Rectus Extraocular Muscle Paths and Staphylomata in High Myopia

Finite element model of ocular adduction with unconstrained globe translation

Details of the anatomy and behavior of the structures responsible for human eye movements have been extensively elaborated since the first modern biomechanical models were introduced. Based on these findings, a finite element model of human ocular adduction is developed based on connective anatomy and measured optic nerve (ON) properties, as well as active contractility of bilaminar extraocular muscles (EOMs), but incorporating the novel feature that globe translation is not otherwise constrained so that realistic kinematics can be simulated. Anatomy of the hemisymmetric model is defined by magnetic resonance imaging. The globe is modeled as suspended by anatomically realistic connective tissues, orbital fat, and contiguous ON. The model incorporates a material subroutine that implements active EOM contraction based on fiber twitch characteristics. Starting from the initial condition of 26° adduction, the medial rectus (MR) muscle was commanded to contract as the lateral rectus (LR) relaxed. We alternatively modeled absence or presence of orbital fat. During pursuit-like adduction from 26 to 32°, the globe translated 0.52 mm posteriorly and 0.1 mm medially with orbital fat present, but 1.2 mm posteriorly and 0.1 mm medially without fat. Maximum principal strains in the optic disk and peripapillary reached 0.05-0.06, and von-Mises stress 96 kPa. Tension in the MR orbital layer was ~ 24 g-force after 6° adduction, but only ~ 3 gm-f in the whole LR. This physiologically plausible simulation of EOM activation in an anatomically realistic globe suspensory system demonstrates that orbital connective tissues and fat are integral to the biomechanics of adduction, including loading by the ON.

Modified partial Jensen procedure to treat a hypertropic Knobby eye syndrome in a high myopic monocular patient

We present a case of severe esotropia and hypertropia in a monocular high myope with an inferolateral staphyloma. Surgery was undertaken to secure the inferior rectus to the lateral rectus via a modified partial Jensen technique, along with medial rectus recession successfully improving head and eye positions and ductions.

Magnetic resonance imaging findings of high myopic strabismus with sagging eye-like symptoms, heavy eye syndrome, and non-highly myopic eyes with sagging eye syndrome

INTRODUCTION

Progressive esotropia accompanied by restricted abduction and supraduction due to high myopia is known as esotropia fixus with high myopia or heavy eye syndrome (HES). Some conditions, such as sagging eye syndrome (SES), show esotropia for distance or cyclovertical strabismus with no abduction limitations despite highly myopic eyes. We evaluated the magnetic resonance imaging (MRI) findings and clinical features of HES, high myopia with SES-like symptoms (highly myopic SES), and SES.

METHODS

We reviewed all patients diagnosed with HES, highly myopic SES, and SES who underwent MRI of the orbits and brain over 6 years. To quantitatively assess the orbital anatomy, we compared the conditions of the superior rectus muscle (SR), lateral rectus muscle (LR), and inferior rectus muscle (IR) using orbital MRI among the three groups.

RESULTS

Among the 14 patients (27 eyes) with high myopia, 5 (9 eyes) had HES, and 9 (18 eyes) had highly myopic SES. Eleven patients (22 eyes) with SES were also compared with these 14 patients. The mean axial length was 29.6 ± 1.0 mm in participants with HES, 29.0 ± 1.5 mm in those with HES-SES, and 23.7 ± 0.9 mm in those with SES. The average distance esotropia was 48.0 ± 19.9Δprism, 4.6 ± 1.5Δprism, and 6.1 ± 4.6Δprism for participants with HES, highly myopic SES and SES, respectively. The average distance hypertropia was 5.3 ± 5.9Δprism in participants with highly myopic SES and 4.8 ± 2.7Δprism in those with SES. The mean vertical angle of the LR was 32.6 ± 10.8°, 18.1 ± 5.4°, and 14.6 ± 6.8°; the mean tilting angle of the LR was 31.6 ± 9.2°, 15.9 ± 6.0°, and 13.8 ± 5.9°; and the mean displacement angle between the LR and SR was 152.3 ± 16.7°, 125.0 ± 7.1°, and 112.5 ± 7.5° for participants with HES, highly myopic SES and SES, respectively. The LR-SR displacement angle in HES-SES was significantly larger than in SES (p < .001) but the vertical and tilting angles were not. Also, the IR shift showed no significant difference with HES-SES and HES (5.8 ± 1.4 mm and 5.3 ± 1.2 mm) but not with SES (4.0 ± 0.8 mm) (p < .0001).

DISCUSSION

SES-like symptoms can develop in highly myopic eyes; however, MRI showed that the state of the LR muscle in highly myopic SES deviated almost similarly to that in SES; however, the eyeball was more dislocated than in SES. This may be useful in deciding the appropriate operative procedure.

Inferior displacement of the lateral rectus muscle insertion in exotropia with mild V-pattern or vertical deviation

BACKGROUND

To describe clinical features and intraoperative findings of the patients with exotropia who presented mild V-pattern or vertical deviation, and to investigate the surgical outcomes of anatomical relocation of inferiorly displaced lateral rectus (LR) muscle insertion.

METHODS

Detailed ophthalmological evaluations were obtained in 42 consecutive patients, and the horizontal rectus muscle insertions were detected intraoperatively. The displaced insertion of LR muscle was corrected accompanied with classic recession-resection procedure.

RESULTS

The inferiorly displaced LR muscle insertions were detected in 19 patients (Group A), while the remaining 23 patients (Group B) had normal insertions. The mean distance of displaced insertion from the normal position was 2.92 ± 1.05 mm (range: 1.0-4.0). Mild V-pattern was more common in Group A (78.9%, 15/19) than Group B (47.8%, 11/23), and the magnitude of V-pattern in Group A (6.16 ± 3.91 PD) was also greater than Group B (3.43 ± 3.92 PD). The fundus extorsions of the affected eyes (9.68 ± 4.77 °) were greater than the contralateral eyes (5.91 ± 5.82 °) in Group A. At the 2 months follow-up, mild V-pattern and mild vertical deviation were corrected by upward transposition. The significant correlations were identified between the pre-operative misalignments and the amounts of misalignments correction.

CONCLUSIONS

Nearly half of the cases with mild V-pattern or vertical deviation resulted from the inferiorly displaced LR muscle insertion, so the intraoperative exploration of the LR muscle insertion is strongly suggested. Upward transposition may effectively correct both the mild V-pattern and vertical deviation.

Assessment of Ocular Deformation in Pathologic Myopia Using 3-Dimensional Magnetic Resonance Imaging

IMPORTANCE

Ocular deformation in pathologic myopia can affect the entire globe. However, few studies have investigated the equatorial pattern of ocular shape. In addition, the correlation between equatorial and posterior morphology needs to be further explored.

OBJECTIVE

To assess global ocular deformation in pathologic myopia.

DESIGN, SETTING, AND PARTICIPANTS

This hospital-based, cross-sectional study included 180 pathologic myopic eyes with atrophic maculopathy grading C2 (diffuse chorioretinal atrophy) or more from 180 participants who underwent comprehensive ophthalmic examination, including high-resolution 3-dimensional magnetic resonance imaging. In addition, 10 nonpathologic myopic eyes of 10 participants were set as the control group.

Main Outcomes and Measures

According to the cross-sectional view of equator, equatorial shape was classified as round, rectangular, pyriform (noncircular and more protruded in 1 direction), vertical-elliptical, or horizontal-elliptical; according to the nasal and inferior views, the posterior shape was categorized as spheroidal, conical, bulb-shaped, ellipsoidal, multidistorted, and barrel-shaped. Equatorial circularity and ocular sphericity were used to quantitatively assess the morphological variability of the equatorial and posterior regions, respectively. The association between ocular morphology and ocular parameters and myopic maculopathy was also investigated.

Results

The mean (SD) age of 180 participants with pathologic myopia was 55.14 (10.74) years, 127 were female (70.6%), and the mean (SD) axial length of studied eyes was 30.22 (2.25) mm. The predominant equatorial shape was pyriform (66 eyes [36.7%]), followed by round (45 eyes [25.0%]). The predominant posterior shape was bulb-shaped (97 eyes [52.2%]), followed by multidistorted (46 eyes [24.7%]). Equatorial circularity and equatorial shapes were correlated (r = -0.469; 95% CI, -0.584 to -0.346; P < .001) and ocular sphericity was correlated with posterior shapes (r = -0.533; 95% CI, -0.627 to -0.427; P < .001). In eyes with a vertical-elliptical equator, equatorial circularity and ocular sphericity were positively linearly correlated (R2 = 0.246; 95% CI, 0.050-0.496; P = .002) and the prevalence of inferior staphyloma was higher (27.8%; P = .04). Eyes with a horizontal-elliptical equator have the most horizontally oriented axis of corneal flat keratometry (median, 43.55 [interquartile range, 43.84] degrees; P = .01) and tended to present with multidistorted posterior shape (21.7%; P = .04).

Conclusions and Relevance

These findings suggest ocular deformation is common in pathologic myopia and can affect the entire eye, including the equatorial and posterior regions. The morphological classification may enhance the understanding of the diverse patterns of ocular shape in pathologic myopia.

Linear viscoelasticity of human sclera and posterior ocular tissues during tensile creep

PURPOSE

Despite presumed relevance to ocular diseases, the viscoelastic properties of the posterior human eye have not been evaluated in detail. We performed creep testing to characterize the viscoelastic properties of ocular regions, including the sclera, optic nerve (ON) and ON sheath.

METHODS

We tested 10 pairs of postmortem human eyes of average age 77 ± 17 years, consisting of 5 males and 5 females. Except for the ON that was tested in native shape, tissues were trimmed into rectangles. With physiologic temperature and constant wetting, tissues were rapidly loaded to tensile stress that was maintained by servo feedback as length was monitored for 1,500 sec. Relaxation modulus was computed using Prony series, and Deborah numbers estimated for times scales of physiological eye movements.

RESULTS

Correlation between creep rate and applied stress level was negligible for all tissues, permitting description as linear viscoelastic materials characterized by lumped parameter compliance equations for limiting behaviors. The ON was the most compliant, and anterior sclera least compliant, with similar intermediate values for posterior sclera and ON sheath. Sensitivity analysis demonstrated that linear behavior eventually become dominant after long time. For the range of typical pursuit tracking, all tissues exhibit Debora numbers less than 75, and should be regarded as viscoelastic. With a 6.7 Deborah number, this is especially so for the ON during pursuit and convergence.

CONCLUSIONS

Posterior ocular tissues exhibit creep consistent with linear viscoelasticity necessary for describing biomechanical behavior of the ON, its sheath, and sclera during physiological eye movements and eccentric ocular fixations. Running Head: Tensile Creep of Human Ocular Tissues.

Globe luxation may prevent myopia in a child: A case report

BACKGROUND

Globe luxation is rare and is mostly due to direct orbital trauma with fractures of the medial and floor walls, which displace the globe into the maxillary sinus. Only a few cases have been reported; moreover, patients who suffer global luxation rarely achieve eyesight recovery.

CASE SUMMARY

This report describes the treatment and prognosis of global luxation occurring in a child. A 6-year-old boy presented with left globe luxation that occurred after a sudden stop on a tricycle, without any injury to the orbital or maxillofacial bony structures. After admission to the hospital, an external canthus incision, globe repositioning, orbital exploration and temporary blepharoplasty were performed. Finally, the child completely recovered and maintained good eyesight in his left eye even though the right eye developed myopia after four years of follow-up.

CONCLUSION

The aim of this study was to report the special occurrence of globe luxation in the child and share some experience of the treatment. Immediate surgical management plays an important role in the recovery of visual function, and globe luxation may prevent nearsightedness by reducing the distortion of the eyeball, shortening the axis and improving ciliary function.

Mutational screening of AGRN, SLC39A5, SCO2, P4HA2, BSG, ZNF644, and CPSF1 in a Chinese cohort of 103 patients with nonsyndromic high myopia

Purpose

High myopia (HM) is one of the leading causes of irreversible vision loss in the world. Many myopia loci have been uncovered with linkage analysis, genome-wide association studies, and sequencing analysis. Numerous pathogenic genes within these loci have been detected in a portion of HM cases. In the present study, we aimed to investigate the genetic basis of 103 patients with nonsyndromic HM, focusing on the reported causal genes.

Methods

A total of 103 affected individuals with nonsyndromic HM were recruited, including 101 patients with unrelated sporadic HM and a mother and son pair. All participants underwent comprehensive ophthalmic examinations, and genomic DNA samples were extracted from the peripheral blood. Whole exome sequencing was performed on the mother and son pair as well as on the unaffected father. Sanger sequencing was used to identify mutations in the remaining 101 patients. Bioinformatics analysis was subsequently applied to verify the mutations.

Results

An extremely rare mutation in AGRN (c.2627A>T, p.K876M) was identified in the mother and son pair but not in the unaffected father. Another two mutations in AGRN (c.4787C>T, p.P1596L/c.5056G>A, p.G1686S) were identified in two unrelated patients. A total of eight heterozygous variants potentially affecting the protein function were detected in eight of the remaining 99 patients, including c.1350delC, p.V451Cfs*76 and c.1023_1024insA, p.P342Tfs*41 in SLC39A5; c.244_246delAAG, p.K82del in SCO2; c.545A>G, p.Y182C in P4HA2; c.415C>T, p.P139S in BSG; c.3266A>G, p.Y1089C in ZNF644; and c.2252C>T, p.S751L and c.1708C>T, p.R570C in CPSF1. Multiple bioinformatics analyses were conducted, and a comparison to a group with geographically matched controls was performed, which supported the potential pathogenicity of these variants.

Conclusions

We provide further evidence for the potential role of AGRN in HM inheritance and enlarged the current genetic spectrum of nonsyndromic HM by comprehensively screening the reported causal genes.

The Associations of Obstructive Sleep Apnea and Eye Disorders: Potential Insights into Pathogenesis and Treatment

Purpose of Review

Obstructive sleep apnea (OSA) patients are at significantly increased risks for cardiovascular and cerebrovascular morbidities. Recently, there has been heightened interest in the association of OSA with numerous ocular diseases and possible improvement of these conditions with the initiation of OSA treatment. We reviewed the current evidence with an emphasis on the overlapping pathogeneses of both diseases.

Recent Findings

Currently available literature points to a substantial association of OSA with ocular diseases, ranging from those involving the eyelid to optic neuropathies and retinal vascular diseases. Since the retina is one of the highest oxygen-consuming tissues in the body, the intermittent hypoxia and hypercapnia ensuing in OSA can have deleterious effects on ocular function and health. Tissue hypoxia, autonomic dysfunction, microvascular dysfunction, and inflammation all play important roles in the pathogenesis of both OSA and ocular diseases. Whether OSA treatment is capable of reversing the course of associated ocular diseases remains to be determined. It is anticipated that future therapeutic approaches will target the common underlying pathophysiologic mechanisms and promote favorable effects on the treatment of known associated ocular diseases.

Summary

Emerging evidence supports the association of ocular diseases with untreated OSA. Future studies focusing on whether therapeutic approaches targeting the common pathophysiologic mechanisms will be beneficial for the course of both diseases are warranted.

Material properties and effect of preconditioning of human sclera, optic nerve, and optic nerve sheath

The optic nerve (ON) is a recently recognized tractional load on the eye during larger horizontal eye rotations. In order to understand the mechanical behavior of the eye during adduction, it is necessary to characterize material properties of the sclera, ON, and in particular its sheath. We performed tensile loading of specimens taken from fresh postmortem human eyes to characterize the range of variation in their biomechanical properties and determine the effect of preconditioning. We fitted reduced polynomial hyperelastic models to represent the nonlinear tensile behavior of the anterior, equatorial, posterior, and peripapillary sclera, as well as the ON and its sheath. For comparison, we analyzed tangent moduli in low and high strain regions to represent stiffness. Scleral stiffness generally decreased from anterior to posterior ocular regions. The ON had the lowest tangent modulus, but was surrounded by a much stiffer sheath. The low-strain hyperelastic behaviors of adjacent anatomical regions of the ON, ON sheath, and posterior sclera were similar as appropriate to avoid discontinuities at their boundaries. Regional stiffnesses within individual eyes were moderately correlated, implying that mechanical properties in one region of an eye do not reliably reflect properties of another region of that eye, and that potentially pathological combinations could occur in an eye if regional properties are discrepant. Preconditioning modestly stiffened ocular tissues, except peripapillary sclera that softened. The nonlinear mechanical behavior of posterior ocular tissues permits their stresses to match closely at low strains, although progressively increasing strain causes particularly great stress in the peripapillary region.

Characterization of the position of the extraocular muscles and orbit in acquired esotropia both at distance and near using orbital magnetic resonance imaging

PURPOSE

Age-related distance esotropia (ARDE) involves acquired esotropia at distance and phoria at near. However, distance-independent esotropia (DIE) exists esotropia both at distance and near. Thus, we examined the orbital magnetic resonance imaging (MRI) findings for DIE to assess differences in its characteristics.

METHODS

This study was a retrospective case-control study. We evaluated the efficacy of the standard coronal MRI in patients with acquired esotropia and control patients with optic neuritis. Cases with strabismus in the control group were excluded. DIE was defined as having esotropia both at distance and near, and an angle of more than 10 prism diopters at near. The condition of the lateral rectus-superior rectus band, position of rectus muscles, and the volume ratio of the globe to the whole orbit (G/WO) were examined.

RESULTS

The DIE group consisted of 12 eyes of 6 patients (77.3±7.7 years); ARDE group, 38 eyes of 19 patients (73.1±6.8 years); and control group, 34 eyes of 17 patients (70.9±4.3 years). The ratio of abnormality of the lateral rectus-superior rectus bands was higher in the DIE and ARDE groups than in the control group (p<0.01). The vertical angle of the lateral rectus deviated downwards in the control (-7.5±5.1°), ARDE (-12.2±9.1°), and DIE groups (-18.8±5.7°) (p<0.05). The tilting angle of the lateral rectus was tilted temporally in the control (-12.2±9.1°), ARDE (-20.0±8.6°) and DIE groups (-28.6±5.4°) (p<0.01). G/WO was higher in the DIE (0.28±0.01) and ARDE groups (0.27±0.02) compared to the control (0.25±0.03) group (p<0.01).

CONCLUSION

In comparison with the ARDE and control groups, the DIE group presented with abnormalities of the lateral rectus-superior rectus band, malposition of the lateral rectus, and differences in the G/WO. The DIE group showed a more severe form of ARDE.

Finite Element Model of Ocular Adduction by Active Extraocular Muscle Contraction

Purpose

In order to clarify the role of the optic nerve (ON) as a load on ocular rotation, we developed a finite element model (FEM) of incremental adduction induced by active contractility of extraocular muscles (EOMs), with and without tethering by the ON.

Methods

Three-dimensional (3-D) horizontal rectus EOM geometries were obtained from magnetic resonance imaging of five healthy adults, and measured constitutive tissue properties were used. Active and passive strain energies of EOMs were defined using ABAQUS (Dassault Systemes) software. All deformations were assumed to be caused by EOM twitch activation that rotated the eye about a fixed center. The medial rectus (MR) muscle was commanded to additionally contract starting from 26 degrees adducted position, and the lateral rectus (LR) to relax, further adducting the eye either with or without loading by the ON. Tridimensional heat maps were generated to represent the stress and strain distributions.

Results

Tensions in the EOMs were physiologically plausible during incremental adduction. Force in the MR increased from 10 gm at 26 degrees adduction to approximately 28 gm at 32 degrees adduction. Under identical MR contraction, adduction with ON loading reached 32 degrees but 36 degrees without it. Maximum and minimum principal strains within the MR were 16% and 22%, respectively, but when ON loading was included, resulting stress and strain were concentrated at the optic disc.

Conclusions

This physiologically plausible method of simulating EOM activation can provide realistic input to model biomechanical behavior of active and passive tissues in the orbit to clarify biomechanical consequences of ON traction during adduction.

Bony Orbital Decompression in Patients with High Myopia and Pseudoexophthalmos

INTRODUCTION

High myopic eyes grow in length (> 0.35 mm/dpt) more than in height and width leading to a disturbing unilateral exophthalmos in patients with anisomyopia and - more rarely - a bilateral exophthalmos in high myopia affecting both eyes. Secondary consequences are sicca symptoms and painful eye mobility due to a large bulbus in a too small bony orbit. The aim of the work was to evaluate the effectiveness of bony orbital compression in cases of high myopia.

MATERIAL AND METHODS

Four patients underwent bony orbital decompression between the years 2012 and 2019. Two of the patients received lateral and two of them balanced (medial endonasal endoscopic and lateral) decompression. The decompression effect, complications and the influence of decompression on eye position and motility were evaluated.

RESULTS

Significant decompression effect was achieved in all patients. As a result, symmetry was restored in all unilaterally affected patients. No complications occurred. The lateral decompression had a positive effect on the preexisting convergent strabismus (reduction of the "eso" position, neutral to the vertical deviation). The carefully dosed medial decompression did not lead to any change of the horizontal position in one patient and in the other exotropic patient it resulted in a 10 pdpt of "exo" reduction without developing an "eso" position.

DISCUSSION

The bony orbital decompression provides a sufficient decompression effect in the four patients to reduce the myopic pseudoexophthalmos. The alignment anomalies associated with a high myopia ("heavy eye") was favourably influenced by the lateral decompression.