transposition effects were compared statistically. The two parameters were evaluated separately.

RESULTS

In patients where 7-mm (or greater) resection was planned, the complete muscle widening transposition procedure was successful. Only two-thirds of transpositions could be achieved in patients who underwent less than 7 mm of strengthening. There was no anterior segment ischemia in the patients who underwent three rectus' muscle surgery in the same eye. Transposition effects were perfect in those whose vertical deviation was not due to monocular elevation deficiency. While resection effect was excellent in those MED (monocular elevation deficiency) and CEOMF (congenital extraocular muscle fibrosis) cases, transposition effects were limited but found at similar rates as with the standard resection and transposition procedures in CCDD (congenital cranial dis-innervation diseases) (R2-1).

CONCLUSION

Even transposition effects were limited in CCDD. 'Sliding shape' design extraocular muscle plication was found to be a simple, safe, and effective procedure for patients who needed resection and transposition operation.

[Clinical Analysis of 2 170 Cases of Thyroid-Associated Ophthalmopathy Involving Extraocular Muscles]

OBJECTIVE

To explore the clinical features of thyroid-associated ophthalmopathy (TAO) with extraocular muscle involvement.

METHODS

The data of 2170 TAO patients who were seen at the Orbital Disease Clinic, West China Hospital, Sichuan University from September, 2009 to January, 2020 were collected retrospectively. The extraocular muscle involvement of these patients was confirmed by CT or MRI. Their general condition, medical history, clinical manifestations and imaging features were analyzed retrospectively.

RESULTS

Among the 2170 TAO patients, 932 were male and 1238 were female. The mean (± SD) age of all the patients was (46.95±13.06) years, ranging between 6 and 85. 1684 patients (77.60%) suffered from hyperthyroidism, 13 patients (0.59%) had thyroid cancer, 80 patients (3.69%) had hypothyroidism, and 393 patients (18.11%) had normal thyroid function. Proptosis (55.25%) and diplopia (33.09%) were the main reasons for their visits to the clinic, and restricted eye movements (83.46%) was the most common sign. 122 patients with a mean age of (53.24±13.07) years did not show any eyelid sign and had only extraocular muscle involvement. The 2170 TAO patients had a total of 3799 eyes of extrocular muscle involvement, with 541 patients experiencing monocular involvement and 1629 patients, binocular involvement; 1204 eyes (31.69%) had a single extrocular muscle involved and 2595 eyes (68.31%) had multiple extrocular muscles involved. Inferior rectus was the most commonly involved muscle, followed by superior rectus, medial rectus, and lateral rectus in descending order of involvement frequency. Of the 1014 patients who underwent enhanced MRI, 71.99% were shown to be in the active phase. 69.03% of the 775 patients identified as being in inactive phase according to their clinical activity score (CAS) were shown to be in the active phase according to their MRI results.

CONCLUSION

TAO patients with extraocular muscle involvement have their own specific clinical manifestations. CT and MRI can both be used to assist in the diagnosis of extraocular muscle involvement. MRI can be used to assess the pathological stage of extraocular muscles and is more sensitive than CAS.

Developmental fates of shark head cavities reveal mesodermal contributions to tendon progenitor cells in extraocular muscles

Vertebrate extraocular muscles (EOMs) function in eye movements. The EOMs of modern jawed vertebrates consist primarily of four recti and two oblique muscles innervated by three cranial nerves. The developmental mechanisms underlying the establishment of this complex and the evolutionarily conserved pattern of EOMs are unknown. Chondrichthyan early embryos develop three pairs of overt epithelial coeloms called head cavities (HCs) in the head mesoderm, and each HC is believed to differentiate into a discrete subset of EOMs. However, no direct evidence of these cell fates has been provided due to the technical difficulty of lineage tracing experiments in chondrichthyans. Here, we set up an in ovo manipulation system for embryos of the cloudy catshark Scyliorhinus torazame and labeled the epithelial cells of each HC with lipophilic fluorescent dyes. This experimental system allowed us to trace the cell lineage of EOMs with the highest degree of detail and reproducibility to date. We confirmed that the HCs are indeed primordia of EOMs but showed that the morphological pattern of shark EOMs is not solely dependent on the early pattern of the head mesoderm, which transiently appears as tripartite HCs along the simple anteroposterior axis. Moreover, we found that one of the HCs gives rise to tendon progenitor cells of the EOMs, which is an exceptional condition in our previous understanding of head muscles; the tendons associated with head muscles have generally been supposed to be derived from cranial neural crest (CNC) cells, another source of vertebrate head mesenchyme. Based on interspecies comparisons, the developmental environment is suggested to be significantly different between the two ends of the rectus muscles, and this difference is suggested to be evolutionarily conserved in jawed vertebrates. We propose that the mesenchymal interface (head mesoderm vs CNC) in the environment of developing EOM is required to determine the processes of the proximodistal axis of rectus components of EOMs.

Quantitative measurement of passive duction force tension in intermittent exotropia and its clinical implications

PURPOSE

To evaluate the passive duction force (PDF) in extraocular muscles (EOMs) in patients with intermittent exotropia (IXT) using a quantitative tension-measuring device.

METHODS

This prospective, case-control study enrolled 25 patients with IXT and 26 age- and sex-matched controls. PDF was measured under general anesthesia as the eyeball was rotated medially or laterally away from the direction of the force being tested. The preferred eye for fixation was determined using a cover-uncover test.

RESULTS

The PDF in the IXT and control groups were 60.9 g and 52.1 g, respectively, for the lateral rectus (LR) (p = 0.046) and 53.0 g and 48.8 g for the medial rectus (MR) (p = 0.293). When the eyes were examined separately in the IXT group, the PDF of LR was larger in the nonpreferred eye for fixation than in the control group (p = 0.039), whereas there was no difference in the preferred eye for fixation (p = 0.216). Additionally, the relative PDF of LR in the nonpreferred eye compared to the ipsilateral PDF of MR was positively associated with the duration of manifest deviation (p = 0.042) and the average angle of the near and far deviations (p = 0.023).

CONCLUSIONS

The PDF in the LR in patients with IXT in the nonpreferred eye for fixation was larger than normal and could increase with the duration of manifest deviation and the angle of deviation. Evaluating the PDF in EOMs could provide information that is useful for managing strabismus and understanding its pathophysiology.

Evaluation of the insertion distance of the medial rectus in consecutive exotropia by means of intraoperative measure and optical coherence tomography

PURPOSE

To assess the agreement between the intraoperative measurements of the distance from the medial rectus muscles insertion to the limbus and preoperative spectral-domain optical coherence tomography (SD-OCT) in consecutive exotropia (cXT).

METHODS

An analysis was performed on total of 14 medial rectus (MR) muscles of 14 patients who underwent surgery for the treatment of cXT. The limbus-insertion distance of the MR muscles was measured using preoperative SD-OCT and intraoperatively using a calliper. The intraclass correlation coefficient (ICC) and Bland Altman plots were calculated to determine the agreement between the two methods, as well as the correlation.

RESULTS

Mean age was 36.3±16.0 years (range 13-60), with 60% being women. Mean preoperative deviation was 38.7±16.9 prismatic dioptres (PD) (range 16 to 65), being +1.3±6.3 PD (range -12 to +10 PD) after surgery. Intraoperatively the MR insertion was found at 8.7±2.1mm (range 5.5 - 12.0) and by OCT at 7.7±1.2mm (range 5.3 - 10.0). The ICC showed a moderate to good agreement (0.659; 95% confidence interval: 0.157-0.885; P<.001), with a correlation of R=0.792 (P=.011). A better agreement was observed in those MR that were less retro-inserted.

CONCLUSIONS

SD-OCT is able to measure the insertion to the limbus distance of the medial rectus muscles that have been previously operated on, showing moderate to good agreement with intraoperative measurements. However, the agreement was poor in muscles with a large retro-insertion.

Gene expression profiling of orbital muscles in treatment-resistant ophthalmoplegic myasthenia gravis

Background

Unbiased in silico approaches applied to genome-wide data prioritized putative functional gene variants associating with treatment-resistant ophthalmoplegic myasthenia gravis (OP-MG). Although altered expression of genes harbouring these variants, or associated pathways, were shown in patient-derived transdifferentiated-myocyte models, gene expression in orbital-derived muscle was required to test the validity of the predictions.

Methods

We sampled orbicularis oculi muscle (OOM) and one paralysed extraocular muscle (EOM) from six individuals with OP-MG during blepharoptosis and re-alignment surgeries, respectively. For controls, the OOMs were sampled from four individuals without myasthenia undergoing surgery for non-muscle causes of ptosis, and one non-paralysed EOM. Using a qPCR array, expression of 120 genes was compared between OP-MG and control OOMs, profiling putative “OP-MG” genes, genes in related biological pathways and genes reported to be dysregulated in MG cases or experimental MG models, and in EOMs of cases with strabismus. Normalization was performed with two stable reference genes. Differential gene expression was compared between OP-MG and control samples using the ΔΔCT method. Co-expression was analysed by pairwise correlation of gene transcripts to infer expression networks.

Results

Overall, transcript levels were similar in OOMs and EOMs (p = 0.72). In OOMs, significant downregulated expression of eight genes was observed in OP-MG cases compared with controls (> twofold; p ≤ 0.016), including TFAM, a mitochondrial transcription factor, and genes related to the following pathways: atrophy signalling; muscle regeneration and contraction; glycogen synthesis; and extracellular matrix remodelling. Several microRNAs, known to be highly expressed in EOMs, are predicted to regulate some of these genes. Co-expression analyses of gene-pairs suggested high interconnectedness of gene expression networks in OP-MG muscle, but not controls (r > 0.96, p < 0.01). Significant inverse directions of gene-pair correlations were noted in OP-MG versus controls OOM networks (r ≥ 0.92, p < 0.001) involving most OP-MG genes overlapping prominently with muscle atrophy/contractility and oxidative metabolism genes.

Conclusions

The gene expression in orbital muscles derived from OP-MG individuals compared with normal controls, support the pathogenic hypothesis previously generated from whole genome sequence analyses. Repression of gene transcripts in OP-MG orbital muscle implicate tissue-specific regulatory mechanisms, which may inform future biomarker discovery approaches.

Imaging of congenital cranial dysinnervation disorders: What radiologist wants to know?

We aim to review the imaging features of congenital cranial dysinnervation disorders. Characteristic imaging findings can define subtypes of these disorders through assessment of cranial nerves, extraocular muscles, orbital, and brain abnormalities. Duane retraction syndrome shows absent or hypoplasic 6th cranial nerve and preserved extraocular muscles (EOM). Mobius syndrome shows absent 7th and 6th cranial nerves, absence of facial colliculus, flattening of the dorsal aspect of the pons, hypoplasia of the pons and medulla, and flattening of the 4th ventricular floor. Congenital fibrosis of the extraocular muscles reveals unilateral or bilateral hypoplasia or aplasia of the 3rd cranial nerve, atrophy of superior rectus and levator palpebrae superioris muscles, and atrophy of the brainstem and cerebellar hemispheres. Horizontal gaze palsy and progressive scoliosis show characteristic split pons sign, butterfly medulla, absent facial colliculi, and spinal scoliosis. HOXA1 Mutations show a bilateral absence of 6th cranial nerves with the underdeveloped inner ear. Pontine Cap Tegmental Dysplasia shows ventral pontine hypoplasia, dorsal tegmental projection into the 4th ventricle, and variable cranial nerve deficits.

T2 mapping of the extraocular muscles in healthy volunteers: preliminary research on scan-rescan and observer-observer reproducibility

BACKGROUND

T2-mapping technique and derived T2 relaxation time allows quantitative assessment of extraocular muscles; however, the reproducibility of T2 mapping-derived parameters was seldom studied till now.

PURPOSE

To evaluate the scan-rescan and observer-observer reproducibility of T2 relaxation time measurements of extraocular muscles in young healthy volunteers.

MATERIAL AND METHODS

Fourteen volunteers underwent T2-mapping examinations of the extraocular muscles three times within one month on a 3.0-T MR system. Scan-rescan and observer-observer reproducibility of T2 relaxation time measurements of the extraocular muscles were assessed using intraclass correlation coefficient and coefficient of variation.

RESULTS

Both scan-rescan (short-term and long-term) and observer-observer could achieve good to excellent reproducibility, while better short-term than long-term scan-rescan reproducibility was obtained. The coefficient of variation of the T2 relaxation time of each extraocular muscles during both scan-rescan and observer-observer reproducibility assessment were <6%.

CONCLUSION

T2 relaxation time measurement of the extraocular muscles is proven to be highly reproducible at 3.0 T. T2 mapping may be a potential imaging technique in the diagnosis and follow-up of orbital diseases involved extraocular muscles in further studies.

The "Crab" Memory Tool for the Actions of the Extraocular Muscles

INTRODUCTION

Understanding the primary, secondary and tertiary actions of the vertical recti and oblique muscles is important in the diagnosis of various types of strabismus (superior oblique palsy, A- and V-patterns). Unfortunately, learning these actions can be very challenging. We designed a visual memory tool, and assessed its usefulness for medical students.

METHODS

Medical students undergoing their rotation in ophthalmology were taught the actions of the extraocular muscles either without the memory aid (control group) or with it (test group). The students were surveyed one week and one month later to determine their ability to recall the muscle actions and asked to subjectively rate the usefulness of the memory aid.

RESULTS

Approximately 40% of the test group used the memory tool. Eighty-seven percent of the respondents recommended that the memory aid be taught in the future. Overall, there was no significant difference in the ability to recall the actions of the muscles between the control and test groups. However, those students who found the memory aid helpful had significantly better recall than those who did not.

CONCLUSION

The memory aid may be useful to a significant proportion of students.

Histopathologic study of extraocular muscles in thyroid-associated ophthalmopathy coexisting with ocular myasthenia gravis: a case report

Background

Coexistence of thyroid-associated ophthalmopathy (TAO) and ocular myasthenia gravis (OMG) is very rare. Little is known about the orbital histopathology associated with this condition. The authors reported a case of TAO coexisting with OMG and explored the histopathologic changes in extraocular muscles.

Case presentation

A 32-year-old man complaint of bilateral proptosis for 2 years. The patient was documented with a history of OMG and was treated with blepharoplasty to correct ptosis 3 years prior to presentation. Physical examination revealed right upper eyelid retraction resulting from the eyelid surgery. Computed tomographic scan demonstrated bilateral enlargement of the extraocular muscles. Thyroid function test confirmed hyperthyroid status. The patient was diagnosed with TAO (clinical activity score = 2/7) coexisting with OMG. Orbital decompression surgery reduced proptosis but resulted in new onset of left upper eyelid retraction because of the increased motor impulses to sustain eyelid elevation. Extraocular muscles were sampled during surgery and subjected to histopathologic stain. The stain results were analyzed against samples from age-, gender- matched TAO and control (non-TAO non-OMG) subjects. The measurement of myofiber size and glycosaminoglycan/collagen-occupied area was repeated in 3 randomly chosen fields of each slide. The variation of myofiber size was larger in the TAO + OMG (289.9 ± 142.5 μm²) samples than the TAO (544.1 ± 160.6 μm²) and control (157.0 ± 47.7 μm²) samples. Glycosaminoglycan was more abundant in the TAO + OMG (48.8 ± 12.2%) samples than the TAO (28.4 ± 3.6%) and control (3.3 ± 0.8%) samples. Collagen fibers accumulated in the TAO (60.5 ± 6.4%) samples but not in the TAO + OMG (36.1 ± 4.3%) and control (33.9 ± 2.7%) samples. Typical OMG changes were observed in the TAO + OMG samples but not in the TAO and control samples. These changes included central nuclei, aggregation of mitochondria and fiber type grouping. The histopathologic findings of TAO + OMG were summarized as inhomogeneously enlarged muscle fibers and predominantly endomysial accumulation of glycosaminoglycan.

Conclusion

This study highlights the possibility of TAO coexisting with OMG and demonstrates the histopathologic features in this rare condition.

Effects of Orbital Decompression on Lamina Cribrosa Depth in Patients with Graves' Orbitopathy

Purpose

We sought to investigate the effects of Graves' orbitopathy (GO) and orbital decompression on lamina cribrosa depth (LCD) using spectral-domain optical coherence tomography.

Methods

Forty eyes that underwent orbital decompression to relieve compressive optic neuropathy or correct disfiguring exophthalmos in the context of GO were included. Subjects were imaged with spectral-domain optical coherence tomography before surgery and at 1 and 3 months after surgery, at which the examiner measured the LCD (distance from the anterior surface of the lamina cribrosa to the Bruch membrane opening line) and peripapillary retinal nerve fiber layer thickness. Subjects were divided into two groups—a muscle-dominant group composed of patients who had extraocular muscle enlargement on preoperative orbital computed tomography scan and a fat-dominant group composed of patients who did not show extraocular muscle enlargement on preoperative orbital computed tomography scan—and subgroup analysis was performed. Preoperative and postoperative intraocular pressure, exophthalmos, LCD, and retinal nerve fiber layer thickness were evaluated.

Results

At baseline, LCD was remarkably shallower in the muscle-dominant group than in the fat-dominant group (95% confidence interval, p = 0.007). In the muscle-dominant group, LCD showed no definite change after surgery. However, the fat-dominant group showed temporary posterior displacement of the lamina cribrosa at 1-month postoperation that was reversed to baseline at 3 months postoperation (95% confidence interval, p < 0.01).

Conclusions

The lamina cribrosa was anteriorly displaced preoperatively, and its position was nearly unchanged after the surgery, especially in association with extraocular muscle enlargement. An enlarged extraocular muscle could reduce the pressure-relieving effect of orbital decompression around the scleral canal in patients with GO.

Using biomechanics to investigate the effect of VR on eye vergence system

Vergence-accommodation conflict (VAC) is the main contributor to visual fatigue during immersion in virtual environments. Many studies have investigated the effects of VAC using 3D displays and expensive complex apparatus and setup to create natural and conflicting viewing conditions. However, a limited number of studies targeted virtual environments simulated using modern consumer-grade VR headsets. Our main objective, in this work, is to test how the modern VR headsets (VR simulated depth) could affect our vergence system, in addition to investigating the effect of the simulated depth on the eye-gaze performance. The virtual scenario used included a common virtual object (a cube) in a simple virtual environment with no constraints placed on the head and neck movement of the subjects. We used ocular biomechanics and eye tracking to compare between vergence angles in matching (ideal) and conflicting (real) viewing conditions. Real vergence angle during immersion was significantly higher than ideal vergence angle and exhibited higher variability which leads to incorrect depth cues that affects depth perception and also leads to visual fatigue for prolonged virtual experiences. Additionally, we found that as the simulated depth increases, the ability of users to manipulate virtual objects with their eyes decreases, thus, decreasing the possibilities of interaction through eye gaze. The biomechanics model used here can be further extended to study muscular activity of eye muscles during immersion. It presents an efficient and flexible assessment tool for virtual environments.

Extraocular muscle enlargement in retinoencephalofacial angiomatosis

A 22-year-old female presented for evaluation of five years of progressive left exophthalmos and intermittent blurred vision. She had previously received laser treatment for peripheral retinal neovascularization and had undergone lip reconstruction for a left-sided congenital vascular facial malformation. Magnetic resonance imaging demonstrated diffuse enlargement of the left extraocular and temporalis muscles, with prominent vessels in the temporalis muscle and intraconal fat. Left fundoscopic examination revealed grossly enlarged, tortuous retinal vessels extending from the optic disc to the peripheral retina and an abnormal network of capillaries. On the basis of these findings, a diagnosis of retinoencephalofacial angiomatosis was established. Retinoencephalofacial angiomatosis is a rare, non-hereditary disorder associated with ipsilateral retinal, brain, and facial arteriovenous malformations. This is the first report, to the authors' knowledge, of retinoencephalofacial angiomatosis presenting with exophthalmos secondary to extraocular muscle enlargement.

Intermediate filaments in the medial rectus muscles in patients with concomitant exotropia

PURPOSE

Distribution of intermediate filament (IF) proteins in normal extraocular muscles (EOMs) showed that the EOMs differ significantly from the other muscles in the body with respect to their IFs composition, including desmin and nestin. The aim of the present study was to investigate the pathological changes in the medial rectus (MR) in patients with concomitant exotropia (XT).

METHODS

Forty-six MR muscle samples from 46 patients with XT were analyzed pathologically and processed for immunohistochemistry with specific antibodies against desmin and nestin.

RESULTS

Although most of MR muscles remained normal structures relatively, they presented high expression of desmin, and in contrast, nestin was absent in a large proportion of the MR muscles.

CONCLUSION

Desmin, which is downregulated in normal EOMs, had high expression in MR muscles of patients with XT. Nestin, which is present in a high proportion of normal EOMs, was downregulated in MR muscles of patients with XT.

Passive eye movements induced by electromagnetic force (EMF) in rats

Accurate information on eye position in the orbit is available from visual feedback, efference copy of the oculomotor commands and proprioceptive signals from the extraocular muscles (EOM). Whereas visual feedback and oculomotor commands have been extensively studied, central processing of EOM proprioceptive signals remains to be elucidated. A challenge to the field is to develop an approach to induce passive eye movements without physically contacting the eyes. A novel method was developed to generate passive eye movements in rats. A small rare-earth magnet disk (0.7 mm diameter, 0.5 mm thickness) was attached to the surface of a rat's eyeball. A metal rod (5 mm diameter) wrapped with an electromagnetic (EM) coil was placed near the magnet (8-15 mm). By passing currents to the EM coil, electromagnetic force (EMF) was generated and acted upon the magnet and induced passive eye movements. The EMF induced well-defined passive eye movements, whose directions were dependent on current polarity and amplitudes and peak velocities were dependent on current intensity and duration. Peak velocities of the EMF-induced eye movements were linearly related to amplitudes, exhibiting main sequence relationships similar to that of saccades in awake rats and eye movements induced by electrical microstimulation of the abducens nucleus in anesthetized rats. Histological examination showed that repetitive EMF stimulations did not appear to result in damages in the EOM fibers. These results validated the EMF approach as a novel tool to investigate EOM proprioceptive signals and their roles in visual localization and gaze control.

Gene expression profile of extraocular muscles following resection strabismus surgery

This paper aims to identify key biological processes triggered by resection surgery in the extraocular muscles (EOMs) of a rabbit model of strabismus surgery by studying changes in gene expression. Resection surgery was performed in the superior rectus of 16 rabbits and a group of non-operated rabbits served as control. Muscle samples were collected from groups of four animals 1, 2, 4 and 6 weeks after surgery and processed for RNA-sequencing and immunohistochemistry. We identified a total of 164; 136; 64 and 12 differentially expressed genes 1, 2, 4 and 6 weeks after surgery. Gene Ontology enrichment analysis revealed that differentially expressed genes were involved in biological pathways related to metabolism, response to stimulus mainly related with regulation of immune response, cell cycle and extracellular matrix. A complementary pathway analysis and network analysis performed with Ingenuity Pathway Analysis tool corroborated and completed these findings. Collagen I, fibronectin and versican, evaluated by immunofluorescence, showed that changes at the gene expression level resulted in variation at the protein level. Tenascin-C staining in resected muscles demonstrated the formation of new tendon and myotendinous junctions. These data provide new insights about the biological response of the EOMs to resection surgery and may form the basis for future strategies to improve the outcome of strabismus surgery.

A review of the histopathological findings in myasthenia gravis: Clues to the pathogenesis of treatment-resistance in extraocular muscles

In myasthenia gravis autoantibodies target components of the neuromuscular junction causing variable degrees of weakness. In most cases, autoantibodies trigger complement-mediated endplate damage and extraocular muscles may be most susceptible. A proportion of MG cases develop treatment-resistant ophthalmoplegia. We reviewed publications spanning 65 years reporting the histopathological findings in the muscles and extraocular muscles of myasthenic patients to determine whether pathological changes in extraocular muscles differ from non-ocular muscles. As extraocular muscles represent a unique muscle allotype we also compared their histopathology in myasthenia to those in strabismus. We found that in myasthenia gravis, the non-ocular muscles frequently demonstrate neurogenic changes regardless of myasthenic serotype. Mitochondrial stress/damage was also frequent in myasthenic muscles and possibly more evident in muscle-specific kinase antibody-positive MG. Although myasthenia-associated paralysed extraocular muscles demonstrated prominent fibro-fatty replacement and mitochondrial alterations, these features appeared commonly in paralysed extraocular muscles of any cause. We postulate that extraocular muscles may be more susceptible than limb muscles to poor contractility as a consequence of myasthenia, resulting in a cascade of atrophy signaling pathways and altered mitochondrial homeostasis which contribute to the tipping point in developing treatment-resistant myasthenic ophthalmoplegia. Early strategies to improve force generation in extraocular muscles are critical.

[Unilateral combined strabismus surgery to correct esotropia : Video article on recession of the medial rectus muscle and plication of the lateral rectus muscle]

OBJECTIVE OF SURGERY

The aim of strabismus surgery to correct esotropia is orthotropic alignment or microstrabismus to achieve best possible binocularity, a larger visual field, better appearance, and a frequently connected improved self-esteem. A widely used technique to correct esotropia is combined unilateral strabismus surgery with recession of the medial rectus muscle and plication of the lateral rectus muscle.

INDICATIONS

Indications are esotropia of various origins or decompensating esophoria over 15 prism diopters.

CONTRAINDICATIONS

Absolute contraindications are insufficient optical correction of hyperopia and sixth nerve palsy with unfinished spontaneous regeneration. A relative contraindication in children is untreated amblyopia.

SURGICAL TECHNIQUE

The technique consists of unilateral recession of the medial rectus muscle and tucking of the lateral rectus muscle. The surgical technique is demonstrated in detail in two videos of the operation, which are available online.

FOLLOW-UP

Antibiotic and lubricating eye drops are applied during the first week after surgery. In the early postoperative period, patients should be monitored for postoperative infection, conjunctival dehiscence, or corneal laceration. We review patients 4 months postoperatively for evaluation of the long-term result.

EVIDENCE

Recent randomized controlled studies have shown that unilateral medial rectus muscle recession and resection surgery is comparable to bilateral recession surgery with regards to postoperative results in esotropia. The effect of lateral rectus muscle tuck is comparable to muscle resection with less trauma and potential reversibility during the first days after surgery.

Response to tocilizumab treatment in Graves' ophthalmopathy by measuring rectus muscle thickness and chemosis using optical coherence tomography

PURPOSE

To assess the extraocular muscle thickness and chemosis after treatment with tocilizumab in patients with active Graves' ophthalmopathy by optical coherence tomography.

METHODS

Case series of five patients with active Graves' ophthalmopathy (clinical activity score ≥4/10) treated with 4 doses of tocilizumab. These patients had been previously treated with corticosteroids with no response. Spectral-domain optical coherence tomography was employed to determine lateral and medial rectus muscle thickness and chemosis before and after 4 doses of tocilizumab given monthly. Scanning was performed at 3 and 9 o'clock (nasal and temporal).

RESULTS

The study included four women and one man with a median age of 52 years (range: 38-73). Median Graves' ophthalmopathy activity duration was 17 months (12-18). Median medial rectus and determine lateral thicknesses pre-treatment were 249μm (174-366) and 337μm (142-443), respectively. Median chemosis was 409μm (290-610). After tocilizumab treatment, median muscle thicknesses reduced to 157μm (88-187) and 197μm (99-290), respectively (P=.043; Wilcoxon) and chemosis to 59μm (0-78). Median clinical activity score decreased from 5 (4-8) to 1 (0-3).

CONCLUSIONS

A reduction in extraocular muscle thickness and chemosis was observed after treatment with tocilizumab in Graves' ophthalmopathy patients using an optical coherence tomography, so this technique could be a useful complementary technique to assess the therapeutic responses.

bulbi) in the pre-hatchling and post-hatchling african black ostriches (struthio camelus domesticus L., 1758) (Aves: Struthioniformes)

The aim of the study was to describe the morphology and the development of the extraocular muscles (EOMs) in the pre-hatchling and post-hatchling African black ostrich. The study involved 50 birds aged between 28 days and 3 years. The EOMs were analyzed morphologically with respect to the location and length of the straight and oblique muscles and the third eyelid muscles, the length and breadth of their tendons as well as the distance and shape of the muscle tendon insertions at the corneal limbus. A histological and histometric analysis were also carried out. The greatest increase in the length of the EOMs was noted in groups III-V. A marked increase in the length of the tendons of the dorsal straight muscle was found in groups II and III, in the tendons of the nasal straight muscle in groups IV and V, in the tendons of the dorsal oblique muscle in groups III to V and in the tendons of the ventral oblique muscle in groups IV and V. There was a significant increase in the breadth of the dorsal straight and ventral oblique muscle tendons in groups IV and V and the tendons of the pyramidal muscle in groups III and V. The distance of the distal insertion of the tendon at the corneal limbus increased steadily with age in all the examined groups. The number of fascicles and muscle fibres, their diameter and length in all the studied EOMs were different in the different groups.

Bilateral muscular slips between superior and inferior rectus muscles: case report with discussion on classification of accessory rectus muscles within the orbit

Accessory rectus muscles have rarely been reported as muscular ‘bands’ or ‘slips’ originating from the common tendinous ring (annulus of Zinn) and inserting in atypical location. This group of muscles is innervated by the inferior branch of the oculomotor nerve, lies on lateral side of the optic nerve and inserts in rectus muscles. Since there are only few descriptions of such unusual findings in the medical literature, the anatomical data on accessory rectus muscles is limited. Furthermore, existing reports vary in terms of studied objects (cadavers or living subjects), medical history (absence or presence of ocular movement disorders or eye movement abnormalities) and details of anatomical description. This report complements earlier publications and provides complete anatomical description of the accessory rectus muscle observed bilaterally during the dissection of a 68-year-old male cadaver with no eye movement abnormalities reported in the medical history. The accessory rectus muscle was divided into two ‘slips’ or ‘heads’—superior and inferior—running in the sagittal plane (laterally to the optic nerve and the main trunk of the ophthalmic artery) and attached to the superior and inferior rectus muscles. Noticeable thickening of both superior and inferior rectus muscles at the insertion point of the accessory muscle heads was observed only in the sagittal plane. On both sides, the inferior head of the accessory rectus muscle was innervated by one of sub-branches derived from the inferior branch of the oculomotor nerve. No sub-branches to the superior head were macroscopically observed during the dissection. The classification, embryological background and clinical relevance of this variation have been discussed.

Isolation, Culture, and Immunostaining of Skeletal Muscle Myofibers from Wildtype and Nestin-GFP Mice as a Means to Analyze Satellite Cell

Multinucleated myofibers, the functional contractile units of adult skeletal muscle, harbor mononuclear Pax7+ myogenic progenitors on their surface between the myofiber basal lamina and plasmalemma. These progenitors, known as satellite cells, are the primary myogenic stem cells in adult muscle. This chapter describes our laboratory protocols for isolating, culturing, and immunostaining intact myofibers from mouse skeletal muscle as a means for studying satellite cell dynamics. The first protocol discusses myofiber isolation from the flexor digitorum brevis (FDB) muscle. These short myofibers are plated in dishes coated with PureCol collagen (formerly known as Vitrogen) and maintained in a mitogen-poor medium (± supplemental growth factors). Employing such conditions, satellite cells remain at the surface of the parent myofiber while synchronously undergoing a limited number of proliferative cycles and rapidly differentiate. The second protocol discusses the isolation of longer myofibers from the extensor digitorum longus (EDL) muscle. These EDL myofibers are routinely plated individually as adherent myofibers in wells coated with Matrigel and maintained in a mitogen-rich medium, conditions in which satellite cells migrate away from the parent myofiber, proliferate extensively, and generate numerous differentiating progeny. Alternatively, these EDL myofibers can be plated as non-adherent myofibers in uncoated wells and maintained in a mitogen-poor medium (± supplemental growth factors), conditions that retain satellite cell progeny at the myofiber niche similar to the FDB myofiber cultures. However, the adherent myofiber format is our preferred choice for monitoring satellite cells in freshly isolated (Time 0) myofibers. We conclude this chapter by promoting the Nestin-GFP transgenic mouse as an efficient tool for direct analysis of satellite cells in isolated myofibers. While satellite cells have been often detected by their expression of the Pax7 protein or the Myf5nLacZ knockin reporter (approaches that are also detailed herein), the Nestin-GFP reporter distinctively permits quantification of satellite cells in live myofibers, which enables linking initial Time 0 numbers and subsequent performance upon culturing. We additionally point out to the implementation of the Nestin-GFP transgene for monitoring other selective cell lineages as illustrated by GFP expression in capillaries, endothelial tubes and neuronal cells. Myofibers from other types of muscles, such as diaphragm, masseter, and extraocular, can also be isolated and analyzed using protocols described herein. Collectively, this chapter provides essential tools for studying satellite cells in their native position and their interplay with the parent myofiber.

The biomechanical significance of pulley on binocular vision

Background

Pulleys have been reported as the functional origins of the rectus extraocular muscles (EOMs). However, biomechanical significance of pulleys on binocular vision has not been reported.

Methods

Three eye movement models, i.e., non-pulley model, passive-pulley model, and active-pulley model, are used to simulate the horizontal movement of the eyes from the primary position to the left direction in the range of 1°–30°. The resultant forces of six EOMs along both orthogonal directions (i.e., the x-axis and y-axis defined in this paper) in the horizontal plane are calculated using the three models.

Results

The resultant force along the y-axis of the left eye for non-pulley model are significantly larger than that of the other two pulley models. The difference of the force, between the left eye and the right eye in non-pulley model, is larger than those in the other two pulley models along x-axis and y-axis.

Conclusion

The pulley models present more biomechanical advantage on the horizontally binocular vision than the non-pulley model. Combining with the previous imaging evidences of pulleys, the results show that pulley model coincides well with the real physiological conditions.

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.

Distance between intramuscular nerve and artery in the extraocular muscles: a preliminary immunohistochemical study using elderly human cadavers

PURPOSE

Extraocular muscles are quite different from skeletal muscles in muscle fiber type and nerve supply; the small motor unit may be the most well known. As the first step to understanding the nerve-artery relationship, in this study we measured the distance from the arteriole (25-50 μm in thickness) to the nerve terminal twigs in extraocular muscles.

MATERIALS AND METHODS

With the aid of immunohistochemistry for nerves and arteries, we examined the arteriole-nerve distance at 10-15 sites in each of 68 extraocular muscles obtained from ten elderly cadavers. The oblique sections were nearly tangential to the muscle plate and included both global and orbital aspects of the muscle.

RESULTS

In all muscles, the nerve twigs usually took a course parallel to muscle fibers, in contrast to most arterioles that crossed muscles. Possibly due to polyinnervation, an intramuscular nerve plexus was evident in four rectus and two oblique muscles. The arteriole-nerve distance usually ranged from 300 to 400 μm. However, individual differences were more than two times greater in each of seven muscles. Moreover, in each muscle the difference between sites sometimes reached 1 mm or more. The distance was generally shorter in the rectus and oblique muscles than in the levator palpebrae muscle, which reached statistical significance (p < 0.05).

CONCLUSIONS

The differences in arteriole-nerve distances between sites within each muscle, between muscles, and between individuals might lead to an individual biological rhythm of fatigue in oculomotor performance.

Presumed isotretinoin-induced extraocular myopathy

Isotretinoin a synthetic analogue of vitamin A is primarily used for cystic acne not responding to conventional treatment. Several ocular side effects including blurring of vision, decreased dark adaptation, corneal opacities and meibomian gland atrophy have been reported with prolonged use of isotretinoin. There have been reports of muscular damage caused by isotretinoin. Extra ocular myopathy as an adverse effect of long term used of isotretinoin has never been mentioned in literature. We report a case of a young male who presented to us with complaints of diplopia after using isotretinoin for a prolonged period. He was diagnosed as a case of presumed isotretinoin extraocular myopathy after imaging and other blood investigations.