The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Joseph L Demer - One of the best experts on this subject based on the ideXlab platform.
-
the effect of axial length on Extraocular Muscle leverage
American Journal of Ophthalmology, 2020Co-Authors: Robert A Clark, Joseph L DemerAbstract:Purpose Magnetic resonance imaging was used to determine the effect of axial length (AL) on globe rotational axis and horizontal Extraocular Muscle leverage during horizontal duction. Design Prospective observational case series. Methods At a single academic center, 36 orthophoric adults with a wide range of ALs underwent high-resolution axial orbital magnetic resonance imaging in target-controlled adduction and abduction. ALs were measured in planes containing maximum globe cross-sections. Area centroids were calculated to determine globe centers. Rotational axes in orbital coordinates were calculated from displacements of lens centers and globe–optic nerve attachments. Lever arms were calculated as distances between published Extraocular Muscle insertions and rotational axes. Results ALs averaged 26.3 ± 0.3 mm (standard error [range 21.5-33.4 mm]). Rotational axes from adduction to abduction averaged 1.1 ± 0.2 mm medial and 1.1 ± 0.2 mm anterior to the globe's geometric center in adduction. Linear regression demonstrated no significant correlation between AL and rotational axis horizontal (R2 = 0.06) or anteroposterior (R2 = 0.07) position. Medial rectus (MR) lever arms averaged 12.0 ± 0.2 mm and lateral rectus (LR) lever arms averaged 12.8 ± 0.2 mm. Both MR (R2 = 0.24, P Conclusions Regardless of AL, the globe rotates about a point nasal and anterior to its geometric center, giving the LR more leverage than the MR. This eccentricity may diminish the effect of tendon repositioning in moderate to highly myopic patients, with reductions in per-mill imeter dose/response predicted with longer AL.
-
Extraocular Muscle compartments in superior oblique palsy
Investigative Ophthalmology & Visual Science, 2016Co-Authors: Soh Youn Suh, Robert A Clark, Joseph L DemerAbstract:Purpose To investigate changes in volumes of Extraocular Muscle (EOM) compartments in unilateral superior oblique (SO) palsy using magnetic resonance imaging (MRI). Methods High-resolution, surface-coil MRI was obtained in 19 patients with unilateral SO palsy and 19 age-matched orthotropic control subjects. Rectus EOMs and the SO were divided into two anatomic compartments for volume analysis in patients with unilateral SO palsy, allowing comparison of total compartmental volumes versus controls. Medial and lateral compartmental volumes of the SO Muscle were compared in patients with isotropic (round shape) versus anisotropic (elongated shape) SO atrophy. Results The medial and lateral compartments of the ipsilesional SO Muscles were equally atrophic in isotropic SO palsy, whereas the lateral compartment was significantly smaller than the medial in anisotropic SO palsy (P = 0.01). In contrast to the SO, there were no differential compartmental volume changes in rectus EOMs; however, there was significant total Muscle hypertrophy in the ipsilesional inferior rectus (IR) and lateral rectus (LR) Muscles and contralesional superior rectus (SR) Muscles. Medial rectus (MR) volume was normal both ipsi- and contralesionally. Conclusions A subset of patients with SO palsy exhibit selective atrophy of the lateral, predominantly vertically acting SO compartment. Superior oblique atrophy is associated with whole-Muscle volume changes in the ipsilesional IR, ipsilesional LR, and contralesional SR; however, SO Muscle atrophy is not associated with compartmentally selective volume changes in the rectus EOMs. Selective compartmental SO pathology may provide an anatomic mechanism that explains some of the variability in clinical presentations of SO palsy.
-
changes in Extraocular Muscle volume during ocular duction
Investigative Ophthalmology & Visual Science, 2016Co-Authors: Robert A Clark, Joseph L DemerAbstract:PURPOSE It has been tacitly assumed that overall Extraocular Muscle (EOM) volume is conserved during contraction and relaxation, yet this assumption has been untested up to now. We used high-resolution magnetic resonance imaging (MRI) to determine if total EOM volume changes during relaxation and contraction. METHODS Surface coil MRI in quasi-coronal planes was obtained in target-controlled, maximal secondary gaze positions in 30 orbits of 15 normal subjects at 312-μm resolution. Ductions were quantified by changes in globe-optic nerve positions. Cross-sections of EOM were manually outlined in contiguous image planes so that volumes could be calculated by multiplying summed cross sections by the 2-mm slice thickness. Three-dimensional reconstruction allowed measurement of the lengths of terminal, unresolvable EOM segments, providing estimates of terminal EOM volumes to be summed with measured midorbital volumes to obtain total EOM volumes. RESULTS Duction range averaged 44.3 ± 4.8° from relaxation to contraction. There was a significant increase in total volume in each rectus EOM from relaxation to contraction: superior rectus (SR) 92 ± 36 mm3 (+18%, P < 10-11); inferior rectus (IR) 51 ± 18 mm3 (+9%, P < 10-11); medial rectus (MR) 78 ± 36 mm3 (+11%, P < 10-5); and lateral rectus (LR) 47 ± 45 mm3 (+7%, P = 0.005). Because volume changes for SR and MR exceed IR and LR, total rectus EOM volume increases in supraduction 41 ± 42 mm3 (+3.7%) and adduction 32 ± 63 mm3 (+2.3%). CONCLUSIONS Total EOM volume is not conserved but instead increases with contraction and decreased with relaxation. Contractile volume increases may be secondary to increased actin-myosin lattice spacing, so that density decreases. This effect is opposite that of possible hemodynamic changes.
-
superior oblique Extraocular Muscle shape in superior oblique palsy
American Journal of Ophthalmology, 2015Co-Authors: Sun Young Shin, Joseph L DemerAbstract:Purpose To investigate the superior oblique (SO) Extraocular Muscle cross section in normal controls and in SO palsy using high-resolution magnetic resonance imaging (MRI). Design Prospective observational study. Methods At a single academic medical center, high-resolution MRI was obtained at 312 μm in-plane resolution using surface coils in multiple, contiguous, quasi-coronal planes perpendicular to the orbital axis in 12 controls and 62 subjects with SO palsy. Previous strabismus surgery was excluded. Imaging was repeated in central gaze and infraduction. In each image plane along the SO, its cross section was outlined to compute cross-sectional area and the major and minor axes of the best-fitting ellipse. Main outcome measures were SO morphology and ocular motility. Results The major and minor axes, cross-sectional area distributions, and volume of the SO belly were subnormal in orbits with SO palsy at most anteroposterior locations ( P = .001), but discriminant analysis showed that palsied SO cross sections segregated distinctly into round and elongate shapes representing isotropic vs anisotropic atrophy, respectively. The major axis was relatively preserved in anisotropic atrophy ( P = .0146). Cases with isotropic atrophy exhibited greater hypertropia in infraversion than central gaze, as well as greater excyclotorsion, than cases with anisotropic atrophy ( P Conclusions Characteristic differences in shape of the palsied SO belly correlate with different clinical features, and may reflect both the degree of differential pathology in the medial vs lateral neuromuscular SO compartments and the basis for diversity in patterns of resulting hypertropia.
-
independent active contraction of Extraocular Muscle compartments
Investigative Ophthalmology & Visual Science, 2015Co-Authors: Andrew Shin, Lawrence Yoo, Joseph L DemerAbstract:Purpose. Intramuscular innervation of horizontal rectus Extraocular Muscle (EOMs) is segregated into superior and inferior (transverse) compartments, whereas all EOMs are also divided into global (GL) and orbital (OL) layers with scleral and pulley insertions, respectively. Mechanical independence between both types of compartments has been demonstrated during passive tensile loading. We examined coupling between EOM compartments during active, ex vivo contraction.
John D Porter - One of the best experts on this subject based on the ideXlab platform.
-
constitutive properties not molecular adaptations mediate Extraocular Muscle sparing in dystrophic mdx mice
The FASEB Journal, 2003Co-Authors: John D Porter, Anita P. Merriam, Francisco H. Andrade, Georgiana Cheng, Sangeeta Khanna, Chelliah R Richmonds, Patrick Leahy, Paraskevi Karathanasis, Xiaohua Zhou, Linda L KusnerAbstract:SPECIFIC AIMSOur aim was to test mechanisms potentially responsible for protection of the Extraocular Muscles in an animal model of Duchenne muscular dystrophy.PRINCIPAL FINDINGSUsing the mdx mouse, we systematically tested putative mechanisms that could protect Extraocular Muscle from the cyclic degeneration and regeneration characteristic of dystrophin-based muscular dystrophy. Putative Muscle-sparing mechanisms were predicted from existing models of the pathogenesis of muscular dystrophy, including functional replacement of dystrophin by utrophin, maintained calcium homeostasis in the face of sarcolemmal defects, preservation of nitric oxide (NO) myofiber-to-vasculature signaling, and compensation by an α7β1 integrin to laminin-α2 linkage that parallels the dystrophin-glycoprotein complex (DGC). We used high density oligonucleotide microarrays to uncover any other unanticipated mechanisms that may contribute to the absence of pathology in eye Muscle.1. Dystrophin-deficient Extraocular Muscles expresses...
-
Paradoxical absence of M lines and downregulation of creatine kinase in mouse Extraocular Muscle
Journal of applied physiology (Bethesda Md. : 1985), 2003Co-Authors: Francisco H. Andrade, Katrin Hayess, Anita P. Merriam, Georgiana Cheng, Wei Guo, Colleen A. Mcmullen, Peter F.m. Van Der Ven, John D PorterAbstract:The M lines are structural landmarks in striated Muscles, necessary for sarcomeric stability and as anchoring sites for the M isoform of creatine kinase (CK-M). These structures, especially prominent in fast skeletal Muscles, are missing in rodent Extraocular Muscle, a particularly fast and active Muscle group. In this study, we tested the hypotheses that 1). myomesin and M protein (cytoskeletal components of the M lines) and CK-M are downregulated in mouse Extraocular Muscle compared with the leg Muscles, gastrocnemius and soleus; and 2). the expression of other cytosolic and mitochondrial CK isoforms is correspondingly increased. As expected, mouse Extraocular Muscles expressed lower levels of myomesin, M protein, and CK-M mRNA than the leg Muscles. Immunocytochemically, myomesin and M protein were not detected in the banding pattern typically seen in other skeletal Muscles. Surprisingly, message abundance for the other known CK isoforms was also lower in the Extraocular Muscles. Moreover, total CK activity was significantly decreased compared with that in the leg Muscles. Based on these data, we reject our second hypothesis and propose that other energy-buffering systems may be more important in the Extraocular Muscles. The downregulation of major structural and metabolic elements and relative overexpression of two adenylate kinase isoforms suggest that the Extraocular Muscle group copes with its functional requirements by using strategies not seen in typical skeletal Muscles.
-
Extraocular Muscle: cellular adaptations for a diverse functional repertoire.
Annals of the New York Academy of Sciences, 2002Co-Authors: John D PorterAbstract:: Oculomotor control systems are considerably more complex and diverse than are spinal skeletomotor systems. Moreover, individual skeletal Muscles are frequently functional role-specific, while all Extraocular Muscles operate across a very wide dynamic range. We contend that the novel phenotype of the Extraocular Muscles is a direct consequence of the functional demands imposed upon this Muscle group by the central eye movement controllers. This review highlights five basic themes of Extraocular Muscle biology that set them apart from more typical skeletal Muscles, specifically, the (a) novel innervation pattern, (b) heterogeneity in contractile proteins, (c) structural and functional compartmentalization of the rectus and oblique Muscles, (d) diversity of Extraocular Muscle fiber types, and (e) relationship between the novel Muscle phenotype and the differential response of these Muscles in neuromuscular and endocrine disease. Finally, new data from broad genome-wide profiling studies are reviewed, with global gene expression patterns lending substantial support to the notion that the Extraocular Muscles are fundamentally different from traditional skeletal Muscle. This novel eye Muscle phenotype represents an adaptation that exploits the full range of variability in skeletal Muscle to meet the needs of visuomotor systems.
-
Extraocular Muscle is defined by a fundamentally distinct gene expression profile
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: John D Porter, Anita P. Merriam, Henry J. Kaminski, Sangeeta Khanna, Jonnagadda S Rao, Chelliah R Richmonds, Patrick Leahy, Francisco H. AndradeAbstract:Skeletal Muscle fibers are defined by patterned covariation of key traits that determine contractile and metabolic characteristics. Although the functional properties of most skeletal Muscles result from their proportional content of a few conserved Muscle fiber types, some, typically craniofacial, Muscles exhibit fiber types that appear to lie outside the common phenotypic range. We analyzed gene expression profiles of three putative Muscle classes, limb, masticatory, and Extraocular Muscle (EOM), in adult mice by high-density oligonucleotide arrays. Pairwise comparisons using conservative acceptance criteria identified expression differences in 287 genes between EOM and limb and/or masticatory Muscles. Use of significance analysis of microarrays methodology identified up to 400 genes as having an EOM-specific expression pattern. Genes differentially expressed in EOM reflect key aspects of Muscle biology, including transcriptional regulation, sarcomeric organization, excitation-contraction coupling, intermediary metabolism, and immune response. These patterned differences in gene expression define EOM as a distinct Muscle class and may explain the unique response of these Muscles in neuromuscular diseases.
-
the sparing of Extraocular Muscle in dystrophinopathy is lost in mice lacking utrophin and dystrophin
Journal of Cell Science, 1998Co-Authors: John D Porter, Jill A Rafael, R J Ragusa, J K Brueckner, J I Trickett, Kay E DaviesAbstract:The Extraocular Muscles are one of few skeletal Muscles that are structurally and functionally intact in Duchenne muscular dystrophy. Little is known about the mechanisms responsible for differential sparing or targeting of Muscle groups in neuromuscular disease. One hypothesis is that constitutive or adaptive properties of the unique Extraocular Muscle phenotype may underlie their protection in dystrophinopathy. We assessed the status of Extraocular Muscles in the mdx mouse model of muscular dystrophy. Mice showed mild pathology in accessory Extraocular Muscles, but no signs of pathology were evident in the principal Extraocular Muscles at any age. By immunoblotting, the Extraocular Muscles of mdx mice exhibited increased levels of a dystrophin analog, dystrophin-related protein or utrophin. These data suggest, but do not provide mechanistic evidence, that utrophin mediates eye Muscle protection. To examine a potential causal relationship, knockout mouse models were used to determine whether eye Muscle sparing could be reversed. Mice lacking expression of utrophin alone, like the dystrophin-deficient mdx mouse, showed no pathological alterations in Extraocular Muscle. However, mice deficient in both utrophin and dystrophin exhibited severe changes in both the accessory and principal Extraocular Muscles, with the eye Muscles affected more adversely than other skeletal Muscles. Selected Extraocular Muscle fiber types still remained spared, suggesting the operation of an alternative mechanism for Muscle sparing in these fiber types. We propose that an endogenous upregulation of utrophin is mechanistic in protecting Extraocular Muscle in dystrophinopathy. Moreover, data lend support to the hypothesis that interventions designed to increase utrophin levels may ameliorate the pathology in other skeletal Muscles in Duchenne muscular dystrophy.
Steven E Feldon - One of the best experts on this subject based on the ideXlab platform.
-
correction of restricted Extraocular Muscle motility in surgical management of strabismus in graves ophthalmopathy
Ophthalmology, 2002Co-Authors: Vu Nguyen, Dong Jun John Park, Lori Levin, Steven E FeldonAbstract:Abstract Objective To compare the success rates for strabismus surgery designed to correct limitation of duction with surgery designed to correct deviation in patients with Graves' ophthalmopathy. Design Retrospective nonrandomized comparative trial. Participants One hundred thirty-seven patients with Graves' ophthalmopathy who had undergone at least one Extraocular Muscle surgery were divided into two groups: those whose first surgery occurred before June 1997 (control group) and those whose first surgery occurred in June 1997 or thereafter (case group). Interventions Extraocular Muscle surgery primarily directed at either correcting deviation (control group) or correcting limitation of ductions (case group). Main outcome measures Postoperative deviations in the primary position were measured in prism diopters 30 to 180 days after surgery. A postoperative deviation of less than 5 diopters was considered a successful surgical outcome. Results Patients undergoing strabismus surgery specifically designed to correct limitation of duction achieved a 74% success rate compared with a 44% success rate in the control group (P Conclusions Compared with surgery aimed primarily at the correction of deviation, Extraocular Muscle surgery tailored to address restriction of ductions in patients with Graves' ophthalmopathy is associated with improved surgical success of initial realignment and with a lower rate of reoperation
-
graves exophthalmos unrelated to Extraocular Muscle enlargement superior rectus Muscle inflammation may induce venous obstruction
Ophthalmology, 1991Co-Authors: Henry L Hudson, Lori Levin, Steven E FeldonAbstract:Exophthalmos is the most commonly measured sign of Graves ophthalmopathy, whereas enlargement of the Extraocular Muscles is the principal pathologic abnormality. The purpose of this article is to explore possible etiologies of increased volume of orbital fat and of proptosis in patients with no substantially increased total Extraocular Muscle volume. Computed tomographic scans of the 13 orbits reviewed in this study had the following characteristics in common: a fine, reticular pattern within the orbital fat, a prominent superior ophthalmic vein, and an enlarged superior rectus Muscle. Quantitative analysis revealed that superior rectus Muscle volume showed a statistically significant correlation with proptosis, whereas medial, lateral, and inferior rectus Muscle volumes did not correlate with proptosis. Based on anatomic considerations, the authors postulate that superior rectus Muscle enlargement alone may produce reduced venous outflow from the orbit, thereby expanding the apparent orbital fat volume and producing proptosis.
Robert A Clark - One of the best experts on this subject based on the ideXlab platform.
-
the effect of axial length on Extraocular Muscle leverage
American Journal of Ophthalmology, 2020Co-Authors: Robert A Clark, Joseph L DemerAbstract:Purpose Magnetic resonance imaging was used to determine the effect of axial length (AL) on globe rotational axis and horizontal Extraocular Muscle leverage during horizontal duction. Design Prospective observational case series. Methods At a single academic center, 36 orthophoric adults with a wide range of ALs underwent high-resolution axial orbital magnetic resonance imaging in target-controlled adduction and abduction. ALs were measured in planes containing maximum globe cross-sections. Area centroids were calculated to determine globe centers. Rotational axes in orbital coordinates were calculated from displacements of lens centers and globe–optic nerve attachments. Lever arms were calculated as distances between published Extraocular Muscle insertions and rotational axes. Results ALs averaged 26.3 ± 0.3 mm (standard error [range 21.5-33.4 mm]). Rotational axes from adduction to abduction averaged 1.1 ± 0.2 mm medial and 1.1 ± 0.2 mm anterior to the globe's geometric center in adduction. Linear regression demonstrated no significant correlation between AL and rotational axis horizontal (R2 = 0.06) or anteroposterior (R2 = 0.07) position. Medial rectus (MR) lever arms averaged 12.0 ± 0.2 mm and lateral rectus (LR) lever arms averaged 12.8 ± 0.2 mm. Both MR (R2 = 0.24, P Conclusions Regardless of AL, the globe rotates about a point nasal and anterior to its geometric center, giving the LR more leverage than the MR. This eccentricity may diminish the effect of tendon repositioning in moderate to highly myopic patients, with reductions in per-mill imeter dose/response predicted with longer AL.
-
Extraocular Muscle compartments in superior oblique palsy
Investigative Ophthalmology & Visual Science, 2016Co-Authors: Soh Youn Suh, Robert A Clark, Joseph L DemerAbstract:Purpose To investigate changes in volumes of Extraocular Muscle (EOM) compartments in unilateral superior oblique (SO) palsy using magnetic resonance imaging (MRI). Methods High-resolution, surface-coil MRI was obtained in 19 patients with unilateral SO palsy and 19 age-matched orthotropic control subjects. Rectus EOMs and the SO were divided into two anatomic compartments for volume analysis in patients with unilateral SO palsy, allowing comparison of total compartmental volumes versus controls. Medial and lateral compartmental volumes of the SO Muscle were compared in patients with isotropic (round shape) versus anisotropic (elongated shape) SO atrophy. Results The medial and lateral compartments of the ipsilesional SO Muscles were equally atrophic in isotropic SO palsy, whereas the lateral compartment was significantly smaller than the medial in anisotropic SO palsy (P = 0.01). In contrast to the SO, there were no differential compartmental volume changes in rectus EOMs; however, there was significant total Muscle hypertrophy in the ipsilesional inferior rectus (IR) and lateral rectus (LR) Muscles and contralesional superior rectus (SR) Muscles. Medial rectus (MR) volume was normal both ipsi- and contralesionally. Conclusions A subset of patients with SO palsy exhibit selective atrophy of the lateral, predominantly vertically acting SO compartment. Superior oblique atrophy is associated with whole-Muscle volume changes in the ipsilesional IR, ipsilesional LR, and contralesional SR; however, SO Muscle atrophy is not associated with compartmentally selective volume changes in the rectus EOMs. Selective compartmental SO pathology may provide an anatomic mechanism that explains some of the variability in clinical presentations of SO palsy.
-
changes in Extraocular Muscle volume during ocular duction
Investigative Ophthalmology & Visual Science, 2016Co-Authors: Robert A Clark, Joseph L DemerAbstract:PURPOSE It has been tacitly assumed that overall Extraocular Muscle (EOM) volume is conserved during contraction and relaxation, yet this assumption has been untested up to now. We used high-resolution magnetic resonance imaging (MRI) to determine if total EOM volume changes during relaxation and contraction. METHODS Surface coil MRI in quasi-coronal planes was obtained in target-controlled, maximal secondary gaze positions in 30 orbits of 15 normal subjects at 312-μm resolution. Ductions were quantified by changes in globe-optic nerve positions. Cross-sections of EOM were manually outlined in contiguous image planes so that volumes could be calculated by multiplying summed cross sections by the 2-mm slice thickness. Three-dimensional reconstruction allowed measurement of the lengths of terminal, unresolvable EOM segments, providing estimates of terminal EOM volumes to be summed with measured midorbital volumes to obtain total EOM volumes. RESULTS Duction range averaged 44.3 ± 4.8° from relaxation to contraction. There was a significant increase in total volume in each rectus EOM from relaxation to contraction: superior rectus (SR) 92 ± 36 mm3 (+18%, P < 10-11); inferior rectus (IR) 51 ± 18 mm3 (+9%, P < 10-11); medial rectus (MR) 78 ± 36 mm3 (+11%, P < 10-5); and lateral rectus (LR) 47 ± 45 mm3 (+7%, P = 0.005). Because volume changes for SR and MR exceed IR and LR, total rectus EOM volume increases in supraduction 41 ± 42 mm3 (+3.7%) and adduction 32 ± 63 mm3 (+2.3%). CONCLUSIONS Total EOM volume is not conserved but instead increases with contraction and decreased with relaxation. Contractile volume increases may be secondary to increased actin-myosin lattice spacing, so that density decreases. This effect is opposite that of possible hemodynamic changes.
Sun Young Shin - One of the best experts on this subject based on the ideXlab platform.
-
Effects of the Rho-Kinase Inhibitor Y-27632 on Extraocular Muscle Surgery in Rabbits.
Journal of ophthalmology, 2017Co-Authors: Ji-sun Moon, Hyun-kyung Kim, Sun Young ShinAbstract:To evaluate the effect of the Rho-kinase inhibitor Y-27632 on postoperative inflammation and adhesion following Extraocular Muscle surgery in rabbits. The superior rectus Muscle reinsertion was performed on both eyes of 8 New Zealand white rabbits. After reinsertion, the rabbits received subconjunctival injections of the Rho-kinase inhibitor and saline on each eye. To assess acute and late inflammatory changes, Ki-67, CD11β+, and F4/80 were evaluated and the sites of Muscle reattachment were evaluated for a postoperative adhesion score and histopathologically for collagen formation. F4/80 antibody expression was significantly different in the Rho-kinase inhibitor-injected group at both postoperative day 3 and week 4 (p = 0.038, 0.031). However, Ki-67 and CD11β+ were not different the between two groups. The difference in the SRM/conjunctiva adhesion score between the two groups was also significant (p = 0.034). Conclusion. Intraoperative subconjunctival injection of the Rho-kinase inhibitor may be effective for adjunctive management of inflammation and fibrosis in rabbit eyes following Extraocular Muscle surgery.
-
superior oblique Extraocular Muscle shape in superior oblique palsy
American Journal of Ophthalmology, 2015Co-Authors: Sun Young Shin, Joseph L DemerAbstract:Purpose To investigate the superior oblique (SO) Extraocular Muscle cross section in normal controls and in SO palsy using high-resolution magnetic resonance imaging (MRI). Design Prospective observational study. Methods At a single academic medical center, high-resolution MRI was obtained at 312 μm in-plane resolution using surface coils in multiple, contiguous, quasi-coronal planes perpendicular to the orbital axis in 12 controls and 62 subjects with SO palsy. Previous strabismus surgery was excluded. Imaging was repeated in central gaze and infraduction. In each image plane along the SO, its cross section was outlined to compute cross-sectional area and the major and minor axes of the best-fitting ellipse. Main outcome measures were SO morphology and ocular motility. Results The major and minor axes, cross-sectional area distributions, and volume of the SO belly were subnormal in orbits with SO palsy at most anteroposterior locations ( P = .001), but discriminant analysis showed that palsied SO cross sections segregated distinctly into round and elongate shapes representing isotropic vs anisotropic atrophy, respectively. The major axis was relatively preserved in anisotropic atrophy ( P = .0146). Cases with isotropic atrophy exhibited greater hypertropia in infraversion than central gaze, as well as greater excyclotorsion, than cases with anisotropic atrophy ( P Conclusions Characteristic differences in shape of the palsied SO belly correlate with different clinical features, and may reflect both the degree of differential pathology in the medial vs lateral neuromuscular SO compartments and the basis for diversity in patterns of resulting hypertropia.
