This document summarizes the anatomy and function of the trochlear and abducent nerves. It describes that the trochlear nerve is entirely motor and supplies the superior oblique muscle. It has a long course as it arises from the midbrain, crosses to the other side, and enters the orbit. The abducent nerve is also motor and supplies the lateral rectus muscle. Its nucleus is located in the pons and it innervates the lateral rectus to control eye movement. Clinical features of palsies of each nerve are provided such as diplopia and limitations in eye movement.

1. Anatomy of
Trochlear and Abducent Nerve
Dr. Akshat Tyagi
Dept of Ophthalmology SMC, Meerut

2. TROCHLEAR NERVE
•The trochlear nerve is entirely motor in function
and supplies only SO.
•It differ from other Cranial Nerves :
-arises from dorsal aspect of midbrain
-crosses completely to other side
-longest and thinnest

3. FUNCTIONAL COMPONENTS
•Somatic Efferent
•General Somatic Afferent

4. NUCLEUS
•Situated in ventromedial part of central grey
matter of midbrain at level of inferior
colliculus.
•It is caudal to and continuous with the third
nerve nucleus complex.

6. CONNECTIONS OF THE NUCLEUS
CEREBRAL CORTEX
 Motor cortex – of both sides through the corticonuclear tracts
Visual cortex – through the superior colliculus and tactobulbar tracts
Frontal eye fields
SUPERIOR COLLICULUS
Through the descending pre dorsal bundles

7. NUCLEI OF THIRD, SIXTH, EIGHTH CRANIAL NERVE
through the medial longitudinal bundle
CEREBELLUM – Through the vestibular nuclei
VISUAL AND TORSIONAL GAZE CENTRES

8. COURSE AND DISTRIBUTION
It has 4 parts:
Fasicular part
Pre-cavernous part
Intracavernous part
Intraorbital part

9. FASICULAR PART
Fasciculus consist of efferent
fibres
leave the nucleus
Pass posteriorly around the
aqueduct in central grey
matter
Decussate completely in
anterior medullary velum.

10. PRECAVERNOUS PART
Emerge from superior medullary velum just
below inferior colliculus.
Winds around superior cerebellar peduncle and
cerebral peduncle above pons.
Runs beneath the free edge of tentorium, passes
b/w posterior cerebral and superior cerebellar
arteries.

12. Appears ventrally lateral to cerebral peduncle
Pierces dura on posterior corner of roof of
cavernous sinus to enter it.

13. INTRACAVERNOUS PART
In sinus it lies below 3rd
and above 1st division of
5th nerve
In anterior part of sinus
crosses over the third
nerve and leaves the sinus
Pass through lateral part
of superior orbital fissure

14. INTRAORBITAL PART
Enter the orbit through
lateral part of superior
orbital fissure
Pass medially above the
origin of LPS
ends by supplying the
SO

15. CAUSES OF NUCLEAR AND FASCICULAR
FOURTH CRANIAL NERVE PALSIES
• Congenital(40%)
• Trauma – causes B/L nerve palsy due to impact
on the anterior medullary velum
• Idiopathic (20%)
• Vascular and neurological causes
• Aneurysms and tumors – rare causes

16. CLINICALLY APPLIED ASPECTS
1. Hyperdeviation: due to weakness of SO,
becomes more obvious by head tilt towards
the ipsilateral shoulder
(BIELSCHOWSKY’S head tilt test)
2. Ocular movements: depression is limited in
adduction.
3. Diplopia: homonymous vertical diplopia occur
in down gaze

17. 4. Abnormal head posture:
to avoid diplopia head takes a posture :
-face turned to opposite side,
-chin depressed and
-head tilted towards the opposite shoulder.

18. PARK’S THREE STEP TEST
• This clinical test allows isolation of a single weak muscle in patients
with vertical diplopia of acute onset.
• Step one. In the primary position, the hypertropic eye is identified,
narrowing the affected muscle to one of the depressors of the
hypertropic eye (superior oblique or inferior rectus) or one of the
elevators of the hypotropic eye (superior rectus or inferior oblique).
In a fourth nerve palsy, the involved eye is higher.

19. • Step two. The eyes are examined in right and left gaze to determine
where the hypertropia is greater, thus assigning the weakness to the
two of the four previously identified muscles having the greatest
vertical action in that position. In superior oblique weakness the
deviation is worse on opposite gaze – WOOG.

20. • Step three
• The Bielschowsky head tilt test (BHTT) is performed with the patient
fixating on a target directly ahead, optimally at 3 metres.
• The head is tilted to each side in turn in order to assess the muscles
responsible for cyclotorsion, with observation to determine the
position in which the hypertropia is worse. On tilt to one side, the
superior oblique and superior rectus (note that both are superior)
muscles of the eye of that same side correctively intort and the
inferior rectus and inferior oblique (note both are inferior) of the
contralateral eye correctively extort. From the two muscles
previously isolated, one can be eliminated.

21. • In fourth nerve palsy the deviation is better on opposite tilt – BOOT
In practice, as the three-step test is almost always employed to
confirm a fourth nerve palsy, the BHTT alone is often sufficient for a
working diagnosis.

23. Abducent nerve
•Sixth cranial nerve
•Motor in function
•Supplies the Lateral rectus muscle

24. FUNCTIONAL COMPONENTS
•SOMATIC EFFERENT – supplies the lateral rectus
muscle hence involved in the movement of the eyeball
•GENERAL SOMATIC AFFERENT – Carries proprioceptive
impulses from the lateral rectus muscle which reach
the mesencephalic nucleus of the trigeminal nerve

25. NUCLEUS
•Situated in lower part of pons, close to
midline, beneath the floor of 4th ventricle
•Close to fasciculus of facial nerve.
•Two type of multipolar cells: large and small.

27. CONNECTIONS OF THE NUCLEUS
CEREBRAL CORTEX
Motor cortex - through corticonuclear fibres
Visual cortex – through superior colliculus and tactobulbar tract
Frontal eye fields
NUCLEI OF THIRD, FOURTH, EIGHTH CN - Through medial longitudinal
bundle
PRETECTAL NUCLEUS - Through tectobulbar tract

28. CEREBELLUM – Through the vestibular nuclei
HORIZONTAL GAZE CENTRE – (paramedian pontine
reticular formation)-Through the medial longitudinal
bundle

29. COURSE AND DISTRIBUTION
4 parts:
Fascicular part
Basilar part
Intracavernous part
Intraorbital part

30. FASCICULAR PART
Has efferent fibres which start
From nucleus
Pass forward traversing the
medial leminiscus and pyramidal
tract.
Emerge by seven to eight rootlets
from junction of pons and
medulla , lateral to pyramidal
prominence.

31. BASILAR PART
Runs forward, upwards and slightly laterally through cisterna pontis
between the pons and occipital bone.
Runs on back of petrous temporal bone near apex, at its upper border
nerve bends forward at 90 degree
Enters the cavernous sinus through its posterior wall at a point lateral to
the dorsum sellae and superior to the apex of petrous temporal bone

32. INTRACAVERNOUS PART
In cavernous sinus nerve runs almost horizontally forward, lie below and
lateral to ICA.
Enters the orbit through middle part of superior orbital fissure within the
annulus of Zinn
In superior orbital fissure, the nerve lies inferolateral to oculomotor and
nasociliary nerves.

33. INTRAORBITAL PART
• In orbit, nerve runs
forwards and enters the
ocular surface of LR
after dividing into 3 to 4
branches.

34. CLINICALLY APPLIED ASCEPTS
FEATURES:
1. Deviation: eyeball is converged due to unopposed action of MR .
2. Ocular movements: abduction is limited due to LR weakness.
3. Diplopia: uncrossed horizontal diplopia become worse on side of
paralysis.
4. Head posture: face turned towards the side of paralysed muscle to
minimize diplopia.

36. FEATURES OF 6TH NERVE PALSY
1. Supranuclear lesions:
Cause loss of conjugate movements of eyeball.
2. Nuclear lesions
• Never causes isolated 6th nerve palsy
• Ipsilateral 6th nerve palsy
• Ipsilateral 7th nerve palsy of UMN due to
involvement of facial colliculus.

37. •Loss of conjugate movements on same side due to
involvement of horizontal gaze centre in the pontine
paramedian reticular formation (PPRF)

38. 3.FASCICULAR LESIONS
Foville’s syndrome - lesion of dorsal pons involving
6th nerve fasciculus as it passes through
PPRF(paramedian pontine reticular formation) has
following characteristics:
•Ipsilateral 6th nerve palsy
•Loss of conjugate movement on same side
•Ipsilateral facial nerve palsy
•Facial analgesia (sensory portion of 5th nerve)
•Deafness

39. Millard-Gubler syndrome:
due lesion in ventral pons involving fasciculus
•Ipsilateral 6th nerve palsy
•Contralateral hemiplegia

40. 4. Lesions in basilar part:
Causes:
Acoustic neuroma
Nasopharyngeal tumors
Fracture of base of skull
1st sign in acoustic neuroma – diminished corneal sensation & 1st symptom
is hearing loss.

41. Gradenigo syndrome:
(involvement of petrous bone from otitis media)
•Ipsilateral 6th nerve palsy
•Deafness
•Neuralgia in the distribution of first division of
trigeminal nerve
•Facial weakness

42. In cases of raised ICP:
•In raised ICT, the brainstem is shifted downwards
towards foramen magnum so the susceptibility of
damage to 6th nerve increases due to its long course
and sharp bend over superior border of petrous
temporal bone.
•LR Palsy is a false localising sign in this case.

44. Lesions of intracavernous part:
CAUSES:
•Diabetes
•Hypertension
•Aneurysms
•Meningioma
•Carotid cavernous fistulae
•Tolosa-hunt syndrome

45. LESIONS IN INRAORBITAL PART:
•orbital apex syndrome
•Superior orbital fissure syndrome

46. Thank You