1.2e Strabismus

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OBJECTIVES Enumerate the EOMs - O, I, A Anatomy and physiology Yoke Perform an eye exam Types of strabismus EXTRAOCULAR MUSCLES 4 Recti muscles − Superior rectus − Inferior rectus − Medial rectus − Lateral rectus 2 Oblique muscles − Superior oblique − Inferior oblique Levator palpebrae superioris

FICK'S AXES X (horizontal) axis − Lies horizontally when head is upright − Elevation / Depression Y (antero-posterior) (antero-posterior) axis − Torsional movements − Extorsion / Intorsion Z (vertica axis) − Adduction / abduction

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SUPERIOR RECTUS Around the transverse axis - rotates the eyeball upwards - Elevation (Primary action) Around the vertical axis adduction Around the anteroposterior axis Intorion

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MUSCLES CAUSING MONOCULAR MOVEMENTS Extra-ocular muscles can have primary, secondary, and tertiary actions Primary muscle action is the main and most powerful direction in which the eye moves when the muscle is contracted Secondary muscle action is the second direction in which the eye moves when that muscle is contracted, but is not the main or most important action. Tertiary muscle action is the least powerful direction in which the eye moves as a result of contraction of the muscle.

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Muscle

Primary action

MR LR SR IR SO IO

Adduction Abduction Elevation Depression Intorsion Extorsion

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SUPERIOR OBLIQUE MUSCLE Body of sphenoid above and medial to optic canal Winds around trochlea at superomedial part of orbit (functional origin) Insertion behind the equator posterosuperior quadrant Only eye muscle innervated on the outer surface of muscle belly. Retrobulbar anaesthatic block

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INFERIOR RECTUS Around the transverse axis - rotates the eyeball downwards - Depression (Primary action) Around the vertical axis  Adduction Around the anteroposterior axis Extortion

INFERIOR OBLIQUE MUSCLE Origin from orbital surface of maxilla Passes backward and laterally below inferior rectus Insertion behind equator parallel to superior oblique postero-superior quadrant The oblique muscles always course below the corresponding vertical rectus muscle

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OCULAR MOVEMENTS MONOCULAR BINOCULAR 1. Abduction 1. Version 2. Adduction 2. Vergence 3. Elevation 4. Depression 5. Intorsion 6. Extorsion

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Secondary action

Tertiary action

Intorsion Extorsion Depression Elevation

Adduction Adduction Abduction Abduction

Sherington’s law refers to Ductions (reciprocal inervation) Hering’s law refers to Versions(equal innervation to “YOKE” muscles) YOKE MUSCLES A pair pair of of muscles, one in each each eye, which move the two eyes in the same direction. Example: RLR and LMR; RMR and LLR Hering's law BEI SAMONTE ☺

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BINOCULAR VISION Eyes that work together Requirements Clear eyes Straight eyes Numbers 1 and 2 present in infancy

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 AMBLYOPIA FUNCTIONAL LOSS OF VISION due to: Strabismus aka squint, tropia, ocular deviation Anisometropia (Unequal grade of the two eyes) Visual deprivation in infancy (ex: congenital cataract)

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CLASSIFICATION OF STRABISMUS Esotropia, Exotropia, Hypertropia Congenital or acquired Accommodative or non accommodative Comitant or incomitant (non paralytic / paralytic) Alternating or monocular

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TESTS FOR OCULAR ALIGNMENT Corneal light reflection test or Hirschberg's test Prism test or Krimsky test

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 AIMS OF TREATMENT Good vision Good alignment Binocular vision if possible

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TREATMENT 1. 2. 3. •

 

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Eyeglasses Patching for amblyopia Surgery Most commonly recess-resect procedures Ductions Sherington's law of reciprocal innervation

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BEI SAMONTE ☺

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