Neuro Ophthalmology

1. Abducens Nerve
13th August 2020
DR M SAQUIB
Vice Principal
MBBS,MS , FSCEH DELHI,FHVDESAI PUNE,
EX REGISTRARA JNMCH,AMU
CONSULTANT OPHTHALMOLOGIST
HOD D/O OPHTHALMOLOGY
G.S .MEDICAL COLLEGE
Founder sec: MEDICS India ,
Mail-dms2k5@gmail.com , 9634123800

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The abducens nerve is the sixth paired cranial
nerve. It has a purely somatic motor function –
providing innervation to the lateral rectus
muscle.

3. Anatomical Course
▸ The abducens nerve arises from the abducens nucleus in
the pons of the brainstem.
▸ It exits the brainstem at the junction of the pons and the
medulla.
▸ It then enters the subarachnoid space and pierces the dura
mater to travel in an area known as Dorello’s canal.
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4. At the tip of petrous temporal bone, the abducens nerve
leaves Dorello’s canal and enters the cavernous sinus (a
dural venous sinus). It travels through the cavernous sinus
and enters the bony orbit via the superior orbital fissure.
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5. Motor Function
▸ The abducens nerve provides innervation to
the lateral rectus muscle – one of
the extraocular muscles.
▸ The lateral rectus originates from the lateral part
of the common tendinous ring, and attaches to
the anterolateral aspect of the sclera.
▸ It acts to abduct the eyeball (i.e. to rotate the
gaze away from the midline).
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10. ▸ Clinical Relevance
▸ The abducens nerve is examined in
conjunction with the oculomotor and
trochlear nerves by testing the movements of
the eye.
▸ The patient is asked to follow a point with
their eyes (commonly the tip of a pen)
without moving their head.
▸ The target is moved in an ‘H-shape’ and the
patient is asked to report any blurring of
vision or diplopia (double vision).
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13. Clinical Relevance - Abducens Nerve Palsy
▸ Can be caused by any structural pathology
which leads to downwards pressure on the
brainstem (e.g. space-occupying lesion).
▸ This can stretch the nerve from its origin at
the junction of the pons and medulla.
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14. Clinical features
▸ Abducens nerve palsy include diplopia,
the affected eye resting in adduction
(due to unopposed activity of the medial
rectus), and inability to abduct the eye.
▸ The patient may attempt to compensate
by rotating their head to allow the eye to
look sideways
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15. ▸ The sixth cranial nerve is the most frequent
cause of an isolated ocular motor palsy; it
typically presents as horizontal diplopia
that worsens on ipsilateral gaze, especially
viewing at distance.
▸ The abduction deficit is typically
associated with an Esodeviation that
increases with gaze to the affected side .
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16. Risk Factors
▸ Inflammatory and microvascular conditions are risk factors
for abducens nerve palsy. Other risk factors include
▸ multiple sclerosis,
▸ encephalitis,
▸ meningitis,
▸ cavernous sinus thrombosis, hypertension,
hypercholesterolemia,
▸ aneurysm,
▸ diabetes,
▸ arteriosclerosis,
▸ birth trauma, and neurosurgical intervention.[18]
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18. ▸ Lesions of the cerebellopontine
angle (especially acoustic neuroma or
meningioma) may involve the sixth and other
contiguous cranial nerves, causing decreased
facial and corneal sensitivity (CN V), facial
paralysis (CN VII), and decreased hearing
with vestibular signs (CN VIII).
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19. ▸ Chronic inflammation of the petrous
bone may cause an ipsilateral abducens
palsy and facial pain (Gradenigo
syndrome), especially in children who
have experienced recurrent infections
of the middle ear.
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20. ▸ After Exiting The Pre–pontine Space, The
Sixth Nerve Is Vulnerable To Meningeal Or
Skull-based Processes, Such As
▸ Meningioma,
▸ Nasopharyngeal Carcinoma,
▸ Chordoma, Or Chondrosarcoma
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21. ▸ In addition, the sixth nerve is
susceptible to injury from shear forces of
head trauma or elevated intracranial
pressure. In such cases, injury occurs
where the sixth nerve enters the
cavernous sinus through the Dorello
canal (the opening below the
petroclinoid ligament).
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22. ▸ Congenital sixth nerve palsies almost
never occur in isolation.
▸ Abduction paresis present early in life
usually manifests as a Duane syndrome
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23. ▸ Isolated sixth nerve palsies in
adults over the age of 50 are
usually ischemic; ocular motility in
these cases always improves and
typically resolves within 3 months.
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24. ▸ In general, at the onset of an isolated
sixth nerve palsy in a vasculopathic
patient, neuroimaging is not required.
▸ As noted with other isolated ocular motor
cranial nerve palsies, medical evaluation
is appropriate.
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25. ▸ However, a cranial MRI is mandatory if obvious
improvement has not occurred after 3 months.
▸ Other diagnostic studies that may be required
include lumbar puncture,
▸ chest imaging, and
▸ hematologic studies to identify an underlying
systemic process such as collagen vascular
disease,
▸ , or syphilis
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26. ▸ Impaired abduction in patients under age 50
requires careful scrutiny, because few such
cases are due to ischemic cranial neuropathy.
▸ Younger individuals should undergo
appropriate neuroimaging.
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27. ▸ If negative, consideration should be given
to neuromuscular junction disease, by
obtaining acetylcholine antibodies or
performing Tensilon testing; mechanical
pathophysiologies, such as thyroid eye
disease with medial rectus involvement;
and meningeal-based disease, by
obtaining a lumbar puncture.
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28. ▸ Leukemia or brainstem glioma are
important considerations in children.
▸ In adolescents and young adults,
demyelination may be the cause.
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