Eye Rotations, the Extraocular Muscles, and Strabismus Terminology

2008 ◽  
Author(s):  
Agnes Wong
Keyword(s):  
Skeletal Muscles ◽  
Muscle Fibers ◽  
Extraocular Muscles ◽  
The Body ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia ◽  
Eye Muscle ◽  
Roll Axis ◽  
Contraction And Relaxation ◽  
Duchenne's Dystrophy

To understand how eye muscles move the eyeball, it is necessary to understand the geometry of the eye and the functions of the muscles. The eyeball rotates about three axes: horizontal, vertical, and torsional. These axes intersect at the center of the eyeball. Eye rotations are achieved by coordinated contraction and relaxation of six extraocular muscles—four rectus and two oblique—attached to each eye. The action of the muscles on the globe is determined by the point of rotation of the globe, as well as the origin and insertion of each muscle. Recent evidence suggests that the muscles also exert their effects on the globe via the extraocular muscle pulleys. Considering that we make at least 100,000 saccades alone each day, it is not surprising that many extraocular muscles are very resistant to fatigue. Extraocular muscles are also different from other skeletal muscles in many respects. For example, eye muscle fibers are richly innervated, and each motoneuron innervates only 10–20 muscle fibers, the smallest motor unit known in the body. Extraocular muscles also have more mitochondria and a higher metabolic rate than other skeletal muscles. Thus, extraocular muscles are one of the fastest contracting muscles. This property allows animals to shift gaze swiftly, so that they can avoid approaching predators or detect prey in the vicinity. The unique immunologic and physiologic properties of extraocular muscles may also explain why they are more susceptible to certain disease processes, such as Grave’s disease and chronic progressive external ophthalmoplegia, but more resistant to others such as Duchenne’s dystrophy, which mainly affects skeletal muscles in the rest of the body. The eyeball rotates about three axes: x-axis (naso-occipital or roll axis), y-axis (earthhorizontal or pitch axis), and z-axis (earth-vertical or yaw axis). Ductions refer to monocular movements of each eye. They include abduction, adduction, elevation (sursumduction), depression (deorsumduction), incycloduction or incyclotorsion, and excycloduction or excyclotorsion (see table on opposite page). Versions refer to binocular conjugate movements of both eyes, such that the visual axes of the eyes move in the same direction. They include dextroversion, levoversion, elevation (sursumversion), depression (deorsumversion), dextrocycloversion, and levocycloversion (see table).

The mutations m.5628T>C and m.8348A>G in single muscle fibers of a patient with chronic progressive external ophthalmoplegia

2012 ◽  
Vol 320 (1-2) ◽  
pp. 131-135 ◽  
Author(s):  
Juliana Gamba ◽  
Beatriz Hitomi Kiyomoto ◽  
Acary Souza Bulle de Oliveira ◽  
Alberto Alain Gabbai ◽  
Beny Schmidt ◽  
...  
Keyword(s):  
Muscle Fibers ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia ◽  
Single Muscle

scholarly journals Understanding the extraocular muscles: connective tissue, motor endplates and the cytoskeleton

2020 ◽  
Vol 42 (5) ◽  
pp. 52-57
Author(s):  
Jing-Xia Liu ◽  
Nils Dennhag ◽  
Fatima Pedrosa Domellöf
Keyword(s):  
Visual Acuity ◽  
Connective Tissue ◽  
Coping Strategies ◽  
Skeletal Muscles ◽  
Premature Death ◽  
Extraocular Muscles ◽  
The Body ◽  
Motor Endplates ◽  
Severe Handicap ◽  
Future Treatment

We constantly direct our eyes to the object of interest with the help of the extraocular muscles, and thereby use foveal fixation to attain the best possible visual acuity. The muscles around the eye are rather different from other skeletal muscles, being, for example, simultaneously the fastest muscles in the body and impossible to exhaust. The most exciting property of the extraocular muscles is their unique response to disease, as they often remain unaffected in muscle conditions which lead to severe handicap and premature death. Understanding the coping strategies that allow the extraocular muscles to remain unaffected may provide clues for the future treatment of severe diseases such as muscle dystrophies.

The Extraocular Muscles

2012 ◽  
Author(s):  
David Jordan ◽  
Louise Mawn ◽  
Richard L. Anderson
Keyword(s):  
Skeletal Muscles ◽  
Dynamic Range ◽  
Striated Muscle ◽  
Muscle Fibers ◽  
Motor Units ◽  
Firing Frequency ◽  
Extraocular Muscles ◽  
Time To Peak ◽  
Coarse Fibers ◽  
Small Increments

Whereas skeletal muscles generally perform specific limited roles, extraocular muscles (EOMs) have to be responsive over a wider dynamic range. As a result, EOMs have fundamentally distinct structural, functional, biochemical, and immunological properties as compared to other skeletal muscles. At birth, the extraocular muscles are at approximately 50 % to 60 % of their final dimension. Their relative growth within the enlarging orbit and their angular relations with the globe remain nearly constant from infancy to adulthood. The adult rectus muscles are approximately the same length (40 mm) but differ in thickness and in the length of their tendons. There are six extrinsic, or extraocular, muscles of the eye: four recti and two obliques. Only the horizontal and vertical recti insert on the eyeball in front of its equator. Both obliques have their insertions behind the equator of the globe. All six muscles consist of striated muscle fibers with abundant elastic fibers. The EOMs have muscle fibers and innervations that differ from those of skeletal muscle. There are three distinct types of muscle fibers (fine, granular, and coarse) that contribute to the action of the EOMs. The fine fibers are thought to be responsible for slow twitch movements, the granular fibers for fast twitch movements, and the coarse fibers for slow tonic movements. The EOMs are more richly innervated than other voluntary muscles of the body and have three types of nerve terminals: single endplate (driving eye movements), multiple endplates (tonic tension), and palisade endings (can be sensory receptors). In addition, there are both singly and multiply innervated nerve fibers present. EOMs are able to vary their contractile force by small increments. The maximum firing frequency of ocular motor units is about four times greater than those of limb muscle motor units. To allow them to operate at a higher frequency, EOMs also have faster contractile properties, with their time to peak tension and their one-half relaxation time being at least half of those in limb muscles.

scholarly journals The functions of the proprioceptors of the eye muscles

2000 ◽  
Vol 355 (1404) ◽  
pp. 1685-1754 ◽  
Author(s):  
I.M.L. Donaldson
Keyword(s):  
Eye Movement ◽  
Visual Analysis ◽  
Extraocular Muscles ◽  
The Body ◽  
General Question ◽  
Eye Muscle ◽  
Eye Muscles ◽  
Visuomotor Behaviour ◽  
Extrapersonal Space ◽  
The Brain

This article sets out to present a fairly comprehensive review of our knowledge about the functions of the receptors that have been found in the extraocular muscles – the six muscles that move each eye of vertebrates in its orbit – of all the animals in which they have been sought, including Man. Since their discovery at the beginning of the 20th century these receptors have, at various times, been credited with important roles in the control of eye movement and the construction of extrapersonal space and have also been denied any function whatsoever. Experiments intended to study the actions of eye muscle receptors and, even more so, opinions (and indeed polemic) derived from these observations have been influenced by the changing fashions and beliefs about the more general question of how limb position and movement is detected by the brain and which signals contribute to those aspects of this that are p erceived (kinaesthesis). But the conclusions drawn from studies on the eye have also influenced beliefs about the mechanisms of kinaesthesis and, arguably, this influence has been even larger than that in the converse direction. Experimental evidence accumulated over rather more than a century is set out and discussed. It supports the view that, at the beginning of the 21st century, there are excellent grounds for believing that the receptors in the extraocular muscles are indeed proprioceptors, that is to say that the signals that they send into the brain are used to provide information about the position and movement of the eye in the orbit. It seems that this information is important in the control of eye movements of at least some types, and in the determination by the brain of the direction of gaze and the relationship of the organism to its environment. In addition, signals from these receptors in the eye muscles are seen to be necessary for the development of normal mechanisms of visual analysis in the mammalian visual cortex and for both the development and maintenance of normal visuomotor behaviour. Man is among those vertebrates to whose brains eye muscle proprioceptive signals provide information apparently used in normal sensorimotor functions; these include various aspects of perception, and of the control of eye movement. It is possible that abnormalities of the eye muscle proprioceptors and their signals may play a part in the genesis of some types of human squint (strabismus); conversely studies of patients with squint in the course of their surgical or pharmacological treatment have yielded much interesting evidence about the central actions of the proprioceptive signals from the extraocular muscles. The results of experiments on the eye have played a large part in the historical controversy, now in at least its third century, about the origin of signals that inform the brain about movement of parts of the body. Some of these results, and more of the interpretations of them, now need to be critically re–examined. The re–examination in the light of recent experiments that is presented here does not support many of the conclusions confidently drawn in the past and leads to both new insights and fresh questions about the roles of information from motor signals flowing out of the brain and that from signals from the peripheral receptors flowing into it. There remain many lacunae in our knowledge and filling some of these will, it is contended, be essential to advance our understanding further. It is argued that such understanding of eye muscle proprioception is a necessary part of the understanding of the physiology and pathophysiology of eye movement control and that it is also essential to an account of how organisms, including Man, build and maintain knowledge of their relationship to the external visual world. The eye would seem to provide a uniquely favourable system in which to study the way in which information derived within the brain about motor actions may interact with signals flowing in from peripheral receptors. The review is constructed in relatively independent sections that deal with particular topics. It ends with a fairly brief piece in which the author sets out some personal views about what has been achieved recently and what most immediately needs to be done. It also suggests some lines of study that appear to the author to be important for the future.

scholarly journals Humanin expression in skeletal muscles of patients with chronic progressive external ophthalmoplegia

2006 ◽  
Vol 51 (6) ◽  
pp. 555-558 ◽  
Author(s):  
Tesseki Kin ◽  
Kazuma Sugie ◽  
Makito Hirano ◽  
Yu-ichi Goto ◽  
Ichizo Nishino ◽  
...  
Keyword(s):  
Skeletal Muscles ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia

Disorders Affecting the Extraocular Muscles

2008 ◽  
Author(s):  
Agnes Wong
Keyword(s):  
Mitochondrial Dna ◽  
Lactic Acidosis ◽  
Clinical Features ◽  
Point Mutations ◽  
Extraocular Muscles ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia ◽  
Ragged Red Fibers ◽  
Parking Lot ◽  
A3243g Mutation

Chronic progressive external ophthalmoplegia (CPEO) occurs in 90% of patients with mitochondrial myopathy. It is characterized by a slowly progressive ptosis and ophthalmoplegia. The ophthalmoplegia is usually preceded by ptosis for months to years, and downgaze is usually intact. Kearns-Sayre Syndrome is a subtype of chronic progressive external ophthalmoplegia. Most cases are sporadic and associated with single deletions of mitochondrial DNA. Ragged-red fibers are seen on light microscopy (using modified Gomori trichrome stain). ■ Due to accumulation of enlarged mitochondria under the sarcolemma of affected muscles ■ Found in skeletal muscles, orbicularis, and extraocular muscles ■ On electron microscopy, the mitochondria contain paracrystalline (“parking lot”) inclusions and disorganized cristae that are sometimes arranged concentrically. 1. Muscle biopsy (e.g., deltoid) 2. ERG 3. Electrocardiogram (EKG) 4. Genetic testing There is no effective treatment for CPEO. Maintaining a high-lipid, low-carbohydrate diet, taking co-enzyme Q10, biotin, or thiamine, and avoiding medications such as valproate and phenobarbital may be helpful. ■ MELAS stands for mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes. ■ Maternally inherited; caused by point mutations of mitochondrial DNA (A3243G mutation accounts for about 80% of all cases) ■ Clinical features 1. Strokelike episodes before age 40 (hallmark feature) 2. Encephalopathy characterized by developmental delay, seizures, or dementia 3. Mitochondrial dysfunction manifested as lactic acidosis or ragged-red fibers 4. Ophthalmoplegia 5. Optic atrophy and pigmentary retinopathy 6. Diabetes mellitus and hearing loss ■ MNGIE stands for mitochondrial neuro-gastrointestinal encephalomyopathy. ■ Autosomal recessive; caused by mutations in the nuclear gene ECGF1, resulting in thymidine phosphorylase deficiency, which in turn causes deletions, duplications, and depletion of mitochondrial DNA ■ Clinical features: ophthalmoplegia, peripheral neuropathy, leukoencephalopathy, and gastrointestinal symptoms (recurrent nausea, vomiting, or diarrhea) with intestinal dysmotility SANDO stands for sensory ataxic neuropathy, dysarthria, and ophthalmoplegia. It is sporadic and is caused by multiple deletions of mitochondrial DNA.

scholarly journals Polyneuronal Innervation of Single Muscle Fibers in Cat Eye Muscle: Inferior Oblique

2009 ◽  
Vol 101 (6) ◽  
pp. 2815-2821 ◽  
Author(s):  
Diana M. Dimitrova ◽  
Brian L. Allman ◽  
Mary S. Shall ◽  
Stephen J. Goldberg
Keyword(s):  
Skeletal Muscles ◽  
Neuromuscular Disorders ◽  
Muscle Fibers ◽  
Single Muscle ◽  
Nerve Branch ◽  
Eye Muscle ◽  
Bipolar Electrodes ◽  
Muscle Nerve ◽  
Positive Results ◽  
Polyneuronal Innervation

Single muscle fibers with multiple axonal endplates (multiply innervated fibers) are normally present in adult extraocular muscles (EOMs), while most other mammalian skeletal muscles contain fibers with a single myoneural junction. Recent findings by others led us to investigate for the presence of polyneuronal innervation (innervation of a single muscle fiber by >1 motoneuron) in the inferior oblique (IO) muscle of pentobarbital anesthetized cats. The IO muscle nerve branches, as they coursed through the orbit, were further divided for independent or simultaneous electrical stimulation with bipolar electrodes. Four of five established tests for polyneuronal innervation gave positive results. The sum of the twitch (1) and tetanic (2) tensions in response to individual nerve branch stimulation was greater than that for simultaneous (whole) nerve stimulation. The summed electromyographic (EMG) responses (3) gave a similar positive result. The result for crossed tetanic potentiation (4) was negative for polyneuronal innervation while the crossed fatigue (5) test was positive. These results are consistent with recent studies. That the EOMs exhibit polyneuronal innervation further explains the eye-movement system's functional integrity during some neuromuscular disorders as well as its ability to operate with precision after the loss of numerous motoneurons.

The sparing of extraocular muscle in dystrophinopathy is lost in mice lacking utrophin and dystrophin

1998 ◽  
Vol 111 (13) ◽  
pp. 1801-1811 ◽  
Author(s):  
J.D. Porter ◽  
J.A. Rafael ◽  
R.J. Ragusa ◽  
J.K. Brueckner ◽  
J.I. Trickett ◽  
...  
Keyword(s):  
Duchenne Muscular Dystrophy ◽  
Muscular Dystrophy ◽  
Extraocular Muscle ◽  
Skeletal Muscles ◽  
Extraocular Muscles ◽  
Mdx Mouse ◽  
Mdx Mice ◽  
Fiber Types ◽  
Eye Muscle ◽  
Muscle Sparing

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.

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