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Extraocular Muscles. Conjugated Eye Movements. Strabismus

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Extraocular Muscles. Conjugated Eye Movements. Strabismus Extraocular muscles. Conjugated eye movements. Strabismus. 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 Orbit 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 nerve superior rectus superior oblique lateral rectus lacrimal nerve frontal nerve lacrimal gland 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 Lateral rectus muscle – CN VI. Vertical axis: Abduction Origin: common tendinous ring Insertion: sclera, posterior to the limbus corneae Medial rectus muscle – CN III., inferior ramus Vertical axis: Adduction Origin: common tendinous ring Insertion: sclera, posterior to the limbus corneae Superior rectus muscle – 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 Inferior rectus muscle – 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 Superior oblique muscle – CN. IV. Sagittal axis: Medial rotation Vertical axis: Abduction Horisontal axis: Depression Origin: body of the sphenoid bone Insertion: its tendon passes trough the trochlea and inserts into sclera deep to superior rectus muscle Inferior oblique 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 nerves’ 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. cranial nerves’ 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 eyes 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 eye strain. 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 eyelid drops. Sphincter pupillae muscle is paralyzed: pupil dilatates, no light response. Ciliary muscle 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.
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