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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