EOMs Movements

All eye movements can be described as rotations around one or more axes

Fick’s Axes

According to Fick, …

• These axes divide the globe into quadrants and intersect at the center of rotation, a fixed non-moving point

• Eye rotate around its fixed point located 13.5 mm behind the cornea (varies in ametropia - most posterior in myopia, more anterior in hyperopia)

Fick’s Axes: X-axis

Horizontal or transverse axis

Runs from nasal to temporal

Fick’s Axes: Y-axis

Sagittal axis

Runs from anterior pole to the posterior pole

Fick’s Axes: Z-axis

Vertical axis

Runs from superior to inferior

What is the movement horizontal X axis responsible for?

Up/down

What is the movement vertical Z axis responsible for?

Medial/lateral

What is the movement sagittal Y axis responsible for?

Internal/external

What is duction?

Movements involving just one eye

Rotation around the vertical axis move the anterior pole of globe

Medially- adduction (“adentro”)

Laterally- abduction

Rotation around the horizontal axis move the anterior pole of globe

Up- elevation(supraduction)

Down- depression (infraduction)

Torsions or cyclorotations are rotations around the sagittal axis

Intorsion (incyclorotation)- nasally rotation

Extorsion (excyclorotation)- temporally rotation

What is vergence?

Movements involving both eyes (same action at the same time)

Are disjunctive movements (opposite directions)

• Convergence- each eye is adducted

• Divergence- each eye is abducted

What is version?

Conjugate movements

Dextroversion

Right gaze (lateral rectus in OD, medial rectus in OS)

Levoversion

Left gaze (medial rectus in OD, lateral rectus in OS)

Supraversion

Both eyes are elevated (superior rectus always works w/ inferior oblique)

Infraversion

Both eyes are depressed (inferior rectus always works w/ superior oblique)

EOM actions: Medial rectus

Primary action: Adduction

EOM actions: Lateral rectus

Primary action: Abduction

EOM actions: Superior rectus

Primary action: Elevation

Secondary action: Adduction, Intorsion

EOM actions: Inferior rectus

Primary action: Depression

Secondary action: Adduction, Extorsion

EOM actions: Superior oblique

Primary action: Intorsion

Secondary action: Depression, Abduction

EOM actions: Inferior oblique

Primary action: Extorsion

Secondary action: Elevation, Abduction

Primary position of gaze

Looking straight ahead with head straight

Position of the eye with the head erect, eye focused for infinity

Secondary position of gaze

Rotations around either the vertical or horizontal axis

Tertiary position of gaze

Rotations around both vertical and horizontal axes

Agonists muscles

Making the same actions

Antagonist muscles

Making the opposite action

Agonist-Antagonist Pairs (in the same eye)

Medial rectus-lateral rectus

Superior rectus-inferior rectus

Superior oblique-inferior oblique

Paired agonists (in separate eyes)

Left medial rectus-right lateral rectus

Left lateral rectus-right medial rectus

Left superior rectus-right inferior oblique

Left inferior rectus-right superior oblique

Left superior oblique- right inferior rectus

Left inferior oblique- right superior rectus

Sherrington’s Law of reciprocal innervation

Contraction of a muscle is accompanied by a simultaneous and proportional relaxation of the antagonist

Sherrington’s Law of reciprocal innervation: Adduction

Increase contraction of the medial rectus is accompanied by the increased relaxation of the lateral rectus (antagonist)

Sherrington’s Law of reciprocal innervation: Elevation

Muscles are synergists

• Superior rectus and inferior oblique muscle contract at the same time

• Adduction of the superior rectus and abduction of the inferior oblique

• Intorsion of the superior rectus

• Extorsion of the inferior oblique

Sherrington’s Law of reciprocal innervation: Depression

Superior oblique and the inferior rectus are synergists

Sherrington’s Law of reciprocal innervation: Vertical and torsional movements

Superior oblique is the antagonist of the inferior oblique

Sherrington’s Law of reciprocal innervation: Abduction

The superior oblique is synergistic of the inferior oblique

Yoke muscles

Those muscles of the two eyes acting together to cause binocular movements

Hering’s Law of Equal Innervation

States that the innervation to the muscles of the two eyes is equal simultaneous

Strabismus

Movement is not coordinated between the two eyes and the visual axes are not straight when the patient is asked to look in primary position

• Can be congenital (suppression) or acquired (diplopia)

Brow Superior Oblique Sheat Syndrome

Inability to elevate the eye in the adducted position

Usually caused by a dysfunctional inferior oblique muscle, but also for limitation of an immobile superior oblique muscle

Congenital Brown’s Syndrome

Cause could be a short or anchored tendon

Acquired Brown’s Syndrome

Cause could be an accumulation of fluid or tissue between the trochlea and the tendon

Myasthenia Gravis

A chronic autoimmune, neuromuscular disease that causes weakness in the skeletal muscles

First clinical eye symptom is ptosis (progressive droop during the examination)

Ocular myasthenia gravis is limited to eye and lid muscles- diplopia and ptosis