Extraocular Muscle Size Research Articles

Comparison of Standardized Echography with Magnetic Resonance Imaging to Measure Extraocular Muscle Size

Comparison of Standardized Echography with Magnetic Resonance Imaging to Measure Extraocular Muscle Size

Comparison of Standardized Echography with Magnetic Resonance Imaging to Measure Extraocular Muscle Size

Using both standardized echography and high-resolution, surface coil magnetic resonance imaging, we measured the transverse diameter of recti extraocular muscles to evaluate comparative accuracy. Maximum transverse diameter of each rectus muscle in primary gaze was measured in 39 orbits of 20 subjects by using standardized A-scan echography. In the same orbits, we obtained multiple coronal magnetic resonance imaging planes by using a surface coil to span the anteroposterior extent of each orbit. Digital image analysis with the National Institutes of Health Image program was used to measure transverse muscle diameter. Average size for each rectus muscle was similar for the echographic and magnetic resonance imaging techniques. However, linear regressions of individual ultrasound against magnetic resonance imaging measurements showed coefficients of determination (R 2 ) moderate (0.29) for inferior recti muscles and low (≤0.11) for other recti muscles. For most recti muscles, significant variability in echographic estimates of muscle width results from factors other than true muscle size. Results indicate that ultrasound measurements of muscle size in individual patients should be interpreted cautiously.

Comparison of Standardized Echography With Magnetic Resonance Imaging to Measure Extraocular Muscle Size

Using both standardized echography and high-resolution, surface coil magnetic resonance imaging, we measured the transverse diameter of recti extraocular muscles to evaluate comparative accuracy. Maximum transverse diameter of each rectus muscle in primary gaze was measured in 39 orbits of 20 subjects by using standardized A-scan echography. In the same orbits, we obtained multiple coronal magnetic resonance imaging planes by using a surface coil to span the anteroposterior extent of each orbit. Digital image analysis with the National Institutes of Health Image program was used to measure transverse muscle diameter. Average size for each rectus muscle was similar for the echographic and magnetic resonance imaging techniques. However, linear regressions of individual ultrasound against magnetic resonance imaging measurements showed coefficients of determination (R2) moderate (0.29) for inferior recti muscles and low (< or = 0.11) for other recti muscles. For most recti muscles, significant variability in echographic estimates of muscle width results from factors other than true muscle size. Results indicate that ultrasound measurements of muscle size in individual patients should be interpreted cautiously.

Extraocular Muscle Size Comparison Using Standardized A-scan Echography and Computerized Tomography Scan Measurements

In many clinical situations, the standard for evaluating extraocular muscle (EOM) size, particularly in thyroid ophthalmopathy, has been use of the computerized tomography (CT) scanner. The impression is generally reported as “enlarged or normal EOMs.” If the report of “normal EOM” on CT scan weighs heavily against the diagnosis of thyroid eye disease, how does this qualitative assessment compare with the diagnostic modality of ultrasound? The technique of standardized A-scan measurement of extraocular muscles has been extremely accurate. In this paper, standardized A-scan measurements and CT scan estimates of EOMs are compared in a series of ten patients with a clinical diagnosis of Graves' disease. Three of ten patients displayed enlarged EOMs by CT interpretations; seven of ten patients were categorized as consistent with Graves' disease by correlation with current ultrasonographic criteria for muscle enlargement, asymmetry, and high irregularity of tissue reflectivity.

Elasmobranch oculomotor organization: Anatomical and theoretical aspects of the phylogenetic development of vestibulo‐oculomotor connectivity

The oculomotor organization of two elasmobranch species, smooth dogfish (Mustelus canis) and little skate (Raja erinacea), was studied by investigating the extraocular muscle apparatus and the oculomotor motoneuron distribution. The macroscopic appearance of the eye muscles was similar to any lateral-eyed vertebrate species (e.g., goldfish, rabbit). The size of extraocular muscles was expressed by counting single muscle fibers and comparing cross-sectional areas of the extraocular muscles. There were significant differences in the number of fibers in the six extraocular muscles in dogfish, but not in skate. Fiber sizes varied considerably; thus, the number of fibers did not relate to cross-sectional areas. In the dogfish, no one pair of agonist-antagonist extraocular muscles was larger than the others, suggesting that there was no preference for eye movements in a particular plane of space. However, the lateral rectus was more than twice the size of most of the other muscles. In the skate, cross-sectional areas of the horizontal eye muscles were smaller than those of the vertical eye movers. This may indicate a reduced utilization of horizontal eye muscles, which may reflect the bottom-dwelling habitat and mode of locomotion of the skate. The distribution of the extraocular motoneurons was determined by injecting horseradish peroxidase (HRP) into single eye muscles. Medial rectus, superior rectus, and superior oblique motoneuron populations were located contralateral to their respective muscles. Lateral rectus, inferior rectus, and inferior oblique motoneurons were located ipsilateral to their muscles. This distribution is in contrast to almost all other vertebrates studied thus far, where medial rectus motoneurons are located ipsilateral to the muscle which they innervate. The oculomotor arrangement in elasmobranchs is likely to have consequences for the circuitry responsible for the production of conjugate compensatory eye movements in the horizontal plane. We hypothesize that, in contrast to other vertebrates, the basic elasmobranch vestibulo-ocular reflex pathway consists of three identically structured three-neuron-arcs connecting the three semicircular canals to their respective extraocular muscles. This innervation pattern may constitute a special feature of the elasmobranch brain or a phylogenetically older arrangement of eye movement pathways.

GRAVES' DISEASE PRESENTING WITH BILATERAL ACUTE PAINFUL PROPTOSIS, PTOSIS, OPHTHALMOPLEGIA, AND VISUAL LOSS

Two middle-aged women presented with bilateral acute painful proptosis, ptosis, ophthalmoplegia, and visual loss. In both an initial diagnosis of orbital cellulitis was made, but they did not respond to systemic antibiotics. Orbital computerised tomographic (CT) scans were thus done within 36 h of admission and they showed grossly enlarged extraocular muscles in each case suggestive of dysthyroid eye disease. Clinical examination was otherwise normal. When high doses of systemic steroids were substituted for the antibiotics the physical signs resolved rapidly, accompanied by a dramatic reduction in the size of extraocular muscles on CT scanning. One patient subsequently became clinically hypothyroid, while the other showed clinical and biochemical evidence of thyroid overactivity. These case-reports suggest that patients with bilateral acute painful proptosis should have an early CT scan to exclude atypical dysthyroid disease. Delay in giving systemic steroids may allow the development of unnecessary visual loss due to optic nerve damage.