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Home , Extraocular muscles

Extraocular muscles. Conjugated movements. .

Sándor Katz M.D., Ph.D. Conjugated eye movements

Requirements:

• Extraocular muscles • Innervation: CN. III., IV., VI. Precision and speed of muscle function rely on structural characteristics. Their motor innervation is well developed: 1 motor fiber/6 muscle fibers (in finger: 100-300 muscle fibers, in other muscles: 1500 muscle fibers) • Central pathways for eye movements, ensuring coordination Eye vs. Orbit

• The medial wall runs in paramedian sagittal plane.

• The lateral wall deviates laterally: 45°.

• The AP (antero- posterior) axis of the eye is parallel with the sagittal axis.

• The extraocular muscles run almost parallel with the axis of orbit. Orbit Orbit

The eyeball is attached by membranes to the capsule of the orbital fat body, and it can move in all directions in the episcleral space.

Movements are achieved by four recti and two oblique muscles. The tendons of the rectus muscles originate form a funnel-shaped ring around the optic canal: common tendinous ring. Orbit

medial rectus nasociliary superior rectus

superior oblique

lateral rectus

lacrimal nerve

frontal nerve superior oblique

medial rectus

inferior rectus

inferior oblique pes anserinus minor Possible eye movements

Sagittal axis: Internal/medial rotation External/lateral rotation (difficult to see as the pupil is round in humans). Possible eye movements

Horisontal axis: Elevation Depression Possible eye movements

Vertical axis: Abduction Adduction – CN VI.

Vertical axis: Abduction

Origin: common tendinous ring Insertion: , posterior to the limbus corneae – CN III., inferior ramus

Vertical axis: Adduction

Origin: common tendinous ring Insertion: sclera, posterior to the limbus corneae – CN. III., superior ramus

Sagittal axis: Medial rotation Vertical axis: Adduction Horisontal axis: Elevation

Origin: common tendinous ring Insertion: sclera, posterior to the limbus corneae – CN. III., inferior ramus

Sagittal axis: Lateral rotation Vertical axis: Adduction Horisontal axis: Depression

Origin: common tendinous ring Insertion: sclera, posterior to the limbus corneae – CN. IV.

Sagittal axis: Medial rotation Vertical axis: Abduction Horisontal axis: Depression

Origin: body of the Insertion: its tendon passes trough the trochlea and inserts into sclera deep to superior rectus muscle – CN. III. inferior ramus

Sagittal axis: Lateral rotation Vertical axis: Abduction Horisontal axis: Elevation

Origin: anterior part of the floor of orbit Insertion: sclera, deep to the lateral rectus muscle Binocular movements

Inferior oblique, Superior rectus Inferior oblique, Superior Rectus,Inferior oblique Superior rectus

Lateral rectus, Medial rectus Primary position Lateral rectus, Medial rectus

Superior oblique, Inferior rectus Superior oblique, Inferior Rectus,Superior oblique Inferior rectus Central pathways of eye movements

The extraocular muscles in both orbits always work together, resulting conjugated eye movements coordinated by cortical areae and brain stem’s nuclei: • Brodmann’s area 8 (middle frontal gyrus) • Superior colliculi • Paramedian areae of the reticular formation • Nucleus interstitialis Cajal • Fasciculus longitudinalis medialis

The common impulse from cortical areae and nuclei effects on the motoneurons of III., IV., VI. cranial ’ nuclei. Pathway of horisontal eye movements

• Brodmann area 8 • Through internal capsule to the reticular formation of midbrain and pons • The fibers cross between the midbrain and pons • Descending branch to the contralateral abducent nucleus • Ascending branch to the ipsilateral oculomotor nucleus via fasciculus longitudinalis medialis After injury of horisontal pathway above the midbrain the extraocular muscles are not able to move toward contralateral side. After injury of the pons they are not able to move toward ipsilateral side. Pathway of vertical eye movements

• Brodmann area 8 • Through the internal capsule to nucl. interstitialis Cajal • Fasciculus longitudinalis medialis • Motoneurons of III., IV. ’ nuclei

Injury around the cerebral aqueduct blocks looking upwards and downwards. Principles of the eye movements

The image of an object should fall to roughly identical regions of the retina in the two and should project to roughly the same part in the same visual cortex. Small differences in projections are interpreted as spatial/positional information, big differences will lead to double image formation.

Result: The movement of both eyes should be coordinated – focusing the same object. Strabismus – crossed eyes A condition in which the eyes do not properly align with each other when looking at an object. It may also be present occasionally or constantly. Strabismus can occur due to muscle dysfunction, farsightedness, problems in the brain, trauma, or infections. Risk factors include premature birth, cerebral palsy, and a family history of the condition. Symptoms of strabismus include double vision and/or . To avoid double vision, the brain may adapt by ignoring one eye in children, but not in adults. Treatment depends on the type of strabismus and the underlying cause. This may include the use of glasses and possibly surgery. Oculomotor palsy

Only superior oblique and lateral rectus muscles work. The eye is moved laterally and downwards. Levator palpebrae superioris muscle is paralyzed: the drops. Sphincter pupillae muscle is paralyzed: pupil dilatates, no light response. is paralyzed: eye focused to infinity, no acommodation. Double image. Trochlear palsy

Superior oblique muscle is paralyzed other muscles pull the effected eye medially and upwards. Double image. Abducent palsy

Lateral rectus muscle is paralyzed, other muscles pull the effected eye medially. Double image. Thank you for your attention.

References: Dr. Ákos Lukáts’s lecture, 2014 Drake: Gray’s Anatomy for Students, 2nd ed. Standring: Gray’s Anatomy, 39th ed. Radiopaedia.org SH Atlas, Anatómia III. Ágoston Szél: Klinikai Anatómia