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Motor physiology
S.A.A MORTAZAVI MD Associate professor of
ophthalmologyIsfahan university of medical sciences
2011 - 1390
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Axes of FICK X-axis a transverse
axis passing through the center of the eye at the equator
Y-axis a sagital axis passing through the pupil
Z-axis a vertical axis
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Voluntary vertical rotations of the eye occur about X axis
Voluntary horizontal rotations of the eye occur about Z axis
Involuntary torsional rotations of the eye occur about Y axis
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listing’s equatorial plane
The center of rotation and includes the
X and Z axes The Y axis is
perpendicular to this plane
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Positions of Gaze
Primary position : straight ahead Secondary positions : straight
up ,straight down, right ,left Tertiary positions : up & right, up & left,
down & right, down & left
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Arc of contact
The point of effective or physiologic insertion is the tangential point where the muscle first contacts the globe
The action of the eye muscle : a vector of force that acts at this tangential point to rotate the eye
The length of muscle actually in contact with the globe
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Monocular eye movements
Adduction:movement of the eye nasally Abduction:movement of the eye temporally Elevation (supraduction): upward rotation Depression (infraduction): downward rotation Intorsion (incycloduction):nasal rotation of
the superior portion of the vertical corneal meridian
Extorsion(excycloduction):temporal rotation of the superior portion of the vertical corneal meridian
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Agonist: the primary muscle moving the eye in a given direction
Synergist: the muscle in the same eye as the agonist that acts with the agonist to produce a given movement
Antagonist: the muscle in the same eye as the agonist that acts in the direction opposite to that of the agonist
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Sherrington’s law
Increased innervational and contraction of a given muscle are accompanied by a reciprocal decrease in innervation and contraction of its antagonist
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Binocular eye movements
Version: eye movements conjugate and the eyes move in the same direction
Vergence: eye movements disconjugate and the eyes move in opposite directions
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versions
Dextroversion : movement of both eyes to the patient’s right
Levoversion : movement of both eyes to the patient’s left
Elevation : upward rotation of both eyes Depression : downward ratation of both eyes Dextrocycloversion : both eyes rotate so that the
superior portion of the vertical corneal meridian moves to the patient’s right
Levocycloversion : movement of both eyes so that the superior portion of the vertical corneal meridian rotates to the patient’s left
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Yoke muscles
Two muscles (one in each eye ) that are the prime movers of their respective eyes in a given position of gaze
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Cardinal positions
The six positions of gaze in which one muscle of each eye is the prime mover are known as the cardinal positions of gaze
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Hering’s law
Equal and simultaneous innervation flows to yoke muscles concerned with the desired direction of gaze
Important clinical implications especially when dealing with a paralytic or restrictive strabismus
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Primary deviation: the amount of misalignment when the normal eye is fixating
Secondary deviation: the amount of misalignment when the paretic or restrictive eye is fixating
The secondary deviation is larger than the primary deviation
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vergence
Convergence: movement of both eyes nasally relative to a given position
Divergence: movement of both eyes temporally relative to a given position
Vertical vergence: less frequently encountered ,can also occur; one eye moves upward and the other downward
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Incyclovergence : a rotation of both eyes so that the superior portion of each vertical corneal meridian rotates the toward the median plane
Excyclovergence : a rotation of both eyes so that the superior portion of each vertical meridian rotates away from the median plane
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Tonic convergence :the constant innervational tone to the extraocular muscles when a person is awake and alert
Accommodative convergence of the visual axes : part of the synkinetic near reflex
Voluntary convergence : a conscious application of the near synkinesis
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