Diffusion tensor imaging of horizontal extraocular muscles in patients with concomitant and paralytic esotropia

AIM:To assess metrics of diffusion tensor imagining(DTI)in evaluating microstructural abnormalities of horizontal extraocular muscles(EOM)in esotropia.METHODS:Six adult concomitant esotropia patients,5 unilateral abducent paralysis patients and 2 healthy volunteers were enrolled.Conventional magnetic resonance imaging(MRI)and DTI were performed on all subjects using 3T MR scanner.Fractional anisotropy(FA),mean diffusivity(MD),axial diffusivity(AD),and radial diffusivity(RD)of medial and lateral rectus muscles were measured and compared between patients group and control group.RESULTS:Medial rectus MD and RD within the adducted eye of concomitant patients was significantly greater than that in unilateral abducent paralysis patients(0.259×10-2 mm^(2)/s vs 0.207×10-2 mm^(2)/s,P=0.014;0.182×10-2 mm^(2)/s vs 0.152×10-2 mm^(2)/s,P=0.017).Both strabismus patients showed a significantly decreased MD and AD than that obtained in normal controls for lateral rectus muscles(P<0.05).Medial rectus MD of the adducted eye in concomitant strabismus patients was significantly decreased than that in healthy controls(0.259×10-2 mm^(2)/s vs 0.266×10-2 mm^(2)/s,P=0.010).Lateral rectus AD of the adducted eye in concomitant strabismus patients was significantly decreased as compared with that in healthy controls(0.515×10-2 mm^(2)/s vs 0.593×10-2 mm^(2)/s,P=0.013).No statistically significant differences were present between the adducted and fixating eyes in concomitant strabismus patients.CONCLUSION:DTI represents a feasible technique to assess tissue characteristics of EOM.The effects of eye position changes on DTI parameters are subtle.Decreased MD and RD could be evidence for remodeling of the medial rectus muscle contracture.Lower medial and lateral recuts MD of concomitant esotropia patients indicates a thinner fibrous structure of the EOM.Lower MD and AD should be general character of esotropia.

Magnetic resonance imaging of extraocular rectus muscles abnormalities in acute acquired concomitant esotropia

AIM:To investigate the difference of medial rectus(MR)and lateral rectus(LR)between acute acquired concomitant esotropia(AACE)and the healthy controls(HCs)detected by magnetic resonance imaging(MRI).METHODS:A case-control study.Eighteen subjects with AACE and eighteen HCs were enrolled.MRI scanning data were conducted in target-controlled central gaze with a 3-Tesla magnetic resonance scanner.Extraocular muscles(EOMs)were scanned in contiguous image planes 2-mm thick spanning the EOM origins to the globe equator.To form posterior partial volumes(PPVs),the LR and MR cross-sections in the image planes 8,10,12,and 14 mm posterior to the globe were summed and multiplied by the 2-mm slice thickness.The data were classified according to the right eye,left eye,dominant eye,and non-dominant eye,and the differences in mean cross-sectional area,maximum cross-sectional area,and PPVs of the MR and LR muscle in the AACE group and HCs group were compared under the above classifications respectively.RESULTS:There were no significant differences between the two groups of demographic characteristics.The mean cross-sectional area of the LR muscle was significantly greater in the AACE group than that in the HCs group in the non-dominant eyes(P=0.028).The maximum cross-sectional area of the LR muscle both in the dominant and non-dominant eye of the AACE group was significantly greater than the HCs group(P=0.009,P=0.016).For the dominant eye,the PPVs of the LR muscle were significantly greater in the AACE than that in the HCs group(P=0.013),but not in the MR muscle(P=0.698).CONCLUSION:The size and volume of muscles dominant eyes of AACE subjects change significantly to overcome binocular diplopia.The LR muscle become larger to compensate for the enhanced convergence in the AACE.

Magnetic resonance imaging of the extraocular muscles and corresponding cranial nerves in patients with special forms of strabismus

Background With the technical advances, magnetic resonance imaging （MRI） is now sensitive enough to detect subtle structural abnormalities of ocular motor nerves arising from the brainstem and orbits of living subjects. This study was designed to delineate the MRI characteristics in patients with special forms of strabismus. Methods A total of 29 patients with special forms of strabismus underwent orbital and intracalvafium MRI. Imaging of the ocular motor nerves in the brainstem was performed in 0.8 mm thickness image planes using the three-dimensional fast imaging employing steady-state acquisition （3D-FIESTA） sequence. Nerves to extraocular muscles （EOMs）, EOMs and their associated connective tissues were imaged with T1 weighting in tri-planar scans by dual-phased coils within 2.0 mm thick planes. Results Patients with congenital fibrosis of the extraocular muscles exhibited hypoplasia of the oculomotor （CN3）, abducens （CN6）, trochlear （CN4） nerves, and the EOMs; hypoplasia of CN6 in the brainstem and an extra branch of the inferior division of CN3 to the lateral rectus were the most common but not the only presentation of Duane＇s retraction syndrome. Hypoplasia of CN6, facial （CN7） and hypoglossal （CN12） nerves were revealed in patients with MSbius syndrome. In a rare case of bilateral synergistic convergence and divergence, an enlarged branch of CN3 to the medial rectus and a questionable branch of CN3 to the inferior rectus bilaterally were found. Conclusion MRI can reveal subtle structures of the ocular motor nerves and their corresponding EOMs. This can provide valuable information regarding pathogenesis in some special forms of strabismus.

Normative Measurements of Extraocular Musculature by Multislice Computed Tomography

Objective To establish the normal measurements of diameter of extraocular muscles (EOMs) by multislice computed tomography (CT). Methods Orbits of 50 volunteers (25 male and 25 female) were scanned with a multislice CT scanner. For each subject, one axial image at the central level of the eyeball, one coronal image about 1 cm behind globe, and two oblique sagittal images respectively along the left and right optic nerve were used for measurements of the thickness and width of EOMs. The statistic significance of measurement value between male and female and between left and right eyes was evaluated. Results There were no significant differences in the thickness and width of superior muscle group, lateral rectus, medial rectus, lateral rectus, superior oblique, inferior oblique and the thickness of levator palpebrae superioris between the left and right eyes as well as between male and female groups (all P>0.05). The thickness of superior muscle group and inferior rectus had not significant difference (2.9±0.7 vs. 3.3±0.8 mm, P=0.162), while the thickness of medial rectus was significantly higher than that of lateral rectus (3.1±0.5 vs. 2.2±0.6 mm, P=0.000). Conclusions The CT measurement of extraocular musculature is simple and time-saving and can be applied in the clinical work. The normative data obtained may be useful in determining pathologic enlargement of the EOMs in both thyroid-associated orbitopathy patients and other various orbital conditions.

Establishment of an acute extraocular muscle injury model in cats

AIM： To describe an acute extraocular muscle injury model in cats. METHODS： Seventy-two cats were randomly divided into 6 groups（12 cats per group）. Cats＇ left lateral recti were clamped using a surgical needle holder with a clamping strength of 2（Groups A and D）, 4（Groups B and E） and 6 kg（Groups C and F）. The right lateral recti were treated as controls. On the 4^（th） and 7^（th） days, hematoxylin eosin（HE） staining, immunohistochemical staining for proliferating cell nuclear antigen（PCNA）, muscle force measurements and ocular alignment changes were performed to evaluate the extent of injuries. RESULTS： The morphological changes were graded as mild, moderate or severe by HE staining in all experiment groups. PCNA immunohistochemical staining indicated repairment of muscle fibers in the damaged area. On the 4^（th） and 7^（th） days after clamping, the injured lateral muscle exhibited an elevated threshold for electric stimulation. The muscle forces among groups 2, 4 and 6 kg injury at 4 d（Groups A, B and C） were statistically significant（P0.05）, respectively. In addition, medial deviation in ocular alignment was also present to various degrees in all groups. CONCLUSION： A cat model of acute extraocular muscle injury can be established by rectus clamping. Different clamping strengths can make different degrees of muscle injury. This model may help the future study in the acute extraocular muscle injury.

Evaluation of nintedanib as a new postoperative antiscarring agent in experimental extraocular muscle surgery

AIM:To investigate the efficacy of nintedanib on reducing postoperative inflammation,fibrosis and adhesion formation following extraocular muscle surgery in rabbits in comparison with triamcinolone acetonide(TA).METHODS:Reinsertion of superior rectus muscle in right eyes of 30 New Zealand white rabbits were performed.They were randomized to receive one of the following treatments:0.9%normal saline,one of 1-,5-,and 10μmol doses of nintedanib subconjunctivally immediately after surgery and on postoperative day 1,2,3,5,and 7,and TA immediately after surgery.As a control group,unoperated left eyes(n=6)were used.On the 28 th day,six eyes from each group were enucleated and histopathologically and immunohistochemically analyzed to assess the postoperative inflammatory changes,fibrosis and adhesion.Transforming growth factor beta,matrix metalloproteinase-2 and alpha smooth muscle actin expressions were evaluated.RESULTS:Conjunctival and scleral inflammation in TA and nintedanib groups were significantly reduced compared to saline(sham)group.Conjunctival vascularity and rectus muscle fibrosis were significantly reduced in 10μmol nintedanib group.Nintedanib groups were the most effective groups in reduction of perimuscular fibrosis.Neither three nintedanib groups nor TA group differed statistically from sham group with regard to adhesion.The expressions of transforming growth factor beta,alpha smooth muscle actin and matrix metalloproteinase-2 were reduced in nintedanib groups compared to saline group.CONCLUSION:Nintedanib appears to attenuate postoperative inflammation and fibrosis after extraocular muscle surgery.Nintedanib may be a safer and stronger alternative agent in extraocular muscle surgery when compared to steroids.Further investigation is needed to prove antiadhesive effect of nintedanib.

A novel three-dimensional electric ophthalmotrope for improving the teaching of ocular movements

AIM: To develop a novel three-dimensional(3D) electric ophthalmotrope to improve the ophthalmology teaching effectiveness and evaluate the teaching value. METHODS: A 3D electric ophthalmotrope was designed by simulating the movement of the ocular and the extraocular muscles according to Sherrington’s law. The model with joint bearing was to ensure the flexibility and centripetal rotation of the simulated ball and stepper motor as the driving device. A programmable processor was used to control the motion amplitude of the stepper motor. The size of hole was set at the back of the simulated shell to limit the amount of eye movement. Afterwards, using a 5-point Likert scale, 7 experts evaluated the 3D electric ophthalmotrope’s simulation ability and precision, compared with the traditional anatomical model. In addition, the teaching effectiveness of the 3D electric ophthalmotrope was evaluated at in-class quiz and final exam in a randomized controlled trial. RESULTS: The 3D electric ophthalmotrope could be operated easily to demonstrate the eye movements with motion of different ocular muscles. The experts agreed that the 3D electric ophthalmotrope was different from the traditional model and was easier for students to understand every extraocular muscles’ movement in each evaluation index(P<0.05). Moreover, the results of teaching effectiveness showed that the 3D electric ophthalmotrope were significantly greater than the traditional model both at in-class quiz(P<0.01) and final exam(P<0.05). CONCLUSION: This novel 3D electric ophthalmotrope is better than the traditional model, which can be to improve the ophthalmology teaching effectiveness for students to understand the extraocular muscles’ movement.

Congenital dysplasia involving both medial and inferior recti: clinical features and surgical outcomes

AIM: To investigate the clinical features and surgical outcomes of congenital dysplasia involving both inferior recti(IR) and medial recti(MR) muscles.METHODS: A retrospective review was conducted including cases of simultaneous congenital dysplasia of IR and MR that were diagnosed and surgically treated at the Zhongshan Ophthalmic Center, Sun Yat-sen University, China, from July 2009 to November 2019. Ocular motility, ocular alignment at distance(6 m) and near(33 cm) by prism alternating cover test and stereoacuity were assessed in all patients before and after surgery. RESULTS: A total of five patients(four males and one female;three with right eye and two with left eye congenital dysplasia) were included in this review. The patients ranged in age from 10 to 42 y(21±13.4 y). The main clinical findings were hypertropia and exotropia of the affected eye, along with motility limitations in adduction and depression. Lateral rectus(LR) recession/transposition combined with IR resection was performed in one case. Two scheduled surgeries were performed in four cases, with one involving superior rectus recession and IR resection and the others LR recession and MR resection. Mean±SD pre-surgical exotropia of 51.0±31.11 prism diopter(PD) and hypertropia of 29.20±7.12 PD in the primary position were decreased to 3.6±12.90 and 3.2±10.09 PD, respectively, at two years after surgery, with a success rate of 60% and an undercorrection rate of 40%. CONCLUSION: The main clinical features associated with simultaneous MR/IR congenital dysplasia are hypertropia and exotropia of the affected eye along with motility limitations in adduction and depression. Scheduled two-stage surgeries achieved a success rate of 60%.

Magnetic Resonance Imaging Features of Extraocular Muscle Lymphoma in Five Cases

Lymphoma is the most common primary orbital malignant neoplasm in adults,accounting for 8-15% of extranodal non-Hodgkin＇s lymphomas and 2% of all lymphomas.Most of these tumors involve the conjunctiva,orbit,lacrimal gland,or eyelid.It is uncommon for lymphoma to originate from the extraocular muscles.The prevalence of intramuscular lymphoma is between 0.1% and 8.7% of all extranodal lymphomas.Fewer than 60 cases have been reported in the last 30 years, mostly as case reports with scant or no radiology information.

Using the traditional model to evaluate the active force of the human lateral rectus muscle

The information on the force of extraocular muscles(EOMs)is beneficial for strabismus diagnosis and surgical planning,and a direct and simple method is important for surgeons to obtain these forces.Based on the traditional model,a numerical simulation method was proposed to achieve this aim,and then the active force of the lateral rectus(LR)muscle was successfully simulated when the eye rotated every angle from 0°to 30°in the horizontal plane from the nasal to the temporal side.In order to verify these simulations,the results were compared with the previous experimental data.The comparison shows that the simulation results diverged much more than the experimental data in the range of 0°–10°.The errors were corrected to make the simulation results closer to the experimental data.Finally,a general empirical equation was proposed to evaluate the active force of the LR muscle by fitting these data,which represent the relationship between the simulation forces and the contractive amounts of the LR muscle.