Ocular movements & visual reflexes

Muscles of the orbit

• Extraocular
  • 4 rectus
    • Superior rectus
      • oculomotor nerve
    • Inferior rectus
      • oculomotor nerve
    • Medial rectus
      • oculomotor nerve
    • Lateral rectus
      • abducen nerve
  • 2 oblique
    • Superior oblique
    • Inferior oblique
  • Levator Palpebrae Superioris (LPS)
  • Smooth muscles
    • Superior tarsal
    • Inferior tarsal
    • Orbitalis
• Intraocular
  • Sphincter pupillae
  • Dilator pupillae
  • Ciliaris

Bony orbit of the eye

• Superior
  • frontal bone
• Inferior
  • maxilla
• Medial
  • Lacrimal bone
• Lateral
  • zygomatic bone

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Movements of the eyeball

• controlled by the 4 rectus and 2 oblique extraocular muscles
  • function
    • allow us to follow moving object
    • maintain foveal fixation
    • binocular vision
    • maintain shape of eyeball
  • when the movements of 2 eyes are not coordinated
    • images of same area of visual fied not focused on same areas of retina
      • producing DIPLOPIA
    • usually due to weakness/paralysis of extraocular muscles
      • confenital/acquired, one eye rotated medially/laterally
        • producing strabismus/squint

A – right medial displacement

• muscle paralysed: lateral rectus

B – right lateral displacement

• muscle paralysed: medial rectus

C – superior displacement

D – inferior displacement

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Monoular movements

• Movement of 1 eye to 1 direction = Duction
  • medially: adduction
  • laterraly: abduction
  • superiorly: supraduction
  • inferiorly: infraduction
• Vertical meridian-torsional movement
  • nasal rotation, medially along antero-posterior axis
    • intortion
  • temporal rotation, laterally along antero-posterior axis
    • extortion

• Agonist
  • primary muscle that moves an eye in a given direction
  • eg. abduction by lateral rectus
• Synergist
  • muscle in the same eye that moves the eye in the same direction as the agonist (support the same movement)
  • eg. abduction supported by superior & inferior oblique
• Antagonist
  • muscle in the same eye that moves the eye in the opposite direction of the agonist is the antagonist
  • eg. medial rectus is an antagonist to abduction by lateral rectus

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Binocular movements

• Movements are either conjugate (versions) or disconjugate
  • movement of 2 eyes in the same direction: version
• Levoversion
  • eyes moving in the same direction
  • eg. right eye adduction, left eye abducting
• Convergence
  • both eyes look towards the nose
• Yoke muscles
  • primary muscles in each eye that perform the version
  • eg. when looking to the left, left eye perform abduction by lateral rectus muscle. right eye perform adduction by medial rectus muscle. Yoke muscles: lateral and medial rectus muscle.

Visual axis

• Horizontal plane
  • Primary plane of action
  • Movements are 90 degrees to plane
    • Elevation
    • Depression
• Vertical plane
  • 2ndary plane of action
  • Movements are 90 degrees to plane
    • Adduction
    • Abduction
• Antero-posterior plane
  • 3rd plane of action
  • Movements are 90 degress to plane
    • Intortion
    • Extortion

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Extraocular muscles

Rectus muscles

• Common origin
  • All arise from posterior part of orbit
    • from a common tendinous ring
    • that surrounds optic canal, superior orbital fissure
• Insertion into sclera
  • inserted into sclera
    • 6mm behind sclero-corneal junction

• If not following eyeball plane
  • what are the muscles not in allignment?

Levator Palpebrae Superioris (LPS) muscle

• Action: elevates upper eyelid
• Arise from
  • Lesser wing of sphenoid
• Partially supplied by
  • Somatic nerve (3rd cranial nerve)
  • Autonomic (sympathetic – involuntary smooth muscles)
    • Superior tarsal
      • deep part of LPS
    • Inferior tarsal
      • connects inferior tarsal plate to fascia around inferior rectus
      • both these, innervated by sympathetic nerves = responsible for widely opening the eyelids in response to fear
    • Orbitalis
      • small smooth muscles bridging inferior orbital fissure
      • may compress inferior ophthalmic nerves –making eyeballs prominent
• Aponeurosis divides LPS into 3 layer
  • Superficial – skin of upper eyelid
  • Middle – tarsal plate of upper eyelid
  • Deep – superior conjunctival fornix

Superior Oblique muscle

• Arise from
  • body of sphenoid bone
    • medial to optic canal
    • goes medially, then ends in a tendon
    • attached to a pulley: trochlea
    • then suddenly runs backward & laterally (change in direction)
    • inserted to upper & lateral quadrant of eyeball

Inferior oblique muscle

• Arise from
  • medial part of floor
    • winds round the eyeball laterally & backwards
    • inserted to lateral part of sclera

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Movements of the extraocular muscles

Superior rectus	1 – elevation 2 – intortion 3 – adduction
Inferior rectus	1 – depression 2 – adduction 3 – extortion
Medial rectus	1- adduction
Lateral rectus	1- abduction
Superior oblique	1 – intortion 2 – depression 3 – abduction
Inferior oblique	1 – extortion 2 – elevation 3 – abduction

*know the primary, secondary and tertiery movements (refer table)

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Extraocular muscle disorders

Complete 3rd nerve palsy

• Muscle affected
  • medial rectus
• Clinical Presentation
  • lateral strabismus
    • Medial rectus affected
  • diplopia
    • eye cannot be moved upwards, medially & downwards
  • ptosis
    • LPS affected
  • *dilated pupil (light reflex sluggish/absent)
    • sphincter pupillae affected
  • loss of accommodation
• Cause
  • diabetes
  • atherosclerosis
  • tumours
  • haemorrhage

4th nerve palsy

• Muscle affected
  • Superior oblique
• Diplopia
  • difficulty in turning the eyes downwards & laterally while walking down stairs

6th nerve palsy

• Muscle affected
  • lateral rectus
• Medial strabismus
  • cannot turn eye laterally
• Cause
  • facial infection –> cavernous sinus –> infect 6th nerve supplying lateral rectus –> paralysis –> medial strabismus

Extra:

• Sphincter pupillae
  • 3rd nerve
• Dilator pupillae
  • sympathetic nerve

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Light reflex

• Useful for gauging brain stem function
• Normally pupils contrict equally
• Direct light reflex
  • Each pupil constricts with light shone into that eye
• Consensual pupillary reflex
  • Each pupil constricts with light shone into the OTHER eye

 http://library.med.utah.edu/kw/hyperbrain/anim/reflex.html

Pupillary light reflex pathway

• Light stimulates retinal photoreceptors
• Afferent fibres transmitted via optic nerve
• Undergo hemi-decussation at optic chiasma
• Exit from optic tract before lateral geniculate body
  • lateral geniculate body = vision
• Enters midbrain
  • via brachium of superior colliculus
• Synapse at pretectal nucleus
• Fibres go to same-sided & contralateral Edinger –Westphal nuclei
  • 3rd nerve
• Efferent fibres travel via 3rd nerve
• Synapse at ciliary ganglion
  • Post-ganglionic fibres –> short ciliary nerve
• Innervate left & right sphincter muscles
  • constriction of pupil
  • Same sided: direct
  • Contralateral: consensual

• Pretectal nucleus
  • main station for light reflex
• Edinger-Westphal nucleus
  • parasympathetic nucleus of oculomotor nerve
• Sphincter muscles
  • efferent parasympathetic fibres
• Nerve
  • before Edinger-Westphal – Optic nerve (afferent)
  • after Edinger-Westphal – Oculomotor nerve (efferent)

Anatomical bases for consensual light reflex

• From pretectal, fibres sent to both Edinger-Westphal nucleus –> pupillary constriction in both eyes

Lack of / abnormal pupillary reflex

• Optic nerve damage
  • sensory component
  • ipsilateral direct reflex loss
  • contralateral direct reflex intact
• Oculomotor nerve damage
  • motor component
  • damaged side both direct & consensual reflex loss
  • opposite side both direct & consensual reflex intact
• Argyll Robertson pupil
  • pupil does not react to light, but will react to near accommodation

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Pathway of sympathetic dilatation of pupil

• Less well-dfined
• Pathway:
  • Originates in hypothalamus
  • Descends uncrossed to T1
    • inferior cervical ganglion
    • medial cervical ganglion (stellate)
    • superior cervical ganglion
  • Exit from spinal cord via perivertebral sympathetic chain
  • Synapse in the superior cervical ganglion
  • Join ophthalmic division of trigeminal nerve
    • via carotid plexus
  • Innervate dilator pupillae of the iris
    • via the long ciliary nerve
    • (short ciliary nerve innervate sphincter pupillae)
• If paralysis
  • miosis (constriction of pupil)
    • seen in horner’s syndrome

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Accommodation reflex

• Reflex action of the eye in response to focusing on a near object
• Coordinated changes in
  • convergence
    • medial rectus
    • Optic nerve (afferent limb) –> optic tract –> visual cortex –> long association fibre –> frontal eye field –> corticonuclear fibres (pyramidal tract) –> oculomotor nerve (efferent limb) –> contraction of medial rectus of both eyes
  • lens shape
    • ciliary muscles
    • ciliary muscle contracts, suspensory ligaments relaxed –> making lens more convex – shortening its focal length
  • pupil size
    • sphincter pupillae
    • Edinger-Westphal nucleus –> oculomotor nerve (efferent limb) –> ciliary ganglion –> short ciliary nerve –> ciliary muscle constraction –> sphincter pupillae muscle contraction
    • pupil contricts to prevent diverging light rays from hitting the periphery of the retina & producing blurred image
• Components
  • Afferent: Optic nerve
  • Cell station: Multisynaptic
  • Efferent: Oculomotor
• Oculomotor nerve supplies these
  • smooth muscles
    • ciliaris
    • sphincter pupillae
  • medial rectus

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Other reflexes

Corneal reflex

• Important to detect 7th nerve palsy
  • Differential diagnosis: acoustic neuroma
• Components
  • Afferent – V1
  • Cell station – medial longitudinal fasciculus
  • Efferent – Facial nerve (orbicularis)
• Pathway
  • light touch of cornea/conjunctiva –> ophthalmic (trigeminal) nerve (Afferent limb) –> sensory nucleus of 5th CN (pons) –> medial longitudinal fasciculus –> motor nucleus of 7th CN –> facial nerve (efferent limb) –> orbicularis oculi (closure of eyelids)
• Which reflex is done to test the 7th CN?
  • corneal reflex and conjunctival reflex
  • bilateral blinking seen
• Tumour over the 8th CN, can compress the intercostal acoustic meatus (containing 7th CN) –> corneal reflex loss

Visual body reflex

• Optic nerve –> optic tract –> superior colliculus –> tectospinal & tectobulbar tract –> automatic movements of the head, neck & body towards the source of visual stimulus

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Functional components

Horner’s Syndrome

• Cause
  • pancoast tumour compressing the sympathetic nerves at T1 level
• Clinical features
  • Ptosis (drooping of eyelid)
  • Enophthalmus (reduced prominence of eyeball)
  • Anhydrosis
  • Miosis (Constriction of pupil)