Cranial nerve innervation of ocular structures
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Cranial Nerve Innervation of Ocular Structures. You’ve Got a Lot of Nerve(s)!. Introduction. Orbital structures are innervated by cranial nerves (CNs) II, III, IV, V, VI, and VII

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Cranial Nerve Innervation of Ocular Structures

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Cranial nerve innervation of ocular structures

Cranial Nerve Innervation of Ocular Structures

You’ve Got a Lot of Nerve(s)!


Introduction

Introduction

  • Orbital structures are innervated by cranial nerves (CNs) II, III, IV, V, VI, and VII

  • Motor functions of the striated muscle are controlled by CN III, the oculomotor nerve; CN IV, the trochlear nerve; CN VI, the abducens nerve; and CN VII, the facial nerve

  • The trigeminal nerve, CN V, carries the sensory supply from the orbital structures

  • CN II, the optic nerve, carries visual information


The nervous system

The Nervous System

  • Afferent fibers bring information into the central nervous system (CNS)—these fibers generally have specialized nerve endings that respond to sensation producing stimuli such as touch, pressure, temperature, and pain

  • Information processing within the brain and spinal cord necessitates communication between different areas of the CNS through fiber tracts—a fiber tract may also be called a fasiculus, a peduncle, or a brachium

  • The portion of the cranial nerve from the cell body in the nucleus to its exit from the brain stem is the fasicular portion of the nerve


The nervous system 2

The Nervous System 2

  • Efferent fibers, either somatic or autonomic, carry information from the CNS to target structures: muscles, organs, or glands

  • The efferent pathway in the somatic system usually consists of a fiber that runs the distance from the CNS to the target muscle—the autonomic pathway generally has a synapse within its pathway


Afferent pathway orbital sensory innervation

Afferent Pathway: Orbital Sensory Innervation

  • The eye is abundantly supplied with sensory nerves that carry the sensation of touch, pressure, warmth, cold, and pain

  • Sensations from the cornea, iris, conjunctiva, and sclera consist primarily of pain—even light touching of the cornea registers as irritation or pain


Trigeminal nerve

Trigeminal Nerve

  • The fibers of the trigeminal nerve (CN V) serving ocular function are sensory and originate in the innervated structures

  • The description of the pathways of these nerves begins at a particular structure and follows the nerves as they join to become larger nerves, come together in the ganglion of the fifth cranial nerve, and then exit the ganglion and enter the pons

  • Considering the nerve in this manner, will mirror the direction of the action potential and information flow in these fibers

  • The trigeminal nerve consists of three branches: 1) ophthalmic, 2) maxillary, and 3) mandibular


Ophthalmic division of cn v

Ophthalmic Division of CN V

  • The ophthalmic division of the trigeminal nerve, CN V, is formed from the following branches:

    • Nasociliary nerve

    • Frontal nerve

    • Lacrimal nerve

  • The maxillary division of the trigeminal nerve, CN V, is formed from the following branches:

    • Infraorbital nerve

    • Zygomatic nerve

  • The mandibular division of the trigeminal nerve innervates the lower face and contains both sensory and motor fibers—it enters the skull through the foramen ovale


Nasociliary nerve

Nasociliary Nerve

  • Sensory fibers from the structures in the medial canthus—caruncle, canaliculi, lacrimal sac, medial portion of the eyelids, the skin at the side of the nose—join to form the infratrochlear nerve

  • This nerve penetrates the orbital septum, enters the orbit below the trochlea, and runs along the upper border of the medial rectus

  • The anterior ethmoid nerve forms from fibers from the skin along the center of the nose, the nasal mucosa, and the ethmoid sinuses

  • The posterior ethmoid nerve forms from fibers from the ethmoid and sphenoid sinuses

  • Both nerves enter the orbit through the ethmoid foramina and join the nasociliary nerve along the orbit’s medial wall


Nasociliary nerve 2

Nasociliary Nerve 2

  • Corneal innervation is dense (three to four time that of other epithelial tissue) and three networks of nerves are formed that are located in:

    • Corneal epithelium

    • Anterior stroma (subepithelial plexus)

    • Middle of the stroma

  • Nerves from these plexi come together in the peripheral stoma and radiate out into 70 to 80 branches, becoming myelinated in the last 2 mm of the cornea

  • Some of these branches join with nerves from other anterior segment structures to form two long ciliary nerves—one on the lateral side and one on the medial side of the globe


Nasociliary nerve 3

Nasociliary Nerve 3

  • The long ciliary nerves run between the sclera and the choroid to the back of the eye and leave the eyeball at points approximately 3 mm on each side of the optic nerve

  • In addition to carrying afferent fibers out of the eye, they carry efferent sympathetic fibers into the eye to the dilator muscle

  • The long ciliary nerves then join up with the nasociliary nerve


Cranial nerve innervation of ocular structures

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Scleral nerve loops of axenfeld

Scleral Nerve Loops of Axenfeld

  • In some eyes (about 12%) the long ciliary nerve loops into the sclera from the suprachoroidal space, creating a dome-shaped elevation about 2 mm from the limbus on either the nasal or temporal side, but usually inferiorly

  • These are the scleral nerve loops (of Axenfeld)

  • Often this raised area is pigmented, usually blue or black, and should be differentiated from a melanoma

  • The nerve loop may produce pain when touched, which aids in its diagnosis


Nasociliary nerve 4

Nasociliary Nerve 4

  • The other branches leaving the cornea join other sensory nerves and enter the choroid, join with the choroidal nerves, run to the back of the eye, where they leave as 6 to 10 short ciliary nerves

  • The short ciliary nerves exit the sclera in a ring around the optic nerve and enter the ciliary ganglion—the short ciliary nerves carry sympathetic and parasympathetic fibers in addition to sensory fibers

  • The sensory fibers do not synapse, but pass through the ganglion, leaving as the sensory root of the ciliary ganglion, which then joins the nasociliary nerve


Nasociliary nerve 5

Nasociliary Nerve 5

  • In summary, the nasociliary nerve is formed by the joining of the infratrochlear nerve, the anterior and posterior ethmoid nerves, the long ciliary nerves, and the sensory root of the ciliary ganglion

  • The nasociliary nerve runs through the common tendinous ring and exits the orbit through the superior orbital fissure into the cranial cavity


Herpes zoster

Herpes Zoster

  • Herpes zoster (also knowns as shingles) is an acute CNS infection caused by the varicella-zoster virus and symptoms include pain and rash in the distribution area supplied by the affected sensory nerves

  • It seems the virus lies dormant in a sensory ganglion and, on becoming activated, migrates down the sensory pathway to the skin

  • An eruption of herpes zoster is more common in elderly people, but may occur at any age and may be related to a delayed hypersensitivity reaction


Herpes zoster 2

Herpes Zoster 2

  • About 10% of all cases affect the ophthalmic division of the trigeminal nerve

  • Involvement of the tip of the nose often indicates that the eye will also be involved, reflecting the distribution of the nasociliary branches

  • This association of ocular involvement with zoster affecting the tip of the nose is called Hutchinson’s sign


Frontal nerve

Frontal Nerve

  • Sensory fibers from the skin and muscles of the forehead and upper eyelid come together and form the supratrochlear nerve, which enters the orbit by piercing the superior medial corner of the orbital septum

  • A second nerve forms in this same general area, the supraorbital nerve, lateral to the supratrochlear nerve

  • The supraorbital nerve enters the orbit as one or two branches: one branch enters through the supraorbital notch, along with the supraorbital artery

  • The supratrochlear and supraorbital nerves combine midway in the obit to form the frontal nerve, which runs back through the orbit between the levator and periorbita, and exits the orbit through the superior orbital fissure above the annulus of Zinn


Cranial nerve innervation of ocular structures

Palpebral nerves


Lacrimal nerve

Lacrimal Nerve

  • Sensory fibers from the lateral part of the upper eyelid and temporal region join and enter the lacrimal gland—they join the sensory fibers that serve the gland itself to form the lacrimal nerve

  • The lacrimal nerve leaves the lacrimal gland and runs posteriorly along the upper border of the lateral rectus muscle

  • The nerve receives a branch from the zygomatic nerve containing the autonomic innervation of the lacrimal gland

  • The lacrimal nerve exits the orbit through the superior orbital fissure above the muscle cone


Cranial nerve innervation of ocular structures

Branch from the zygomatic nerve


Ophthalmic nerve formation

Ophthalmic Nerve Formation

  • After leaving the orbit, the nasociliary nerve, the lacrimal nerve, and the frontal nerve join to form the ophthalmic division of the trigeminal nerve (CN V)

  • The ophthalmic nerve then enters the lateral wall of the cavernous sinus

  • While in the lateral wall, the nerve receives sensory fibers from the oculomotor, trochlear, and abducens nerves

  • Some of these fibers probably carry proprioceptive information from the extraocular muscles


Maxillary division of cn v

Maxillary Division of CN V

  • The maxillary division of the trigeminal nerve forms from the infraorbital and zygomatic nerves, and other nerves from regions around the orbit


Infraorbital nerve

Infraorbital Nerve

  • The infraorbital nerve, formed by sensory fibers from the cheek, upper lip, and lower eyelid, enters the orbit through the infraorbital foramen

  • It runs posteriorly through the infraorbital canal and groove—while it is in the maxillary bone, branches join from the upper teeth and maxillary sinus

  • As the nerve leaves the infraorbital groove it exits the orbit through the inferior orbital fissure and joins other fibers in forming the maxillary nerve


Referred pain

Referred Pain

  • Referred pain is pain felt in an area remote from the actual site of involvement; however, the two areas are usually connected by a sensory nerve network

  • Frequently, the pathways of the trigeminal nerve are involved in referred pain—a common example is the momentary severe bilateral frontal headache sometimes experienced when eating ice cream

  • An abscessed tooth can cause pain described as ocular pain and should be suspected when no orbital cause for pain can be detected

  • These two events likely occur because the overload of sensation carried by the infraorbital nerve is interpreted by the brain as coming from another area also served by the trigeminal nerve


Zygomatic nerve

Zygomatic Nerve

  • Sensory fibers from the lateral aspect of the forehead enter the orbit through a foramen in the zygomatic bone as the zygomaticotemporal nerve

  • Fibers from the lateral aspect of the cheek and lower eyelid enter the orbit through a foramen in the zygomatic bone as the zygomaticofacial nerve

  • These two nerves join to become the zygomatic nerve, which runs along the lateral wall of the orbit, exiting the orbit through the inferior orbital fissure and joining with the maxillary nerve


Maxillary nerve formation

Maxillary Nerve Formation

  • Formed by the joining of the infraorbital nerve, the zygomatic nerve, and nerves from the roof of the mouth, upper teeth, gums, and mucous membranes of the cheek, the maxillary nerve traverses the area between the maxilla and sphenoid bone

  • As it passes near the pterygopalatine fossa, it receives some autonomic fibers from the pterygopalatine ganglion—these fibers are destined for the lacrimal gland (zygomatic n. to lacrimal n.)

  • The maxillary nerve enters the skull through the foramen rotundum


Mandibular division of cn v

Mandibular Division of CN V

  • The mandibular nerve innervates the lower face and contains both sensory and motor fibers

  • It enters the skull via the foramen ovale


Trigeminal nerve formation

Trigeminal Nerve Formation

  • As these three divisions—the ophthalmic, maxillary, and mandibular—enter the skull, they run posteriorly within the lateral wall of the cavernous sinus and enter the trigeminal ganglion (gasserian ganglion, semilunarganglion), where they synapse

  • The ganglion, flattened and semilunar in shape, is located lateral to the internal carotid artery and the posterior part of the cavernous sinus

  • The motor fibers of the mandibular division, which innervate the muscles of mastication, pass along the lower edge of the ganglion—only the sensory fibers synapse within the ganglion


Trigeminal nerve formation ii

Trigeminal Nerve Formation II

  • The fibers then leave the trigeminal ganglion and enter the lateral aspect of the pons as either the sensory root or the motor root of the trigeminal nerve

  • The sensory root carries information from the structures of the face and head, including all orbital structures

  • After entering the brain stem, these fibers form an ascending and descending tract, both terminating in the sensory nuclei of the trigeminal nerve


Trigeminal nerve formation iii

Trigeminal Nerve Formation III

  • The ascending tract terminates in the principal sensory nucleus in the pons, it registers the sensations of touch and pressure

  • The descending tract, which carries pain and temperature sensations, courses through the pons and medulla to the elongated nucleus of the spinal tract

  • The tract extends into the second cervical segment of the spinal cord

  • Information is relayed from the trigeminal nucleus to the thalamus


Oculocardiac reflex

Oculocardiac Reflex

  • The oculocardiac reflex consists of bradycardia (slowed heartbeat), nausea, and faintness and can be elicited by pressure on the globe or stretch of the extraocular muscles (e.g., during surgery)

  • Fibers from the trigeminal spinal nucleus project into the reticular formation near the vagus nerve nuclei and can activate vagus synapses, precipitating this reflex

  • The motor aspect of the reflex can be blocked by a retrobulbar anesthesia or intravenous or intramuscular atropine


Efferent pathway motor nerves

Efferent Pathway: Motor Nerves

  • The cranial nerves that supply striated muscles of the orbit and adnexa are the:

    • Oculomotor nerve

    • Trochlear nerve

    • Abducens nerve

    • Facial nerve


Oculomotor nerve cranial nerve iii

Oculomotor Nerve: Cranial Nerve III

  • The oculomotor nerve innervates the superior rectus, medial rectus, inferior rectus, inferior oblique, and the superior palpebral levator muscles

  • It also provides a route along which the autonomic fibers travel to innervate the iris sphincter muscle, the ciliary muscle, and the smooth muscles of the eyelid


Oculomotor nucleus

Oculomotor Nucleus

  • The oculomotor nucleus is located in the midbrain, ventral to the cerebral aqueduct, at the level of the superior colliculus

  • It extends in a column from the posterior edge of the floor of the third ventricle to the trochlear nucleus

  • A defined area or subnucleus within the oculomotor nucleus controls each muscle—the proposed areas are based primarily on animal models

  • The nuclei for the MR, IR, IO, and SR are located in both the left and right oculomotor nucleus—the nucleus for the levator is single and is located centrally in the caudal area

  • Fibers to the IR, IO, and MR supply the ipsilateral eye—fibers innervating the SR decussate and supply the contralateral eye


Oculomotor nucleus ii

Oculomotor Nucleus II

  • The decussating fibers pass through the opposite superior rectus nucleus—so damage to the right oculomotor nucleus might result in bilateral SR involvement

  • The centrally placed caudal nucleus provides innervation for both levator muscles

  • An autonomic nucleus, the accessory third nerve nucleus, or Edinger-Westphal nucleus, supplies parasympathetic innervation to the ciliary and iris sphincter muscles—it is located in the rostral, ventral part of the oculomotor nucleus


Oculomotor nerve pathway

Oculomotor Nerve Pathway

  • Fibers from each of the individual nuclei join, forming the fascicular part of the nerve that passes through the red nucleus and the cerebral peduncle

  • These fibers emerge from the interpeduncular fossa on the anterior aspect of the midbrain as the oculomotornerve

  • The nerve passes between the superior cerebellar and posterior cerebral arteries as it runs forward, lateral to, and slightly inferior to the posterior communicating artery of the circle of Willis

  • The nerve pierces the roof of the cavernous sinus and runs within its lateral wall above the trochlear nerve

  • While in the cavernous sinus the oculomotor nerve sends small sensory branches to the ophthalmic nerve and receives sympathetic fibers from the plexus around the internal carotid


Oculomotor nerve pathway ii

Oculomotor Nerve Pathway II

  • The oculomotor nerve exits the sinus and enters the orbit through the superior orbital fissure, having divided into superior and inferior divisions—both divisions are within the oculomotor foramen

  • The superior branch runs medially above the optic nerve and enters the superior rectus on its inferior surface—additional fibers either pierce the muscle or pass around it to innervate the levator

  • The inferior branch runs below the optic nerve and divides into three branches


Oculomotor nerve pathway iii

Oculomotor Nerve Pathway III

  • The first branch enters the MR on its lateral surface

  • The second branch enters the IR on its upper surface

  • The third branch gives off parasympathetic fibers that form the parasympathetic root to the ciliary ganglion—then it runs along the lateral border of the IR, crossing it to enter the IO muscle near its midpoint

  • These parasympathetic fibers arise in the Edinger-Westphal nucleus and synapse in the ciliary ganglion


Trochlear nerve cranial nerve iv

Trochlear Nerve: Cranial Nerve IV

  • The trochlear nerve innervates the SO muscle

  • Its fibers travel dorsally and decussate

  • CN IV is the only cranial nerve to cross—so the trochlear nucleus innervates the contralateral SO muscle

  • The trochlear nucleus is located in the midbrain anterior to the cerebral aqueduct and below the oculomotor nucleus, at the level of the inferior colliculus


Trochlear nerve pathway

Trochlear Nerve Pathway

  • The trochlear nerve is the only one that leaves the dorsal aspect of the brain

  • It is the most slender of the cranial nerves and its attachment is very delicate

  • The nerve’s small diameter is a consequence of its serving only one muscle and the most slender muscle at that

  • As the trochlear nerve emerges from the dorsal midbrain below the inferior colliculus, it decussates and curves around the cerebral peduncle at the upper border of the pons, paralleling the superior cerebellar and posterior cerebral arteries

  • It passes between these two vessels and runs forward lateral to the oculomotor nerve


Trochlear nerve pathway ii

Trochlear Nerve Pathway II

  • The trochlear nerve enters the wall of the cavernous sinus and lies between the oculomotor nerve and the ophthalmic division of the trigeminal nerve

  • While in the sinus the trochlear nerve sends sensory fibers to the ophthalmic nerve

  • It enters the orbit through the superior orbital fissure above the common tendinous ring, outside the muscle cone

  • The trochlear nerve runs with the frontal nerve to the medial side of the orbit above the levator and superior rectus muscles and enters the upper surface of the superior oblique muscle


Abducens nerve cn vi

Abducens Nerve: CN VI

  • The abducens nerve innervates the lateral rectus muscle

  • The abducens nucleus is located near the midline of the pons alongside the floor of the fourth ventricle

  • The fibers from the nucleus pass through the pons and exit in the groove between the pons and the medulla oblongata

  • The abducens nucleus also contains internuclear neurons that communicate with the nucleus for the contralateral medial rectus in the oculomotor complex via the medial longitudinal fasiculus—this is the pathway for conjugate horizontal eye movements


Abducens nerve ii

Abducens Nerve II

  • This pathway receives information from higher CNS centers, including the paramedial pontine reticular formation, the cerebellum, and the vestibular nucleus

  • Thus, coordinated movement of the ipsilateral lateral rectus and the contralateral medial rectus results in conjugate horizontal eye movements


Abducens nerve pathway

Abducens Nerve Pathway

  • In its long tortuous course, the abducens nerve runs along the occipital bone at the base of the skull and up along the posterior slope of the petrous portion of the temporal bone, making a sharp bend over the petrous ridge and entering the cavernous sinus

  • Within the sinus it lies near the lateral wall of the internal carotid artery—it gives off small branches, possibly proprioceptive fibers, to the ophthalmic nerve

  • The abducens nerve enters the orbit through the superior orbital fissure within the common tendinous ring and innervates the lateral rectus on the medial surface


Superior orbital fissure

Superior Orbital Fissure

  • The trochlear, frontal, and lacrimal nerves and the superior ophthalmic vein are located in the superior orbital fissure above the muscle cone

  • The superior and inferior divisions of the oculomotor nerve, the abducens nerve, and the nasociliary nerve are located within the superior orbital fissure and the common tendinous ring

  • The inferior ophthalmic vein lies below the fissure and the tendinous ring


Control of eye movements

Control of Eye Movements

  • Communication between areas of the CNS is necessary to produce controlled, coordinated eye movements

  • The corticonuclear tract contains fibers that run from the cerebral hemispheres to the nuclei of CNs III, IV, and VI—the tectobulbar tract connects the superior colliculus to the CN III, IV, and VI nuclei

  • The medial longitudinal fasiculus extends from the midbrain into the spinal cord and connects the vestibular nucleus, the oculomotor nucleus, the abducens nucleus, and the trochlear nucleus, providing a connection between the motor nuclei (eye movement control) and the vestibular apparatus


Facial nerve cn vii

Facial Nerve: CN VII

  • The facial nerve has two roots—the large motor root innervates the facial muscles, and the smaller root contains sensory and parasympathetic fibers

  • The sensory fibers carry taste sensations from the tongue

  • The parasympathetic nerves supply secretomotor fibers to the various glands of the face, including the lacrimal gland

  • The motor nucleus of the facial nerve is located in the reticular formation of the pons

  • The upper segment of the nucleus supplies the frontalis, procerus, corrugator superciliaris, and orbicularis muscles, and the lower segment supplies the remaining facial muscles


Facial nerve pathway

Facial Nerve Pathway

  • The fibers leave the facial nucleus and arch around the abducens nucleus and emerge as the facial nerve from the brain stem at the lower border of the pons

  • The facial nerve enters the internal acoustic foramen in the petrous protion of the temporal bone and runs through a canal in the bone

  • While in the temporal bone, parasympathetic fibers en route to the lacrimal gland are given off as the greater petrosal nerve

  • The motor fibers of the facial nerve emerge through the stylomastoid foramen, pass below the external auditory canal, travel over the mandibular ramus, and divide into several branches

  • The upper two—the temporal and zygomatic branches—supply the frontalis, procerus, corrugator, and orbicularis muscles


Cranial nerve damage

Cranial Nerve Damage

  • Injury to a sensory cranial nerve results in anesthesia, a loss of sensation in the innervated area

  • Injury to a cranial motor nerve causes either a partial loss (paresis) or a total loss (paralysis) of muscle function

  • Paresis or paralysis of an extraocular muscle can result in diplopia if the involvement is acquired—in congenital involvement, diplopia usually is not present, because the brain has learned to disregard the double image through the mechanism of suppression, which can lead to amblyopia

  • Nerve fibers can be damaged by a compromised blood supply caused by vascular disease (e.g., hypertension, atherosclerosis, diabetes mellitus) or by space-occupying lesions (e.g., aneurysms, hemorrhages, tumors) that exert pressure on the nerve fibers


Cranial nerve damage ii

Cranial Nerve Damage II

  • In various studies of isolated extraocular nerve paralysis, the sixth cranial nerve was reported to be affected most often, and the fourth cranial nerve was affected least often

  • The tortuosity and length of the abducens nerve, (CN VI), make it susceptible to compression and stretching injuries and may explain why is damaged so frequently

  • A number of clinical signs and symptoms accompany damage to the motor nerves that innervate the extraocular muscles

  • Muscle paresis or paralysis will be evident in testing ocular motility (diagnostic H test)

  • In acquired extraocular muscle impairment, a patient often attempts to minimize diplopia by positioning the head in a compensatory position


Cranial nerve damage iii

Cranial Nerve Damage III

  • If a horizontal deviation is present, the head will be turned to the right or left

  • With a vertical deviation the head is raised or lowered, and if a torsional deviation occurs the head is tilted toward the shoulder

  • With right superior oblique involvement the head will be turned to the left, positioned down, and tilted toward the left shoulder

  • Why is this so?


Rso compensation

RSO Compensation

  • When the RSO is impaired, the RIO is unopposed, so the eye is extorted, abducted, and elevated

  • The head adjustment is to tilt the head toward the left shoulder to compensate for the extorsion, turn the head to the left to compensate for the abduction, and tilt the head down to compensate for the elevation


Oculomotor damage midbrain involvement

Oculomotor Damage: Midbrain Involvement

  • A midbrain lesion can effect the entire oculomotor nucleus or may selectively effect only some subnuclei—however, such selective damage is rare

  • If the lesion effects the entire nucleus, the muscles involved are the ipsilateral medial rectus, inferior rectus, and inferior oblique, contralateral superior rectus, and both levators

  • The ipsilateral superior rectus might also be involved, because the decussating fibers pass through the contralateral superior rectus nucleus


Oculomotor damage midbrain involvement ii

Oculomotor Damage: Midbrain Involvement II

  • The trochlear nucleus is near the oculomotor nucleus, and if it too is involved, the contralateral superior oblique muscle will be affected

  • The clinical presentation (complete oculomotor, ipsilateral SR, and contralateral SO involvement) would show the ipsilateral eye positioned out in primary position and only able to move in as far as the midline—the contralateral eye would be unable to elevate in abduction and unable to depress in adduction


Oculomotor damage intracranial involvement

Oculomotor Damage: Intracranial Involvement

  • The oculomotor nerve lies near several blood vessels in its intracranial path and frequently is affected by an aneurysm of the posterior communicating artery

  • An aneurysm of the superior cerebellar artery or the posterior cerebral artery could also impinge on the nerve, damaging fibers

  • Once the oculomotor nerve exits the midbrain, all its fibers supply the ipsilateral eye, and the dysfunction is unilateral

  • Damage to the nerve results in ptosis because of levator nerve paralysis—in primary position the eye is positioned out because of the unopposed action of the superior oblique and lateral rectus muscles (due to the SO being unaffected, the eye should also be positioned down, but this is not always seen)


Oculomotor damage intracranial involvement ii

Oculomotor Damage: Intracranial Involvement II

  • The eye cannot adduct and, in the abducted position, cannot move up or down

  • In paralysis of the iris sphincter and ciliary muscle, the pupil will be dilated, and accommodation will not occur

  • Incomplete lesions of the oculomotor nerve are possible—in external ophthalmoplegia the extraocular muscles are paralyzed and the intrinsic muscles are spared; in internal ophthalmoplegia the internal muscles are paralyzed and the extraocular muscles are spared


Oculomotor damage intracranial involvement iii

Oculomotor Damage: Intracranial Involvement III

  • As the oculomotor nerve exits the midbrain, the parasympathetic fibers are superficial, and as the nerve nears the orbit, the parasympathetic fibers move into the center of the nerve and are better protected

  • Sparing of the parasympathetic fibers in ischemic lesions may account for normal pupillary reflexes usually seen with diabetic ophthalmoplegia


Oculomotor damage cavernous sinus involvement

Oculomotor Damage: Cavernous Sinus Involvement

  • The lateral wall of the cavernous sinus contains the oculomotor nerve as well as the trochlear, ophthalmic, and maxillary nerves

  • A lesion that effects all these nerve would leave only the lateral rectus muscle still functioning

  • The eye would be positioned out in primary gaze and could only move from the lateral position to the midline

  • Anesthesia of the facial areas served by the ophthalmic and maxillary nerves would be present in addition to the impaired ocular motility


Oculomotor damage orbital involvement

Oculomotor Damage: Orbital Involvement

  • Both divisions of the oculomotor nerve are located within the muscle cone, together with the abducens and nasociliary nerves

  • A retrobulbar tumor or inflammation involving these nerves would leave only the superior oblique muscle functional

  • In primary position the eye would be positioned downward and outward slightly and would be fairly immobile

  • Corneal sensitivity could be decreased because of nasociliary nerve involvment


Aberrant regeneration of the oculomotor nerve

Aberrant Regeneration of the Oculomotor Nerve

  • After injury the brain may attempt to repair a nerve, and some attempts may be misdirected, resulting in an unusual clinical presentation

  • Fibers going to the inferior oblique may sprout branches that also innervate the sphincter, causing pupillary constriction on elevation

  • Fibers innervating the medial rectus may send sprouts that innervate the sphincter, causing miosis with adduction or convergence


Trochlear damage

Trochlear Damage

  • When the superior oblique muscle is affected by trochlear nerve damage, the eye is elevated in primary gaze and is unable to move down in the adducted position

  • The head may be tilted toward the opposite shoulder to compensate for the unopposed extortion of the inferior oblique muscle

  • Under the age of 10 years, palsies involving the trochlear nerve are usually congenital, and between 21 and 40 years of age the usual cause is trauma—otherwise the palsy may be idiopathic (i.e. arising spontaneously from an unknown cause)


Trochlear damage midbrain involvement

Trochlear Damage: Midbrain Involvement

  • Damage to the trochlear nucleus will affect the contralateral superior oblique

  • Because of its closeness to the oculomotor nucleus, a lesion could affect both cranial nerve nuclei, resulting in the clinical presentation described earlier


Trochlear damage intracranial involvement

Trochlear Damage: Intracranial Involvement

  • The trochlear nerve follows almost the same path as the oculomotor nerve and is susceptible to the same injuries

  • Damage to the trochlear nerve affects the ipsilateral superior oblique muscle, causing the eye to be elevated in primary gaze and unable to move down in the adducted position


Trochlear damage cavernous sinus involvement

Trochlear Damage: Cavernous Sinus Involvement

  • A lesion in the lateral wall of the cavernous sinus could affect the trochlear nerve

  • It could also affect the oculomotor, ophthalmic, and maxillary nerves, causing the clinical presentation described earlier


Trochlear damage orbital involvement

Trochlear Damage: Orbital Involvement

  • The trochlear nerve lies above the muscle cone, near the frontal nerve, and injury affecting both nerves could impair the SO muscle, limiting depression in the adducted position

  • Decreased sensitivity of the areas of the skin and scalp innervated by the branches of the frontal nerve might also be present


Abducens damage cn vi

Abducens Damage: CN VI

  • Damage to the abducens nerve results in paralysis of the lateral rectus muscle—because of the unopposed action of the medial rectus muscle, a convergent strabismus is evident (that is, the affected eye is adducted)

  • The eye will be unable to abduct, but adduction will be normal

  • The patient may try to compensate for the diplopia by turning the face toward the paralyzed side, centering the usable range of muscle contraction


Abducens damage pons involvement

Abducens Damage: Pons Involvement

  • Both the abducens and facial nuclei are located in the pons, and the fasciculus of the facial nucleus arches around the abducens nucleus

  • Damage here could affect the lateral rectus and the muscles of the forehead and orbicularis

  • Symptoms might include inability to abduct the eye and lagophthalmos, the inability to bring the eyelids together in attempted closure

  • The abducens nucleus also contains internuclear neurons, so the patient may have a restriction when attempting to turn both eyes toward the side of the lesion

  • The contralateral medial rectus muscle may not be activated in this lateral gaze, but the patient will be able to converge


Abducens damage intracranial involvement

Abducens Damage: Intracranial Involvement

  • The course of the abducens nerve makes it particularly susceptible to increased intracranial pressure, which causes the brain stem to be displaced posteriorly, stretching the nerve over the bony ridge of the petrous portion of the temporal bone

  • Fractures of the base of the skull and aneurysms of the basilar and carotid arteries can affect the abducens nerve


Abducens damage cavernous sinus involvement

Abducens Damage: Cavernous Sinus Involvement

  • The abducens nerve is located near the internal carotid artery within the cavernous sinus

  • Often it is the first nerve affected with an aneurysm of this vessel

  • A lateral rectus palsy with Horner’s syndrome (ptosis, miosis, and facial anhydrosis) on the same side, suggesting sympathetic involvement, is indicative of cavernous sinus and internal carotid artery involvement


Abducens damage orbital involvement

Abducens Damage: Orbital Involvement

  • The abducens nerve is located within the muscle cone

  • It accompanies the two divisions of the oculomotor nerve and the nasociliary nerve (with the clinical presentation described earlier)


The end

The End


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