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Shi X, Zhang J, Shi G, Zhu J. Mesencephalic trigeminal nucleus neurons with collaterals to both eyelid and masseter muscles shown by fluorescent double-labeling, revealing a potential mechanism for Marcus Gunn Syndrome. PLoS One 2023; 18:e0293372. [PMID: 37934736 PMCID: PMC10629631 DOI: 10.1371/journal.pone.0293372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Accepted: 10/10/2023] [Indexed: 11/09/2023] Open
Abstract
Poking palpebral conjunctiva evoked upper-eyelid retraction during ophthalmic surgery. Iatrogenic eyelid ptosis occurred if eyelid branch of lachrymal nerve was sectioned. Mesencephalic trigeminal nucleus (Vme) neurons were labeled when tracer injected into lachrymal nerve innervating eyelid Mueller's muscle. Masseter afferent Vme neurons projecting to oculomotor nucleus (III) was observed in toad and rat, which helps amphibians to stare prey when they open mouth widely to prey. We hypothesized single Vme neurons may have peripheral collaterals to both eyelid and masseter muscles. WGA-594 was injected into upper eyelid, and WGA-488 was simultaneously delivered into ipsilateral masseter muscle in the same rat. Then, double labeled Vme neurons were found under both conventional and confocal microscope. Meanwhile, contact of WGA-594 positive eyelid afferent Vme neurons with WGA-488 labeled masseter afferent ones were observed sometimes. Combined with our previous observation of oculomotor projection Vme neurons, we thought WGA-594/488 double labeled Vme cells, at least some of them, are oculomotor projecting ones. Contact between eyelid and masseter afferent Vme neurons are supposed to be electrotonically coupled, based on a line of previous studies. If exogenous or genetic factors make these Vme neurons misinterpret masseter input as eyelid afferent signals, these Vme neurons might feedforward massages to eyelid retractor motoneurons in the III. Besides, oculomotor projecting Vme neurons might be co-fired by adjacent masseter afferent Vme neurons through electrotonic coupling once the masseter muscle is activated. In these cases, Marcus Gunn Syndrome might occur. This finding leads to a new hypothesis for the Syndrome.
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Affiliation(s)
- Xue Shi
- Department of Anesthesiology, Hubei Key Laboratory of Geriatric Anesthesia & Perioperative Brain Health, and Wuhan Clinical Research Center for Geriatric Anesthesia, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jingdong Zhang
- Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Gaiping Shi
- Department of Stomatology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- School of Stomatology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Hubei Province Key Laboratory of Oral and Maxillofacial Development and Regeneration, Wuhan, China
| | - Junyi Zhu
- Department of Stomatology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- School of Stomatology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Hubei Province Key Laboratory of Oral and Maxillofacial Development and Regeneration, Wuhan, China
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Hernández-Morato I, Yu VX, Pitman MJ. A review of the peripheral proprioceptive apparatus in the larynx. Front Neuroanat 2023; 17:1114817. [PMID: 36910514 PMCID: PMC9998684 DOI: 10.3389/fnana.2023.1114817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Accepted: 01/19/2023] [Indexed: 03/14/2023] Open
Abstract
The larynx is an organ of the upper airway that participates in breathing, glutition, voice production, and airway protection. These complex functions depend on vocal fold (VF) movement, facilitated in turn by the action of the intrinsic laryngeal muscles (ILM). The necessary precise and near-instantaneous modulation of each ILM contraction relies on proprioceptive innervation of the larynx. Dysfunctional laryngeal proprioception likely contributes to disorders such as laryngeal dystonia, dysphagia, vocal fold paresis, and paralysis. While the proprioceptive system in skeletal muscle derived from somites is well described, the proprioceptive circuitry that governs head and neck structures such as VF has not been so well characterized. For over two centuries, researchers have investigated the question of whether canonical proprioceptive organs, muscle spindles, and Golgi tendon organs, exist in the ILM, with variable findings. The present work is a state-of-the-art review of the peripheral component of laryngeal proprioception, including current knowledge of canonical and possible alternative proprioceptive circuitry elements in the larynx.
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Affiliation(s)
- Ignacio Hernández-Morato
- Department of Otolaryngology-Head and Neck Surgery, Columbia University Irving Medical Center, New York, NY, United States
| | - Victoria X Yu
- Department of Otolaryngology-Head and Neck Surgery, Columbia University Irving Medical Center, New York, NY, United States
| | - Michael J Pitman
- Department of Otolaryngology-Head and Neck Surgery, Columbia University Irving Medical Center, New York, NY, United States
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Bohlen MO, Warren S, Mustari MJ, May PJ. Examination of feline extraocular motoneuron pools as a function of muscle fiber innervation type and muscle layer. J Comp Neurol 2016; 525:919-935. [PMID: 27588695 DOI: 10.1002/cne.24111] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 08/08/2016] [Accepted: 08/18/2016] [Indexed: 01/13/2023]
Abstract
This study explores two points related to the pattern of innervation of the extraocular muscles. First, species differences exist in the location of the motoneurons supplying multiply innervated fibers (MIFs) and singly innervated fibers (SIFs) in eye muscles. MIF motoneurons are located outside the extraocular nuclei in primates, but are intermixed with SIF motoneurons within rat extraocular nuclei. To test whether this difference is related to visual capacity and frontal placement of eyes, we injected retrograde tracers into the medial rectus muscle of the cat, a highly visual nonprimate with frontally placed eyes. Distal injections labeled smaller MIF motoneurons located ventrolaterally and rostrally within the oculomotor nucleus (III). More central injections also labeled a separate population of larger cells located dorsally in III. Thus, the cat shares with the nocturnal rat the feature of having MIF motoneurons located within the bounds of III. On the other hand, just as with monkeys, cats show segregation of the MIF and SIF medial rectus motoneuron pools, albeit in a different pattern. Second, extraocular muscles are divided into two layers; the inner, global layer inserts into the sclera, and the outer, orbital layer inserts into the connective tissue pulley. To test whether these layers are supplied by anatomically discrete motoneuron pools, we injected tracer into the orbital layer of the cat lateral rectus muscle. No evidence of either morphological or distributional differences was found, suggesting that the functional differences in these layers may be due mainly to their orbital anatomy, not their innervation. J. Comp. Neurol. 525:919-935, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Martin O Bohlen
- Program in Neuroscience, University of Mississippi Medical Center, Jackson, Mississippi, 39216
| | - Susan Warren
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, 39216
| | - Michael J Mustari
- National Primate Research Center, University of Washington, Seattle, Washington, 98195
| | - Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, 39216.,Department of Ophthalmology, University of Mississippi Medical Center, Jackson, Mississippi, 39216.,Department of Neurology, University of Mississippi Medical Center, Jackson, Mississippi, 39216
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Eye proprioception may provide real time eye position information. Neurol Sci 2012; 34:281-6. [PMID: 22872063 DOI: 10.1007/s10072-012-1172-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2012] [Accepted: 07/24/2012] [Indexed: 12/21/2022]
Abstract
Because of the frequency of eye movements, online knowledge of eye position is crucial for the accurate spatial perception and behavioral navigation. Both the internal monitoring signal (corollary discharge) of eye movements and the eye proprioception signal are thought to contribute to the localization of the eye position in the orbit. However, the functional role of these two eye position signals in spatial cognition has been disputed for more than a century. The predominant view proposes that the online analysis of eye position is exclusively provided by the corollary discharge signal, while the eye proprioception signal only plays a role in the long-term calibration of the oculomotor system. However, increasing evidence from recent behavioral and physiological studies suggests that the eye proprioception signal may play a role in the online monitoring of eye position. The purpose of this review is to discuss the feasibility and possible function of the eye proprioceptive signal for online monitoring of eye position.
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Abstract
Pathological forms of nystagmus and their visual consequences can be treated using pharmacological, optical, and surgical approaches. Acquired periodic alternating nystagmus improves following treatment with baclofen, and downbeat nystagmus may improve following treatment with aminopyridines. Gabapentin and memantine are helpful in reducing acquired pendular nystagmus due to multiple sclerosis. Ocular oscillations in oculopalatal tremor may also improve following treatment with memantine or gabapentin. The infantile nystagmus syndrome (INS) may have only a minor impact on vision if "foveation periods" are well developed, but symptomatic patients may benefit from treatment with gabapentin, memantine, or base-out prisms to induce convergence. Several surgical therapies are also reported to improve INS, but selection of the optimal treatment depends on careful evaluation of visual acuity and nystagmus intensity in various gaze positions. Electro-optical devices are a promising and novel approach for treating the visual consequences of acquired forms of nystagmus.
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Kumar A, Shetty S, Vijayalakshmi P, Hertle RW. Improvement in visual acuity following surgery for correction of head posture in infantile nystagmus syndrome. J Pediatr Ophthalmol Strabismus 2011; 48:341-6. [PMID: 21261243 DOI: 10.3928/01913913-20110118-02] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 11/23/2010] [Indexed: 11/20/2022]
Abstract
PURPOSE To report the effect of the abnormal head posture (AHP) correcting procedures on the visual acuity improvement in patients with infantile nystagmus syndrome (INS) and the visual acuity improvement outcomes in different AHP correcting surgeries in INS. METHODS This was a prospective, non-randomized, interventional study. Twenty-eight patients underwent the Anderson-Kestenbaum procedure or the modified Anderson procedure with or without tenotomy of at least one horizontal recti for correction of AHP. Best-corrected binocular null zone acuity and degree of AHP was recorded preoperatively and compared with those done 1 month postoperatively. RESULTS The average null zone logarithm of the minimum angle of resolution acuity was 0.42 preoperatively, which improved significantly to 0.33 postoperatively (P = .002). The AHP ranged from 10° to 40° (mean: 20.89°), which improved significantly to a mean of 3.21° (P = .000). No significant difference (P = .65) was found in the visual acuity improvement among patients who underwent the Anderson-Kestenbaum procedure or the modified Anderson procedure with or without tenotomy. No significant difference in the visual acuity improvement was seen in patients who underwent tenotomy of at least one horizontal rectus muscle along with the modified Anderson procedure compared to those who underwent the modified Anderson procedure alone (P = .28). CONCLUSION The procedures used mainly for correction of AHP in INS do yield significant improvement in the visual acuity. This improvement is seen in patients undergoing surgery for both horizontal and vertical AHP.
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Affiliation(s)
- Anand Kumar
- Department of Pediatric Ophthalmology and Strabismus, Bombay City Eye Institute and Research Centre, Mumbai, India
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Abstract
We review current concepts of nystagmus and saccadic oscillations, applying a pathophysiological approach. We begin by discussing how nystagmus may arise when the mechanisms that normally hold gaze steady are impaired. We then describe the clinical and laboratory evaluation of patients with ocular oscillations. Next, we systematically review the features of nystagmus arising from peripheral and central vestibular disorders, nystagmus due to an abnormal gaze-holding mechanism (neural integrator), and nystagmus occurring when vision is compromised. We then discuss forms of nystagmus for which the pathogenesis is not well understood, including acquired pendular nystagmus and congenital forms of nystagmus. We then summarize the spectrum of saccadic disorders that disrupt steady gaze, from intrusions to flutter and opsoclonus. Finally, we review current treatment options for nystagmus and saccadic oscillations, including drugs, surgery, and optical methods. Examples of each type of nystagmus are provided in the form of figures.
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Affiliation(s)
- Matthew J Thurtell
- Departments of Neurology and Daroff-Dell'Osso Laboratory, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, OH 44106, USA
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Abstract
For several forms of acquired nystagmus, animal models exist, mathematical hypotheses have been proposed, and treatments are available. What insights could acquired nystagmus provide for congenital forms of nystagmus? Acquired periodic alternating nystagmus (PAN) is caused by instability of the velocity storage mechanism for vestibular eye movements; an adaptive mechanism produces the oscillations that have a period of about 4 minutes. Surprisingly, the ability of individuals with congenital forms of nystagmus to adapt their eye movements to new visual demands has received little study. Acquired pendular nystagmus (APN) may arise from instability in the neural integrator for eye movements; identification of the neurotransmitters contributing to normal gaze holding made it possible to identify candidate drugs for treatment of APN. Similar knowledge of the biology underlying of congenital forms of nystagmus might similarly suggest effective drugs. Downbeat nystagmus (DBN) is caused by cerebellar disease, which includes structural lesions affecting the flocculus and paraflocculus, and calcium channelopathies, such as episodic ataxia type 2 (EA2), for which a mouse model and effective treatment is available. Since some congenital forms of nystagmus are genetic in origin, then the possibility arises that they may be caused by a channelopathy, a hypothesis that suggests novel drugs for evaluation in randomized controlled trials.
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Affiliation(s)
- R John Leigh
- Department of Neurology, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106-5040, USA.
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Kalla R, Spiegel R, Wagner J, Rettinger N, Jahn K, Strupp M. [Pharmacotherapy of central oculomotor disorders]. DER NERVENARZT 2009; 79:1377-8, 1380-2, 1384-5. [PMID: 18633586 DOI: 10.1007/s00115-008-2516-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Nystagmus causes blurred vision due to oscillopsia, as well as impaired balance. Depending on etiology, additional cerebellar and brain stem signs may occur. We present the current pharmacotherapy of the most common forms of central nystagmus: downbeat nystagmus (DBN), upbeat nystagmus (UBN), acquired pendular nystagmus (APN), and congenital nystagmus (CGN). Recommended medical therapies are aminopyridines (4-AP) for DBN and UBN, gabapentin and memantine for CGN and APN, and baclofen for periodic alternating nystagmus (PAN).
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Affiliation(s)
- R Kalla
- Neurologische Klinik, Klinikum Grosshadern Ludwig-Maximilians-Universität (LMU) München, Marchioninistr. 15, 81377, München.
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Zhang M, Wang X, Goldberg ME. Monkey primary somatosensory cortex has a proprioceptive representation of eye position. PROGRESS IN BRAIN RESEARCH 2009; 171:37-45. [PMID: 18718280 DOI: 10.1016/s0079-6123(08)00606-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
The visual system is tied to the retina. Because the eyes move in the orbit, and the head moves on the body, accurate location of an object in extrapersonal space cannot simply result from a visual signal. Instead, the retinal signal must be combined with an estimate of where the eyes are in the orbit, and where the head is in space, to calculate where that object is relative to the observer. There is abundant evidence for eye position signals in various areas of the visual cortex. However, the source of that eye position signal is unknown. Estimates of eye position can arise from two different sources. One is outflow, an 'efference copy' or 'corollary discharge' which might arise from some eye position signal used to specify eye position for the eye muscles. The second source is inflow, a direct proprioceptive signal from the muscles themselves. Nevertheless, neither a proprioceptive representation of eye position nor corollary discharge of a motor command for eye position has ever been demonstrated unambiguously in the cerebral cortex. We recently discovered the neuronal representation of proprioceptive eye position signal in monkey primary somatosensory cortex.
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Affiliation(s)
- Mingsha Zhang
- Mahoney Center for Brain and Behavior, Department of Neuroscience, Columbia University College of Physicians and Surgeons, and the New York State Psychiatric Institute, New York, NY, USA.
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Histochemical characterisation of trigeminal neurons that innervate monkey extraocular muscles. PROGRESS IN BRAIN RESEARCH 2009. [PMID: 18718277 DOI: 10.1016/s0079-6123(08)00603-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register]
Abstract
Sensory trigeminal innervation is a consistent feature of extraocular muscles across species, in spite of a variable occurrence of muscle spindles. We studied the histochemical properties of trigeminal ganglion (TG) cells projecting to the extraocular eye muscles to obtain more information about their function. In monkey TG neurons were retrogradely filled by tracer injections (cholera toxin subunit B; wheat-germ agglutinin) into the belly or myotendinous junction of eye muscles; one conjunctival injection served as a control. Retrogradely labelled TG neurons were processed for the presence of parvalbumin (PV), substance P (SP), or nitric oxide synthase (NOS) by double-immunofluorescence. The results indicate that approximately 10% of trigeminal afferents to all parts of the eye muscle are PV-positive, whereas around 20% are SP-positive. Twice as many SP-positive TG projection neurons were counted after a conjunctival tracer injection, presumably relaying nociceptive signals. A surprisingly large population of NOS-positive TG cells (30%) was found only after distal tracer injections. Up to now none of these TG cell groups could be related to the palisade endings located at the myotendinous junction.
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Wang X, Zhang M, Cohen IS, Goldberg ME. The proprioceptive representation of eye position in monkey primary somatosensory cortex. Nat Neurosci 2007; 10:640-6. [PMID: 17396123 DOI: 10.1038/nn1878] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Accepted: 03/08/2007] [Indexed: 11/08/2022]
Abstract
The cerebral cortex must have access to an eye position signal, as humans can report passive changes in eye position in total darkness, and visual responses in many cortical areas are modulated by eye position. The source of this signal is unknown. Here we demonstrate a representation of eye position in monkey primary somatosensory cortex, in the representation of the trigeminal nerve, near cells with a tactile representation of the contralateral brow. The neurons have eye position signals that increase monotonically with increasing orbital eccentricity from near the center of gaze, with directionally selectivity tuned in a Gaussian manner. All directions of eye position are represented in a single hemisphere. The signal is proprioceptive, because it can be obliterated by anesthetizing the contralateral orbit. It is not related to foveal or peripheral visual stimulation, and it represents the position of the eye in the head and not the angle of gaze in space.
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Affiliation(s)
- Xiaolan Wang
- Mahoney Center for Brain and Behavior, Center for Neurobiology and Behavior, Columbia University College of Physicians and Surgeons, and the New York State Psychiatric Institute, 1051 Riverside Drive, Unit 87, New York, New York 10032, USA
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Dancause N, Taylor MD, Plautz EJ, Radel JD, Whittaker T, Nudo RJ, Feldman AG. A stretch reflex in extraocular muscles of species purportedly lacking muscle spindles. Exp Brain Res 2007; 180:15-21. [PMID: 17216145 PMCID: PMC3230225 DOI: 10.1007/s00221-006-0833-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 12/13/2006] [Indexed: 12/23/2022]
Abstract
It is generally assumed that proprioceptive feedback plays a crucial role in limb posture and movement. However, the role of afferent signals from extraocular muscles (EOM) in the control of eye movement has been a matter of continuous debate. These muscles have atypical sensory receptors in several species and it has been proposed that they are not supported by stretch reflexes. We recorded electromyographic activity of EOM during passive rotations of the eye in sedated rats and squirrel monkeys and observed typical stretch reflexes in these muscles. Results suggest that there is a similarity in the reflexive control of limb and eye movement, despite substantial differences in their biomechanics and sensory receptors. Like in some limb skeletal muscles, the stretch reflex in EOM in the investigated species might be mediated by other length-sensitive receptors, rather than muscle spindles.
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Affiliation(s)
- Numa Dancause
- Department of Neurology, University of Rochester Medical Center, 601 Elmwood Ave, Box 673, Rochester, NY 14642, USA.
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von Bartheld CS, Fritzsch B. Comparative analysis of neurotrophin receptors and ligands in vertebrate neurons: tools for evolutionary stability or changes in neural circuits? BRAIN, BEHAVIOR AND EVOLUTION 2006; 68:157-72. [PMID: 16912469 DOI: 10.1159/000094085] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
To better understand the role of multiple neurotrophin ligands and their receptors in vertebrate brain evolution, we examined the distribution of trk neurotrophin receptors in representatives of several vertebrate classes. Trk receptors are largely expressed in homologous neuronal populations among different species/classes of vertebrates. In many neurons, trkB and trkC receptors are co-expressed. TrkB and trkC receptors are primarily found in neurons with more restricted, specialized dendritic and axonal fields that are thought to be involved in discriminative or 'analytical' functions. The neurotrophin receptor trkA is expressed predominantly in neurons with larger, overlapping dendritic fields with more heterogeneous connections ('integrative' or 'modulatory' systems) such as nociceptive and sympathetic autonomic nervous system, locus coeruleus and cholinergic basal forebrain. Surveys of trk receptor expression and function in the peripheral nervous system of different vertebrate classes reveal trends ranging from dependency on a single neurotrophin to a more complex dependency on increasing numbers of neurotrophins and their receptors, for example, in taste and inner ear innervation. Gene deletion studies in mice provide evidence for a complex regulation of neuronal survival of sensory ganglion cells by different neurotrophins. Although expression of neurotrophins and their receptors is predominantly conserved in most circuits, increasing diversity of neurotrophin ligands and their receptors and a more complex dependency of neurons on neurotrophins might have facilitated the formation of at least some new neuronal entities.
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Demer JL, Clark RA. Magnetic Resonance Imaging of Human Extraocular Muscles During Static Ocular Counter-Rolling. J Neurophysiol 2005; 94:3292-302. [PMID: 16033934 DOI: 10.1152/jn.01157.2004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The rectus extraocular muscle (EOM) pulleys constrain EOM paths. During visual fixation with head immobile, actively controlled pulleys are known to maintain positions causing EOM pulling directions to change by one-half the change in eye position. This pulley behavior is consistent with Listing's law (LL) of ocular torsion as observed during fixation, saccades, and pursuit. However, pulley behavior during the vestibulo-ocular reflex (VOR) has been unstudied. This experiment studied ocular counter-rolling (OCR), a static torsional VOR that violates LL but can be evoked during MRI. Tri-planar MRI was performed in 10 adult humans during central target fixation while positioned in right and left side down positions known to evoke static OCR. EOM cross-sections and paths were determined from area centroids. Paths were used to locate pulleys in three dimensions. Significant ( P < 0.025) counter-rotational repositioning of the rectus pulley arrays of both orbits was observed in the coronal plane averaging 4.1° (maximum, 8.7°) from right to left side down positions for the inferior, medial, and superior rectus pulleys. There was a trend for the lateral rectus averaging 1.4°. Torsional shift of the rectus pulley array was associated with significant contractile cross-section changes in the superior and inferior oblique muscles. Torsional rectus pulley shift during OCR, which changes pulling directions of the rectus EOMs, correlates with known insertions of the oblique EOM orbital layers on rectus pulleys. The amount of pulley reconfiguration is roughly one-half of published values of ocular torsion during static OCR, an arrangement that would cause rectus pulling directions to change by less than one-half the amount of ocular torsion.
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Affiliation(s)
- Joseph L Demer
- Department of Ophthalmology, UCLA, Los Angeles, CA 90095-7002, USA.
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