Extraocular Muscle Size Research Articles

Efficacy and Systemic Effects of a Single Deep Orbital Triamcinolone Injection for Thyroid Eye Disease.

Orbital steroid injections offer a potential therapeutic avenue for managing Thyroid Eye Disease (TED). This study aimed to assess the effectiveness and potential systemic impacts of a single deep orbital triamcinolone injection in TED patients. In a prospective investigation conducted from January 2021 to March 2023, patients diagnosed with TED were enrolled. Inclusion criteria encompassed a Clinical Activity Score (CAS) of ≥3, extraocular muscle inflammation, and upper eyelid retraction. A total of 1 mL of triamcinolone acetonide (40 mg/mL) was administered posterior to the orbital septum at both the medial and lateral aspects of both the upper and lower eyelids. Parameters, including CAS, margin-reflex distances (MRD1 and MRD2), intraocular pressure (IOP), ocular motility (Hess area ratio [HAR%]), exophthalmometry, extraocular muscle size, and blood and urinary indices, were evaluated before and at 2 and 4 weeks after a single injection. Analysis included 28 patients (23 women, 5 men; mean age (SD): 38.7 (11.1) years), representing 56 eyes. Following the injection at 4 weeks, the mean CAS and MRD1 significantly decreased by 2 points and 0.8 mm, respectively. There was a 4.5% increase in HAR%, and extraocular muscle size decreased by 4 to 15.3 mm². Neutrophil count, C-reactive protein, and thyroid antibodies significantly decreased. No severe adverse ophthalmic or systemic effects, including IOP increases or liver damage, were observed. Bilateral single orbital triamcinolone injections provided relief from TED symptoms through both direct effects on orbital soft tissue and systemic effects by decreasing antibody reactions.

Echographic characterization of extraocular muscles in pediatric patients with thyroid dysfunction

ABSTRACT Purpose To characterize the size of extraocular muscles (EOMs) in a pediatric population with thyroid dysfunction using orbital echography. Methods Patients under age 18 with thyroid dysfunction who presented to an academic ophthalmology department from 2009 to 2020 and received orbital echography were included in this IRB-approved retrospective study. Data collected included age, clinical activity score (CAS), thyroid stimulating immunoglobulin (TSI), and extraocular recti muscle thickness on echography. Patients were organized into three age cohorts, after which statistical analysis compared recti measurements to previously reported normal ranges. Results Twenty patients with thyroid dysfunction were included. When comparing average recti muscle thicknesses of study patients to those of previously published normal children in similar age ranges, the levator-superior rectus complex was significantly increased in all age groups of children with thyroid dysfunction (p-values = <.004), and the levator-superior rectus complex was most frequently enlarged compared to published normal values (78% of eyes). CAS was not correlated with EOM size in the youngest group (5–10 years old, p-values >.315) but was significantly correlated in older groups (11–17 years old, p-values <.027). TSI was not correlated with EOM size in any group (p-values >.206). Conclusions Echographic reference ranges for EOMs in children with thyroid dysfunction were established. There are increased rates of levator-superior rectus complex enlargement in children with TED compared to adults with TED, and EOM size is correlated with CAS in children older than 10 years. Though limited, these findings may serve as an additional tool for ophthalmologists to ascertain disease activity in pediatric patients with thyroid dysfunction.

Semantic Segmentation of Extraocular Muscles on Computed Tomography Images Using Convolutional Neural Networks.

Computed tomography (CT) imaging of the orbit with measurement of extraocular muscle size can be useful for diagnosing and monitoring conditions that affect extraocular muscles. However, the manual measurement of extraocular muscle size can be time-consuming and tedious. The purpose of this study is to evaluate the effectiveness of deep learning algorithms in segmenting extraocular muscles and measuring muscle sizes from CT images. Consecutive CT scans of orbits from 210 patients between 1 January 2010 and 31 December 2019 were used. Extraocular muscles were manually annotated in the studies, which were then used to train the deep learning algorithms. The proposed U-net algorithm can segment extraocular muscles on coronal slices of 32 test samples with an average dice score of 0.92. The thickness and area measurements from predicted segmentations had a mean absolute error (MAE) of 0.35 mm and 3.87 mm2, respectively, with a corresponding mean absolute percentage error (MAPE) of 7 and 9%, respectively. On qualitative analysis of 32 test samples, 30 predicted segmentations from the U-net algorithm were accepted while 2 were rejected. Based on the results from quantitative and qualitative evaluation, this study demonstrates that CNN-based deep learning algorithms are effective at segmenting extraocular muscles and measuring muscles sizes.

Extraocular Muscle Enlargement in Growth Hormone-Secreting Pituitary Adenomas.

While Graves disease is the most common cause of extraocular muscle enlargement, case reports have also associated growth hormone-secretory pituitary adenomas with this same phenomenon. We investigated the prevalence and response to treatment of extraocular muscle enlargement in patients with growth hormone-secretory pituitary adenomas. We retrospectively reviewed extraocular muscle sizes using MR imaging in patients with growth hormone-secretory pituitary adenomas who underwent a transsphenoidal surgical resection compared with a matched control group with nonsecretory pituitary adenomas. Descriptive and comparative statistics were used to evaluate patient characteristics and extraocular muscle sizes between the 2 groups. We identified 16 patients who presented with growth hormone-secreting pituitary adenomas and underwent transsphenoidal surgical resection from 2010 to 2019. The average diameter of the extraocular muscle at the time of diagnosis for the group with growth hormone-secretory pituitary adenomas was larger than that in the control group (4.7 versus 3.8 mm, P < .001). Nine patients achieved insulin-like growth factor 1 level normalization at a median of 11.5 months before their most recent MR imaging evaluation. The average size of the extraocular muscles of patients who achieved a normalized insulin-like growth factor 1 was smaller compared with those that did not (difference, 0.7 mm; 95% CI, 0.3-1.2 mm; P < .001), approaching the size of extraocular muscle in the control group. We describe a high prevalence of extraocular muscle enlargement in patients with growth hormone-secreting pituitary adenomas. Additionally, we note that the size of extraocular muscles decreased with associated improvement in the biochemical control of acromegaly.

Diplopia after Isolated Inferior Orbital Wall Fracture According to the Computed Tomography Findings

Purpose: To investigate the postoperative changes in diplopia and evaluate factors that affect diplopia after isolated inferior orbital wall fracture.Methods: A retrospective study was conducted on 200 patients who underwent reconstruction surgery for isolated inferior orbital wall fracture between March 2001 and December 2020. Diplopia was categorized into peripheral, central, and full-degree types based on the history and binocular single vision. The natural course of diplopia was analyzed pre-operatively and at 1 day, 6 weeks, and 6 months postoperatively. We analyzed the orbital computed tomography images to determine fracture size (small, medium, or large), fracture site (anterior, middle, posterior, or mixed), extraocular muscle (EOM) size (swelling or deformity), EOM site (incarcerated or prolapsed), and EOM tenting.Results: Diplopia was seen in 144 out of 200 patients (72.0%) before surgery; peripheral diplopia was seen in 57 patients (39.6%), central diplopia in 46 (24.3%), and full-degree diplopia in 20 (13.9%). Pre-operative diplopia differed according to the pre-operative limitation of range of motion (LOM) (p &lt; 0.001) and EOM site (p = 0.022). Pre-operative diplopia type differed according to the LOM direction (p = 0.018) and EOM size (p = 0.020). Diplopia persisted in 33 patients (16.5%) 6 months after the surgery. Recovery was faster in patients with peripheral diplopia compared to those with central or full-degree diplopia.Conclusions: The presence of diplopia was associated with the pre-operative LOM and EOM site but the type of diplopia was associated with LOM direction and EOM size. These factors can be used to predict the progression of diplopia in patients with isolated inferior orbital wall fracture.

Lateral Rectus Muscle Expands More Than Medial Rectus Following Maximal Deep Balanced Orbital Decompression.

It has been reported that extraocular muscles can enlarge following orbital decompression in thyroid eye disease. In this article, the authors studied the changes in extraocular muscles size following maximal deep lateral and medial balanced decompression in a large sample of thyroid eye disease patients. Imaging data were reviewed preoperatively and postoperatively. Radiologic proptosis was assessed. Maximal axial muscle width of the medial and lateral recti was measured. Data from 48 consecutive patients (75 orbits) were included. There was a significant increase in the width of both the lateral and medial recti after decompression (p < 0.01). The mean (standard deviation [SD]) change was less for the medial rectus (0.7 mm) than for the lateral (2.7 mm). This difference was significant (p < 0.01). For the lateral rectus, 80% of all decompression surgeries were associated with an increase in width of >1 mm. Mean (SD) proptosis reduction was 8.2 mm (3.4 mm). These results suggest that the extraocular muscles enlarge in the most deep lateral wall decompressions. For decompression as performed in this article, expansion tends to be more commonly found and of a greater magnitude in the lateral rectus compared with medial.

Rectus Extraocular Muscle Size and Pulley Location in Concomitant and Pattern Exotropia

To determine whether rectus extraocular muscle (EOM) sizes and pulley locations contribute to exotropia, we used magnetic resonance imaging (MRI) to measure these factors in normal control participants and in patients with concomitant and pattern exotropia. Prospective case-control study. Nine patients with concomitant exotropia, 6 patients with pattern exotropia, and 21 orthotropic normal control participants. High-resolution surface-coil MRI scans were obtained in contiguous, quasicoronal planes. Rectus pulley locations were determined in oculocentric coordinates for central gaze, supraduction, and infraduction. Cross sections in 4 contiguous image planes were summed and multiplied by the 2-mm slice thickness to obtain horizontal rectus posterior partial volumes (PPVs). Rectus pulley locations and horizontal rectus PPVs. Rectus pulleys were located differently in patients with A-pattern, versus V- and Y-pattern, exotropia. The lateral rectus (LR) pulleys were displaced significantly superiorly, the medial rectus (MR) pulleys were displaced inferiorly, and the inferior rectus pulleys were displaced laterally in A-pattern exotropia. However, the array of all rectus pulleys was excyclorotated in V- and Y-pattern exotropia. The PPV of the medial rectus muscle was statistically subnormal by approximately 29% in concomitant, but not pattern, exotropia (P < 0.05). The ratio of the PPV of the LR relative to the MR muscles in concomitant exotropia was significantly greater than in control participants and those with pattern exotropia (P < 0.05). Abnormalities of EOMs and pulleys contribute differently in pattern versus concomitant exotropia. Abnormal rectus pulley locations derange EOM pulling directions that contribute to pattern exotropia, but in concomitant exotropia, pulley locations are normal, and relatively small medial rectus size reduces relative adducting force.

Correlation between Extraocular Muscle Size Measured by Computed Tomography and the Vertical Angle of Deviation in Thyroid Eye Disease.

The aim of this study was to investigate extraocular muscle (EOM) volume and cross-sectional area using computed tomography (CT), and to determine the relationship between EOM size and the vertical angle of deviation in thyroid eye disease (TED). Twenty-nine TED patients (58 orbits) with vertical strabismus were enrolled in the study. All patients underwent complete ophthalmic examination including prism, alternate cover, and Krimsky tests. Orbital CT scans were also performed on each patient. Digital image analysis was used to quantify superior rectus (SR) and inferior rectus (IR) muscle cross-sectional areas and volumes. Measurements were compared with those of controls. The correlation between muscle size and degree of vertical angle deviation was evaluated. The mean vertical angle of deviation was 26.2 ± 4.1 prism diopters. The TED group had a greater maximum cross-sectional area and EOM volume in the SR and IR than the control group (all p<0.001). Area and volume of the IR were correlated with the angle of deviation, but the SR alone did not show a significant correlation. The maximum cross-sectional area and volume of [Right IR + Left SR − Right SR − Left IR] was strongly correlated with the vertical angle of deviation (P<0.001). Quantitative CT of the orbit with evaluation of the area and volume of EOMs may be helpful in anticipating and monitoring vertical strabismus in TED patients.

Immunoglobulin G4–Related Disease of the Orbit: Imaging Features in 27 Patients

Immunoglobulin G4-related disease is a systemic fibroinflammatory process of unknown etiology, characterized by tissue infiltration by immunoglobulin G4 plasma cells. The purpose of this study was to retrospectively identify the spectrum of imaging features seen in immunoglobulin G4-related disease of the orbit. This study included 27 patients with biopsy-proved immunoglobulin G4-related disease of the orbit and either a CT or MR imaging of the orbits. These CT or MR imaging examinations were evaluated for the following: extraocular muscle size, extraocular muscle tendon enlargement, lacrimal gland enlargement, infiltrative process in the orbital fat (increased attenuation on CT or abnormal signal on MR imaging), infraorbital nerve enlargement, mucosal thickening in the paranasal sinuses, and extension of orbital findings intracranially. Extraocular muscles were enlarged in 24 of 27 (89%) patients, 21 (88%) bilaterally. In 32 of 45 (71%) affected orbits, the lateral rectus was the most enlarged muscle. In 26 (96%) patients, the tendons of the extraocular muscles were spared. Nineteen (70%) patients had lacrimal gland enlargement. Twelve (44%) patients had an infiltrative process within the orbital fat. Infraorbital nerve enlargement was seen in 8 (30%) patients. Twenty-four (89%) patients had sinus disease. Cavernous sinus or Meckel cave extension was seen in 3 (11%) patients. In patients with extraocular muscle enlargement, particularly when the tendons are spared and the lateral rectus is the most enlarged, and even more so when other noted findings are present, immunoglobulin G4-related disease should be a leading differential consideration, even over more commonly known etiologies of extraocular muscle enlargement.

Precise size evaluation of extraocular muscles using fat-suppressed fast T1-weighted gradient-recalled echo imaging and multiple gaze fixation targets

We studied the feasibility of the precise size measurement of extraocular muscles using fast magnetic resonance imaging sequences and gaze fixation targets. We recruited 20 healthy volunteers and optimized fat-suppressed fast T1-weighted gradient-recalled echo (FS T1-GRE) and single-shot fast spin-echo (SSFSE) imaging for evaluating extraocular muscles. With each eye at 40° abduction and adduction, we scanned the short-axis plane at the maximum diameter of the bilateral lateral and medial rectus muscles and measured the maximal cross-sectional area of the muscles during extension and contraction. We evaluated interobserver reproducibility and variability between the size measurements using the two MR sequences and the measurement reproducibility using FS T1-GRE imaging. The interobserver reproducibility in the muscle size measurements using FS T1-GRE and SSFSE imaging was excellent (r=0.93-0.94) and moderate to good (r=0.54-0.75), respectively. The interobserver variability was less with FS T1-GRE than SSFSE imaging (p<0.01). The reproducibility of the size measurement using FS T1-GRE was good to excellent (r=0.78-0.92). FS T1-GRE imaging with the subject staring at each of multiple targets is useful for evaluating precisely the size of extraocular muscles.

Correlation Between Extraocular Muscle Size and Motility Restriction in Thyroid Eye Disease

Evaluate the relationship between extraocular muscle (EOM) size, measured by computed tomography, and ocular motility in thyroid eye disease (TED). This case series is based on a retrospective review of the records of 54 patients (108 orbits) with TED. Main outcome measures included EOM size and degree of motility restriction. The average diameter of each rectus muscle was compared with published norms. Four subpopulations based on Age (< 40 or ≥ 40 years) and State of thyroid eye disease (active or stable) were studied. Versions were measured by the corneal light reflex method. The trend of muscle diameter versus motility restriction was evaluated. The average EOM diameter was greater than the norm in the study cohort and 4 subpopulations. The average diameter was largest in the Older and Active TED subpopulations. The inferior rectus and medial rectus were most frequently restricted in the study cohort and 4 subpopulations. The medial rectus had the strongest trend between increasing diameter and motility restriction, followed by the inferior rectus and the superior muscle group (comprised of the superior rectus and levator palpebrae superioris). However, there was a general lack of strong correlation between the diameter of the rectus muscles and their respective motility, especially in the Younger subpopulation. EOM diameters are larger and have more restricted motility in the Older and Active TED subpopulations. Contrary to prior publications, the correlation between EOM diameters and motility was weak, especially in the Younger subpopulation. These findings suggest that the pathophysiology of EOM enlargement is different based upon the age of the patient and the activity of the orbitopathy.

Effects of Elevated Thyroid Hormone on Adult Rabbit Extraocular Muscles

Human extraocular muscles (EOM) are preferentially susceptible to thyroid eye disease. Although the specific cause of this autoimmune disorder is unknown, it is often associated with elevated thyroid hormone levels. Thus, the effect of elevated thyroid hormone levels on cross-sectional area, myofiber size, satellite cells, and myosin heavy chain (MyHC) isoform expression was examined in adult rabbit EOMs, to determine how elevated thyroid hormone alters EOM biology. After 1 month of elevated thyroid hormone levels, the EOMs were removed and prepared for histologic examination. Total muscle mass, myofiber size, patterns of MyHC isoform expression, and the number of satellite cells were determined. Elevated thyroid hormone levels significantly decreased muscle mass, total number of myofibers, and mean cross-sectional area of the myofibers. Alterations in MyHC isoform expression were extremely complex, but several basic patterns emerged. The percentages of neonatal- and developmental-positive myofibers decreased in almost all EOM regions examined, and the percentages of slow-positive myofibers significantly increased. In contrast to normal EOMs, which retain a population of activated satellite cells throughout life, elevated thyroid hormone levels resulted in the virtual disappearance of MyoD-positive cells and a decrease in Pax7-positive cells. The reductions in EOM size, number of fibers expressing developmental and neonatal MyHC, and number of MyoD- and Pax7-positive satellite cells suggest that elevated thyroid hormone levels decrease the ongoing myofiber remodeling normally seen in the EOM. These catabolic changes have important implications for maintenance of function in the EOMs.

The Size of Extraocular Muscles Estimated by Computed Tomography in Patients Undergoing Orbital Wall Fracture Repair

Purpose: To determine the cross sections of extraocular muscles in patients with orbital fracture and to demonstrate a relationship among the cross sections, the size of orbital fracture, the soft tissue, and fat herniation and limitation of ocular movement. Methods: The study included 87 patients (87 eyes) with orbital fracture. The cross section was defined as multiplication of the long axis and short axis. The ratio of the cross section in normal and injured eyes was calculated at preoperative and postoperative periods. Results: The cross sections of all rectus muscles, except for the superior, increased in injured eyes and subsequently decreased postoperatively. After surgery, the cross sections of lateral and medial rectus muscles recovered to near normal but the inferior remained enlarged. The increased ratio of the short and long axis was significant but not the difference of the cross sections related to the short and long axis ratio. There was a preoperative difference between injured/normal cross section ratio in relation to the size of inferior fracture. There was postoperative normalization for the cross sections of inferior rectus muscles with the restrictive limitation due to inferior fracture. Conclusions: The cross sections increased mostly after orbital fracture and subsequently decreased postoperatively. There was a change in the cross section ratio with the size of inferior fracture at preoperative period but there was no change in the cross sections related to the restrictive or paralytic limitation, except for eyes with the restriction secondary to inferior fracture. These were significantly normalized postoperatively in cross section.

Horizontal Rectus Muscle Anatomy in Naturally and Artificially Strabismic Monkeys

Structural abnormalities of extraocular muscles (EOMs) or their pulleys are associated with some forms of human strabismus. This experiment was conducted to investigate whether such abnormalities are associated with artificial or naturally occurring strabismus in monkeys. Binocular alignment and grating visual acuities were determined in 10 monkeys representing various species using search coil recording and direct observations. Four animals were orthotropic, two had naturally occurring "A"-pattern esotropia, two had concomitant and one had "V"-pattern esotropia artificially induced by alternating or unilateral occlusion in infancy, and one had "A"-pattern exotropia artificially induced by prism wear. After euthanasia, 16 orbits were examined by high-resolution magnetic resonance imaging (MRI) in the quasi-coronal plane. Paths and sizes of horizontal rectus EOMs were analyzed quantitatively in a standardized coordinate system. Whole orbits were then serially sectioned en bloc in the quasi-coronal plane, stained for connective tissue, and compared with MRI. Nerve and EOM features were analyzed quantitatively. Quantitative analysis of MRI revealed no significant differences in horizontal rectus EOM sizes or paths among orthotropic or naturally or artificially strabismic monkeys. Histologic examination demonstrated no differences in EOM size, structure, or innervation among the three groups, and no differences in connective tissues in the pulley system. The accessory lateral rectus (ALR) EOM was present in all specimens, but was small, inconsistently located, and sparsely innervated. Characteristics of the ALR did not correlate with strabismus. Major structural abnormalities of horizontal rectus EOMs and associated pulleys are unrelated to natural or artificial horizontal strabismus in the monkeys studied. The ALR is unlikely to contribute to horizontal strabismus in primates. However, these findings do not exclude a possible role of pulley abnormalities in disorders such as cyclovertical strabismus.

Lymphocytic Infiltration and Enlargement of the Lacrimal Glands: A New Subtype of Primary Sjögren’s Syndrome?

<h3>Purpose</h3> To review the clinical, radiologic, serologic, histopathologic, immunohistochemical, and molecular genetic features of patients having Sjögren's syndrome (SS) with lacrimal gland enlargement. <h3>Design</h3> Retrospective case series review. <h3>Participants</h3> Fourteen patients histopathologically diagnosed with SS with lacrimal enlargement. Twenty-three age- and gender-matched controls were used for comparison on radiologic analysis. <h3>Methods</h3> Clinical and serologic data were determined directly or by chart review. Computed tomography images from patients were compared with those from the control group. Histopathologic sections were reviewed and graded using the Chisholm-Mason scale, and quantitative immunohistochemical analysis was applied. <h3>Main Outcome Measures</h3> Clinically, patients were assessed for age, gender, onset, symptoms and signs, systemic features, treatment, and outcome. Existing histologic specimens were reviewed according to the Chisholm-Mason scale, and then the percentages of plasma cells containing immunoglobulin (Ig) A, IgG, and IgM were determined. Imaging was assessed for lacrimal gland thickness, prolapse, density, and margin contour; extraocular muscle size; orbital tissue displacement; and proptosis. <h3>Results</h3> Clinical and histopathological data fulfilled the revised American-European criteria for primary SS in 79% of patients. Compared with other large series of primary SS patients, similarities were found with age, xerophthalmia, parotidomegaly, and articular involvement. Differences included a lower incidence of autoantibodies, xerostomia, and extraglandular features and a higher male-to-female ratio. In almost all patients (93%), the percentage of plasma cells positive for IgA was less than 70%, consistent with SS. Compared with controls, the lacrimal glands were enlarged significantly (<i>P</i><0.0001) and prolapsed (<i>P</i><0.001). Involved glands had blurred margins (<i>P</i><0.007), caused displacement of adjacent tissues (<i>P</i> = 0.03), and were associated with hyperdense fat (<i>P</i> = 0.007). Lymphocytic infiltration of orbital fat was present in all patients for whom fat biopsy results were available. Three patients had monoclonal infiltrates, and 1 patient experienced subsequent extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue type, 4 years after presentation. <h3>Conclusions</h3> The criteria used to diagnose primary SS are controversial, but both diagnostic and quantitative immunohistochemical criteria suggest that these patients, with lacrimal gland enlargement resulting from lymphocytic infiltration, represent a new subtype of primary SS. This is clinically important in view of the increased risk of lymphoma associated with SS, compared with idiopathic nonspecific lacrimal inflammation.

Severe strabismus after scleral buckling: Multiple mechanisms revealed by high-resolution magnetic resonance imaging

Strabismus occurring after scleral buckling for retinal detachment typically is attributed to scarring, but this is not the only mechanism. We investigated use of magnetic resonance imaging (MRI) to identify a spectrum of mechanisms of strabismus occurring after scleral buckling. Prospective, noncomparative, observational case series in an academic referral setting. Six patients with long-standing, large-angle strabismus after monocular or binocular scleral buckling. Horizontal and vertical preoperative deviations, present from 8 to 120 months, ranged from 25 prism diopters to more than 90 prism diopters. Multipositional high-resolution MRI of both orbits was performed using surface coils in multiple, controlled gaze positions. Coronal, sagittal, and axial images were obtained as clinically appropriate. Different mechanisms of pathologic characteristics of the extraocular muscles (EOMs) in complicated strabismus after scleral buckling. Magnetic resonance imaging readily demonstrated EOM size and contractility, as well as features of scleral buckle hardware such as grooves and junctions and relationships of EOMs to the buckle and sclera. Imaging demonstrated that 5 rectus EOMs were disinserted from the globe at the buckle: 2 superior rectus, 2 medial rectus, and 1 lateral rectus. One patient with suspected inferior rectus muscle disinsertion had restrictive strabismus as a result of interference by a meridional explant and myopic staphyloma. Magnetic resonance imaging demonstrated anterior migration and transection by the silicone element through rectus EOMs in 3 patients. Disinserted EOMs were retrieved successfully by transconjunctival surgery in 4 patients and by orbitotomy in 1 patient, markedly improving alignment even as long as 5 years after EOM disinsertion. Multipositional high-resolution MRI provides valuable information such as location and contractile potential of disinserted EOMs, as well as mass effect from the scleral buckle. Preoperative orbital MRI may be a useful tool to distinguish multiple mechanisms of persistent severe strabismus after scleral buckling and is helpful in surgical planning.

A new MRI method for the quantitative evaluation of extraocular muscle size in thyroid ophthalmopathy.

In cross section, extraocular muscles are more or less elliptical, with short and long diameters. We studied the ratio (R) of short to long diameter and investigated its use in quantitative assessment of the extraocular muscles in patients with Graves's disease. We measured the diameters on T1-weighted axial and coronal MRI and computed R for each extraocular muscle in 80 patients without and 40 with Graves's disease. We compared the measurements and R of the right and left orbits, and of men and women. The short diameter of all extraocular muscles apart from the superior oblique showed significant differences between men and women, and that of the inferior rectus varied significantly with age. R, however, was unrelated to sex or age. All patients with Graves's disease and an increased short diameter also had an increased R, but 6% of the muscles showed an increase in R, even though their short diameter was within the normal range.

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. (J AAPOS 2002;6:337-47)

Quantitative CT of the orbit in Graves' disease.

In order to determine the value of quantitative CT of the orbit in patients with Graves' disease, we clinically examined 174 orbits of 87 patients with Graves' disease and evaluated them by CT in respect to the density and size of the extraocular muscles, the globe position and the width of the optic nerve-sheath complex. We also determined the normal ranges for density of extraocular muscles in 200 normal orbits of 100 patients for comparison. Normal ranges for the density of extraocular muscles were (mean +/- 2 SD) medial rectus, 28-63 HU; lateral rectus, 24-78 HU; inferior rectus, 20-64 HU; superior muscle group, 28-62 HU. 51 of 77 (66%) patients with Graves' disease had extraocular muscle density changes. Some extraocular muscles showed fatty infiltration on CT. 50 of 87 (57%) patients had at least one enlarged extraocular muscle, 47 (54%) patients had exophthalmos and 59 (68%) patients had either exophthalmos and/or extraocular muscle enlargement. A diagnosis of Graves' ophthalmopathy was made in 69 of 87 (79%) patients using CT and in 50 (57%) patients by clinical examination. We conclude that quantitative CT imaging of the orbit with evaluation of the size and density values of extraocular muscles and the globe position may be very helpful in detecting ophthalmopathy in patients with Graves' disease.

Extraocular Muscle Size Comparison between Normal and Myopic Eyes Using Standardized A Scan Echography

The aim of this study was to establish the range of diameters of extraocular muscles in myopic patients and to obtain the baseline data to follow progression or regression of pathologies involving them. Standardized A scan and B scan ultrasound was used to measure the thickness of straight extraocular muscles at the muscle belly. No statistical differences were seen between right and left eyes. We found no consistent correlation with age or with axial length in the control or in the myopic patients (p>0.05). Diameters in myopic and control eyes were similar. This lack of difference between myopic and control muscle sizes means that we can obtain accurate measurements also from myopic patients.