Clinical Parameters Reflecting Globe/orbit Volume Imbalances in Japanese Acquired Esotropia Patients with High Myopia but without Abduction Limitations.

In high myopia, eye dislocation due to increased globe volume or tight orbital volume causes acquired esotro-pia. GOR (globe/orbit volume ratio), an indicator of the degree of progression of this pathology, was investi-gated the relationships among easily obtained clinical parameters. In this retrospective study, 20 eyes from 10 acquired esotropia patients with high myopia but without abduction limitations were examined. The mean age of the patients was 63.7 ± 8.2 years (mean ± standard deviation). Volumes were measured on the three-dimen-sional fast imaging employing steady-state acquisition magnetic resonance imaging images using the vol-ume-measurement function. Correlations between GOR and the displacement angle of the globe (DA), axial length (AL), and equatorial diameter (ED) were investigated. Mean DA, AL, ED, and GOR values were 107.5 ± 8.5°, 28.86 ± 1.92 mm, 25.00 ± 1.16 mm, and 0.36 ± 0.05, respectively. Only AL was correlated with GOR (p < 0.0001, R2 = 0.6649); DA (p = 0.30, R2 = 0.0633) and ED (p = 0.91, R2 = 0.0008) were not. AL was the only clinically available parameter to indicate globe/orbit volume imbalances in acquired esotropia with high myopia but without abduction limitation. AL may be important for the clinical assessment of the progression of this pathology.

Risk factors for excessive postoperative exo-drift after unilateral lateral rectus muscle recession and medial rectus muscle resection for intermittent exotropia.

BACKGROUND: To detect significant factors associated with excessive postoperative exo-drift in young patients with intermittent exotropia who had undergone unilateral lateral rectus muscle recession and medial rectus muscle resection. METHODS: We retrospectively examined the records of 64 consecutive patients < 18 years old who underwent surgery between April 2004 and December 2011. We sought risk factors for excessive postoperative exo-drift among patients' demographic and clinical characteristics using univariate and multivariable linear regression analysis. RESULTS: Younger patients (P = 0.007), and those with larger preoperative exo-deviation at distance (P = 0.033), a lower incidence of peripheral fusion at distance (P = 0.021) or a greater postoperative initial eso-deviation (P = 0.001), were significantly more likely to have an excessive postoperative exo-drift (> 20 prism diopters). Univariate analysis revealed significant associations between excessive postoperative exo-drift and age at surgery (P = 0.004), preoperative exo-deviation at distance (P = 0.017) and postoperative initial eso-deviation at distance (P < 0.001). Multivariable linear regression analysis showed that postoperative initial eso-deviation at distance (P = 0.008) was significantly associated with postoperative exo-drift. CONCLUSIONS: Postoperative exodrift in unilateral RR is predicted by the initial postoperative eso-deviation, which may offset the overcorrection. However, the exo-drift is greater in cases with a large preoperative exo-deviation and/or at a younger age, and should be followed carefully.

Formulas to Estimate Appropriate Surgical Amounts of Unilateral Recession-Resection in Intermittent Exotropia with Distance-Near Disparity.

The purpose of this study was to derive new formulas to provide an optimal surgical procedure and optimal amount of recession-resection (RR) surgery in intermittent exotropia (IXT) with a disparity in angle of deviation depending on the fixation distance. The records of 117 consecutive patients with IXT who underwent RR surgery between March 2008 and December 2011 at Okayama University Hospital were retrospectively examined. Multivariable linear regression analysis was performed using the observed corrective angle of deviation at distance or near fixation as the dependent variable, and amounts of lateral rectus muscle (LR) recession (mm) and medial rectus muscle (MR) resection, and age at surgery (years) as independent variables. Two simultaneous formulas were derived: corrective angle of deviation at distance fixation (°)=1.8×recession (mm)+1.6× resection (mm)+0.15×age (years)-6.6, and corrective angle at near fixation (°)=1.5×recession (mm)+1.7× resection (mm)+0.18×age (years)-3.8. Comparisons of coefficient values of the formulas between distance and near fixation revealed that LR recession was more affected by the corrective angle in distance than near fixation. MR resection was more affected at near than distance fixation. We found that our new formulas estimated the appropriate amount of unilateral RR surgery.

Magnetic resonance imaging findings of age-related distance esotropia in Japanese patients with high myopia.

PURPOSE: This study aimed to investigate the characteristics of the extraocular muscles and the orbital connective tissue pulleys in Japanese patients with age-related distance esotropia (ARDE) and high myopia using magnetic resonance imaging (MRI). METHODS: This was a retrospective case-series study. High-resolution coronal MRI scans of 12 orbits were obtained in 6 patients with ARDE and high myopia (age range: 51-69 years). We analyzed the images to determine the positions of the rectus muscle pulleys relative to the center of the globe, the integrity of the lateral rectus-superior rectus muscle (LR-SR) band, and the LR angle (the angle between the major axis of the LR and the vertical plane). RESULTS: The distance esotropia ranged from 4 to 25∆, and 3 cases exhibited vertical deviations. The mean (±standard deviation (SD)) axial length was 28.5 (± 1.6) mm. The mean positions of the medial rectus muscle pulley and LR pulley were 1.3 mm inferior and 1.4 mm inferior, respectively, to those seen in the normal control group in our previous study (P = 0.002 and P = 0.05, respectively). All 12 orbits had abnormal elongated LR-SR bands, and 8 orbits (67%) displayed ruptured LR-SR bands. The LR angle (mean±SD; 18.8° ± 8.5°) increased significantly with the inferior displacement of the LR pulley (R2 = 0.77, P = 0.0002). CONCLUSIONS: Inferior displacement of the LR pulley and abnormal LR-SR bands were seen in Japanese ARDE patients with high myopia, as was found in ARDE patients without high myopia. The LR angle might be useful for judging the degree of LR pulley displacement.

Twist Knot: A New Sliding Noose in Adjustable Suture Strabismus Surgery.

To permit noose movement without fraying the sutures following strabismus surgery, we designed a new sliding noose, the "twist knot" and investigated its advantages and disadvantages. We measured the tensile strength required to move the twist knot in a tightly tied state (134±19 gf) and in a loosened state (21±7 gf), and that required to move the conventional sliding noose in a tightly tied state (48±14 gf), and used the Kruskal-Wallis test to compare them. A significant difference was observed among the three tensile strengths (p<0.001). The twist knot technique allowed easy sliding without the multifilament braided suture becoming frayed and a knot to be firmly fixed without slipping. However, if the 2 strings of the pole sutures exit from the sclera at 2 widely separated positions, the sliding noose may become slack. Therefore, the distance between the pole sutures should be small. The simple twist knot technique was found to be an effective approach following adjustable surgery of strabismus.

Lights-out Surgery for Strabismus Using a Heads-Up 3D Vision System.

During strabismus surgery using illumination from a light source, patients complain of photophobia. The NGENUITYⓇ (Alcon) system is equipped with a high-dynamic-range (HDR) camera. A 4K display viewed by wearing circularly polarized glasses provides clear three-dimensional images of the operative field. A light source is usually required for surgeries of the anterior segment (including strabismic surgery), but the digital processing function of the NGENUITYⓇ system allows image display in relatively dark regions even without a light source. We devised a novel 'lights-out' surgery that does not use a microscope's light source, and we examined the usefulness of this technique in 2 cases of strabismic surgery. We performed strabismus surgery using the NGENUITYⓇ system in two patients between January and June 2018. The HDR function was used, and the aperture was opened to the maximum while the gain was adjusted. Surgery was conducted without using the microscope's light source. We report the 2 cases' results and evaluate the novel method. The surgeries were performed without problem even though the microscope's light source was not used. The patients' photophobia was alleviated. Lights-out surgery is a potentially useful modality for strabismus surgery.

Congenital Multiple Ocular Motor Nerve Palsy Complicated by Splitting of the Lateral Rectus Muscle.

We report a case of congenital multiple ocular motor nerve palsy combined with splitting of the lateral rectus muscle (LR). A 59-year-old Japanese female was investigated for worsening esotropia after corrective surgery. She presented with left hypertropia (35Δ) and esotropia (45-50Δ). Orbital magnetic resonance imaging (MRI) showed reduced belly sizes in the superior rectus, inferior rectus, and superior oblique muscles and splitting of the LR, extending from the origin to the belly, in the left eye. Splitting of the LR belly was detected on MRI in a case of congenital multiple ocular motor nerve palsy.

Effects of vertical muscle surgery on differences in the orientation of Listing's plane in patients with superior oblique palsy.

BACKGROUND: Although scleral search coils are widely and accurately used for the measurement of Listing's plane in both eyes, they require specialized equipment and are invasive. In this study, we describe a convenient and less invasive method that uses a synoptometer to analyze the differences in orientation of Listing's plane (difLP), and the effects of vertical muscle surgery on the difLP tilt in patients with superior oblique palsy (SOP). METHODS: Seventeen patients with unilateral congenital SOP (CSOP) and four patients with unilateral acquired SOP (ASOP) who had not undergone any strabismus surgeries were examined. Cyclodeviations of 13 vertical and horizontal gaze points within 30° were measured with a synoptometer, and the difLP tilts in the yaw and pitch planes were analyzed before and after vertical muscle surgery. RESULTS: The difLP tilt in the CSOP patients was significantly tilted nasally (p = 0.02) and forward on the lower side (p = 0.001), whereas that in ASOP patients tended to tilt temporally (p = 0.15). Ipsilateral inferior oblique recession (IOR) performed in seven CSOP patients tended to improve the difLP tilt in both the yaw (p = 0.07) and pitch (p = 0.09) planes, whereas contralateral inferior rectus recession (IRR) performed in three CSOP patients significantly improved the difLP tilt in the pitch plane (p = 0.015). The mean excyclodeviations in the 13 gaze points were significantly improved with both procedures (p < 0.0001 for both). CONCLUSIONS: The difLP tilt in the SOP patients could be analyzed with a convenient and less invasive method using a synoptometer, and dissimilar difLP tilts were confirmed in the ASOP and CSOP patients. The results of this study suggest that both IOR and IRR are reasonable treatments for improving the difLP tilt in CSOP patients. IOR should be selected for patients with a steep preoperative difLP tilt to the nasal side, whereas IRR should be selected for patients with a gentle preoperative difLP tilt.

Analysis of temporal changes in thickness from conjunctiva to sclera after plication of the medial rectus muscle measured by anterior segment optical coherence tomography.

PURPOSE: We evaluated long-term changes in conjunctival bulge after medial rectus muscle (MR) tightening using the plication method. STUDY DESIGN: Retrospective and observational. METHODS: Patients who underwent MR plication for exotropia from December 2016-March 2020 at Okayama University Hospital were included. Thirty two eyes of 27 patients were enrolled. The thickness from the conjunctiva to sclera (TCS) at the limbus and insertion sites were measured using anterior segment optical coherence tomography preoperatively and 1 month, 4 months, and 12 months postoperatively. Correlations between the 1- and 12 month postoperative TCS and amount of MR tightening were analyzed. RESULTS: Preoperative and 4 month postoperative TCS at the limbus site were not significantly different (P=0.07). The 12 month postoperative TCS at the insertion site was significantly thinner than at 1 month postoperative (P<0.01), although significantly thicker than the preoperative TCS (P<0.01). No significant correlations were found between the amount of MR tightening (in mm) and 1- or 12 month postoperative TCS at the limbus (P=0.62 and P=0.98, respectively) and insertion (P=0.50 and P=0.24, respectively) sites. CONCLUSION: The TCS at the insertion site peaked at 1 month postoperatively, continued to decrease for longer than 4 months postoperatively, continuing until 12 months postoperatively. The TCS at the insertion site 12 months postoperatively is thicker than preoperatively. The TCS at both the limbus and insertion sites was not related to the amount of medial rectus muscle tightening.

Shape analysis of rectus extraocular muscles with age and axial length using anterior segment optical coherence tomography.

PURPOSE: This study aimed to evaluate the shape of the extraocular muscles (EOMs) in normal subjects using the en-face images of anterior segment optical coherence tomography (AS-OCT). The EOM insertion and the direction of the muscle fibers were investigated. SUBJECTS AND METHODS: A total of 97 healthy normal subjects (194 eyes) at Okayama University Hospital (age, 47.1±21.5 years; range, 8-79 years) participated in the study. A series of 256 tomographic images of the rectus EOMs were captured using the C-scan function of the AS-OCT (CASIA2, TOMEY Co., Japan), and the images were converted to en-face images in multi-TIFF format. The anterior chamber angle to EOM insertion distance (AID) and the angle of the muscle fibers from the insertion site (angle of muscles) were measured from the images. The correlations of AID and angle of muscles with age and axial length were investigated and evaluated. RESULTS: AID and angle of muscles were significantly correlated with age or axial length in some EOMs. The AIDs of medial rectus (MR) (P = 0.000) and superior rectus (SR) (P = 0.005) shortened with age. The AIDs of MR (P = 0.001) and inferior rectus (IR) (P = 0.035) elongated with axial length, whereas lateral rectus (LR) (P = 0.013) shortened. The angles of MR (P = 0.001) and LR (P = 0.000) were found to have a more downward direction toward the posterior in older subjects. CONCLUSION: En-face images can be created by AS-OCT, and the shape of the EOMs in normal subjects using these image measurements was available. With the ability to assess the EOMs, AID and angle of muscles are expected give useful information for treating and diagnosing strabismus-related diseases.

Displacement of the rectus muscle pulleys simulating superior oblique palsy.

PURPOSE: To investigate the structural basis of three cases of apparent superior oblique (SO) palsy caused by extraocular muscle (EOM) pulley heterotopy. METHODS: Three subjects were diagnosed as having decompensated idiopathic left SO palsy on the basis of misalignment in diagnostic gaze positions, response to the head tilt test, and results of the Hess screen test. Magnetic resonance imaging of the orbits in coronal planes was used to determine SO muscle size and contractility and to define the rectus EOM pulley locations. Orbit 1.8 computer simulation was performed for each subject by using measured rectus pulley locations. Simulated binocular alignment was compared with the measurements. RESULTS: The maximal SO cross sections of both eyes of each subject were similar, and exhibited similar contractile thickening from supraduction to infraduction. The superior rectus muscle pulleys in three eyes exhibited significant temporal displacement, while the lateral rectus muscle pulleys in five eyes and the medial rectus muscle pulleys in two eyes were displaced significantly inferiorly compared with published norms. Simulations based on observed pulley position abnormalities alone predicted measured Hess screen data better than did simulations incorporating SO weakness, either alone or combined with other structural abnormalities. CONCLUSIONS: Heterotopy of the rectus EOM pulleys may be associated with cyclovertical strabismus that simulates SO palsy.

Superior oblique muscle layers in monkeys and humans.

PURPOSE: Rectus and the inferior oblique extraocular muscles (EOMs) consist of orbital layers (OLs), inserting on connective tissues, and global layers (GLs), inserting on the sclera. This study was performed to clarify the anatomic relationships of the corresponding layers of the superior oblique (SO) muscle. METHODS: Two whole human and two monkey orbits were serially sectioned en bloc at 10-mum thickness in the coronal plane and stained for collagen with Masson's trichrome and for elastin with van Gieson's stain. The SO muscles of one human and one monkey were sectioned longitudinally. The structure of the SO muscle was examined by light microscopy, and muscle fibers in the OL and GL of selected sections were counted. RESULTS: The deep SO muscle consisted of a central GL contiguous with the tendon, surrounded coaxially by a peripheral OL inserting on the SO sheath posterior to the trochlea. The maximum number of SO fibers was 14,400 to 19,200 in the human and 7,000 to 7,400 in the monkey. In the monkey, approximately 60% of total fibers were in the GL, and 40% in the OL. The SO sheath was in mechanical continuity with the superior rectus pulley. CONCLUSIONS: The primate SO has a substantial OL configured to contribute to positioning the superior rectus pulley in the coronal plane. Whereas the direction of application of the SO's GL force is determined by the rigid trochlea, the SO's OL influences the direction of application of rectus EOM forces. This insight extends the concept of active control of pulley positions to include a contribution from the SO muscle.

Displacement of rectus muscle pulleys by torsional muscle surgery for treatment of full macular translocation-induced incyclotropia.

PURPOSE: To elucidate the coronal plane locations of extraocular muscle (EOM) pulleys following torsional muscle surgery. DESIGN: Case report. METHODS: A 76-year-old man underwent advancement of the anterior part of the inferior oblique muscle to treat full macular translocation-induced incyclotropia. Postoperatively, magnetic resonance imaging was used to obtain contiguous, 2-mm-thick coronal orbital images. On each MRI image, the cross-sectional area and center of the EOM was computed, and all rectus EOM positions were translated to the coordinate origin at the area centroid of the globe at the level of pulleys. RESULTS: The superior rectus pulley was displaced temporally, and the lateral rectus pulley was displaced inferiorly more than 2 SD from normal subjects. Coronal plane locations of EOM pulleys of the ipsilateral eye showed extorsion compared with that of the contralesional eye. CONCLUSIONS: Torsional muscle surgery causes an extorsional shift of the superior and lateral rectus pulleys.

Quantitative analysis of the structure of the human extraocular muscle pulley system.

PURPOSE: Extraocular muscle (EOM) paths are constrained by connective tissue pulleys serving as functional origins. The quantitative structural features of pulleys and their intercouplings and orbital suspensions remain undetermined. This study was designed to quantify the composition of EOM pulleys and suspensory tissues. METHODS: Five human orbits, ages 33 weeks gestation to 93 years, were imaged intact by magnetic resonance (MRI), serially sectioned at 10 micro m thickness, and stained for collagen, elastin, and smooth muscle (SM). With MRI used as a reference, digital images of sections were geometrically corrected for shrinkage and processing deformations, and normalized to standard normal adult globe diameter. EOM pulleys, interconnections, suspensory tissues, and entheses were quantitatively analyzed for collagen, elastin, and SM thickness and density. RESULTS: Rectus and inferior oblique pulleys had uniform structural features in all specimens, comprising a dense EOM encirclement by collagen 1 to 2 mm thick. Elastin distribution varied, but was greatest in the orbital suspension of the medial rectus pulley and in a band from it to the inferior rectus pulley. This region corresponded to maximum SM density. Structural features of pulleys, intercouplings, and entheses were similar among specimens. The major mechanical couplings to the osseous orbit were near the medial and lateral rectus pulleys. CONCLUSIONS: Quantitative analysis of structure and composition of EOM pulleys and their suspensions is consistent with in vivo MRI observations showing discrete inflections in EOM paths that shift predictably with gaze. Focal SM distributions in the suspensions suggest distinct roles in stiffening as well as shifting rectus pulleys.

Active pulleys: magnetic resonance imaging of rectus muscle paths in tertiary gazes.

PURPOSE: The orbital layer of each rectus extraocular muscle (EOM) inserts on connective tissue, and the global layer inserts on the eyeball. The active-pulley hypothesis (APH) proposes that a condensation of this connective tissue constitutes a pulley serving as the functional origin of the rectus EOM, and that this pulley makes coordinated, gaze-related translations along the EOM axis to implement a linear ocular motor plant. This study was designed to measure gaze-related shifts in EOM pulley locations. METHODS: Magnetic resonance imaging (MRI) was performed in eight normal volunteers in 2-mm thickness coronal planes perpendicular to the orbital axis for nine cardinal gaze directions. Intravenous gadodiamide contrast was administered to define EOM tendons anterior to the globe equator. Paths of EOMs, defined by their area centroids, were transformed into an oculocentric coordinate system. Sharp inflections in EOM paths in secondary and tertiary gaze positions defined pulley locations which were then correlated with gaze direction and compared with theoretical predictions. RESULTS: Rectus pulley positions were consistent with a central primary position. In tertiary gaze positions, each of the four rectus pulleys translated posteriorly with EOM contraction and anteriorly with EOM relaxation by a significant (P < 0.02) amount predicted by the APH, but more than 100 times greater than the translation predicted by a passive pulley model. CONCLUSIONS: The APH prediction of coordinated anteroposterior shifting of EOM pulleys with gaze is quantitatively supported by changes in EOM path inflections among tertiary-gaze positions. Human rectus pulleys move to shift the ocular rotational axis to attain commutative behavior of the ocular motor plant.

Impaired vertical phoria adaptation in patients with cerebellar dysfunction.

PURPOSE: To determine whether phoria adaptation to a vertical prism disparity is altered in patients with cerebellar dysfunction. METHODS: With a computer-aided haploscope, adaptive responses of fusion-free eye position to a 10- or 30-minute period was measured in subjects wearing a 3-prism diopter vertical prism over one eye. Thirteen patients with well-documented cerebellar diseases who did not have manifest ocular misalignment or limited versional eye movement and age-matched healthy subjects participated. RESULTS: The mean +/- SD percentage of vertical phoria adaptation was 13% +/- 22% and 20% +/- 16% for the 10- and 30-minute adaptations, respectively. These levels were significantly smaller than the respective ones in the age-matched control group (P < 0.001, repeated measures MANOVA). Seven (54%) of 13 patients, including two with genetically confirmed pure cerebellar lesions (spinocerebellar ataxia type 6), showed markedly reduced responses to both the 10- and 30-minute adaptations. In all three patients with acute cerebellar ataxia, the adaptive response was improved at the same time as remission of cerebellum-associated neurologic deficits. CONCLUSIONS: Phoria adaptation to vertical binocular disparity is frequently impaired in patients with cerebellar dysfunction. These results bolster the hypothesis that phoria adaptation is a cerebellar-dependent response.

A 12-year, prospective study of extraocular muscle imaging in complex strabismus.

INTRODUCTION: Diagnostic imaging by magnetic resonance imaging (MRI) or computed x-ray tomography (CT) has become the standard of care in many medical fields. Clinical imaging of the extraocular muscles (EOMs) can now provide insight into some causes of strabismus, in some cases challenging traditional concepts of etiology and suggesting alternative treatments. METHODS: Between 1990 and 2001, 62 orthotropic volunteers and 261 strabismic patients underwent orbital imaging under a prospective protocol. Surface coil MRI was performed with fixation control with slice thickness of 1.5 to 3 mm; CT was performed with 1-mm slice thickness. Images were correlated with ophthalmological examinations. RESULTS: MRI was performed in 267 and CT in 56 subjects. Comparison with normal orbits commonly demonstrated abnormalities of EOM size or location in strabismic patients. These included absence (5 patients) or atrophy (33 patients) of the superior oblique (SO) muscle in SO palsy; abnormalities of the trochlea or SO tendon in Brown's syndrome (8 patients); heterotopy of the rectus pulleys associated with incomitant strabismus (46 patients), including instability of pulleys (9 patients); trauma to rectus EOMs (16 patients); atrophy of the lateral rectus (10 patients), inferior rectus (4 patients), medial rectus (4 patients), superior rectus (4 patients), and inferior oblique (1 patient) muscles; and EOMs disinserted by scleral buckles (3 patients). EOM abnormalities correlated closely with clinically abnormal patterns of ocular motility. CONCLUSIONS: With the appropriate technique, EOM imaging is a valuable adjunct in clinical evaluation of complex strabismus. Because imaging can provide unique information unavailable from the clinical examination alone, it should be performed when indicated to evaluate patients with strabismus more complex than concomitant esotropia and exotropia.

[Vertical vergence adaptation in cases of superior oblique palsy].

PURPOSE: To investigate the characteristics of vertical adaptation (VA) in superior oblique muscle palsy (SOP). SUBJECTS AND METHODS: VA was examined in 15 patients with unilateral congenital SOP, 7 patients with unilateral acquired SOP, and 35 normal volunteers. An adaptive change in the fusion-free ocular alignment, VA, was measured with a computer-aided mirror haploscope. The fusion-free ocular alignment was measured before inserting a 3 prismdiopter vertical prism, immediately after inserting the prism, and at 10 minutes and 30 minutes after insertion. We investigated VA gain, age, vertical fusional range, response of prism adaptation test (PAT), and superior oblique muscle atrophy in magnetic resonance imaging (MRI). RESULTS: The VA gain (mean +/- standard deviation, %) at 30 minutes in congenital, acquired, and normal groups was 86 +/- 53, 34 +/- 23 and 58 +/- 16, respectively. The mean of the VA gains at 30 minutes in the congenital group was greatest, and that in the acquired group was least(p < 0.01). In the congenital group there was a correlation between VA gain and response of PAT (p = 0.02, r = 0.60). The VA gain did not significantly correlate with age, vertical fusional range, or muscle atrophy. CONCLUSION: The VA gain observed in congenital SOP was greater than that of acquired SOP, and affected the response of PAT.

Effects of oblique muscle surgery on the rectus muscle pulley.

PURPOSE: To determine the position of rectus muscle pulleys in Japanese eyes and to evaluate the effect of oblique muscle surgery on rectus muscle pulleys. METHODS: Quasi-coronal plane MRI was used to determine area centroids of the 4 rectus muscles. The area centroids of the rectus muscles were transformed to 2-dimensional coordinates to represent pulley positions. The effects of oblique muscle surgery on the rectus muscle pulley positions in the coronal plane were evaluated in 10 subjects with cyclovertical strabismus and, as a control, pulley locations in 7 normal Japanese subjects were calculated. RESULTS: The mean positions of the rectus muscle pulleys in the coronal plane did not significantly differ from previous reports on normal populations, including Caucasians. There were significant positional shifts of the individual horizontal and vertical rectus muscle pulleys in 3 (100%) patients with inferior oblique advancement, but not in eyes with inferior oblique recession and superior oblique tendon advancement surgery. The surgical cyclorotatory effect was significantly correlated with the change in the angle of inclination formed by the line connecting the vertical rectus muscles (p = 0.0234), but weakly correlated with that of the horizontal rectus muscles. CONCLUSIONS: The most important factor that affects the pulley position is the amount of ocular torsion, not the difference in surgical procedure induced by oblique muscle surgery.

Splitting of the extraocular horizontal rectus muscle in congenital cranial dysinnervation disorders.

PURPOSE: To analyze the horizontal rectus extraocular muscles (EOMs) by orbital magnetic resonance imaging (MRI) in patients with congenital cranial dysinnervation disorders that arises from abnormal development of cranial nerve nuclei or their axonal connections. DESIGN: Case series, retrospective analysis. METHODS: The morphology of the horizontal rectus EOMs was analyzed in orbital MRI on 4 patients with congenital oculomotor palsy, 26 with congenital superior oblique palsy, and five with Duane syndrome. Orbital imaging was performed by 1.5 tesla (T) and 3T MRI, and quasi-coronal and sagittal images perpendicular and parallel to the long axis of the orbit were obtained at slice thicknesses of 3 and 2 mm. RESULTS: The horizontal rectus EOMs were split in 4 of the 35 patients (11%). Splitting was observed in 2 of the five patients (40%) with Duane syndrome, one of the 26 patients (4%) with congenital superior oblique palsy, and 1 of the 4 patients (25%) with oculomotor palsy, but in none of the 6 normal subjects and 12 patients with acquired cranial nerve palsy. CONCLUSION: Since splitting of the horizontal rectus EOMs was noted in patients with congenital dysinnervation disorders, including Duane syndrome, Sevel's theory that the horizontal rectus EOMs develop from the superior and inferior mesodermal complexes is considered to be reasonable.