4TH NERVE PALSY
TROCHLEAR NERVE PALSY
SUPERIOR OBLIQUE PALSY
Thinnest and longest 75mm.
Only CN that comes out from the dorsal aspect of the brainstem.
Only CN that crosses completely to the opposite side. Thus
originates from the contralateral nucleus.
Somatic motor component , innervates the superior oblique of the
Nucleus lies at the level of the
• From each nucleus, the nerve
fibres run laterally and emerge
from the dorsal aspect of the
• Pass medially and decussate (X)
• Thus it crosses completely before
• Once the 4th CN exits from the
brain from the dorsal side it turns
ventral and passes the Posterior
Cerebral Artery and Superior
• Then it pierces the arachnoid and
enters the subdural space on the
posterior corner of the roof of the
ANATOMY - CONT
• In the cavernous sinus it
runs on the lateral wall
below the Oculomotor nerve
and above the 1st div of 5th
• Before crossing the
cavernous sinus it crosses
the 3rd nerve through the
lateral part to enter the
superior orbital fissure
Anatomy of the 4th cranial nerve
ANATOMY - CONT
• In the intraorbital part, the 4th CN
doesn’t transverse through the
annulus of zinn, it projects anteriorly,
superiorly and medially to it
• Travels temporal and inferior to
innervate the superior oblique
4TH CN PALSY – CASE HISTORY
Initial observations: 1. Head tilt on the affected side
2. Hypertropia-affected side
3. Facial asymmetry
General health: DM / HTN / Myasthenia gravis / IC tumours / TRAUMA
Family history: Congential 4th CN palsy , Autosomal dominant form
Ocular history: Tx for diplopia, head posture in childhood.
Questions to ask further as a basis for investigation:
Diplopia? Vertical / horizontal ? Any torsion ? Duration ? Constant or
intermittent ? Worsen on reading or climbing stairs ? Neck pain ?
CAUSES OF AN ISOLATED 4TH NERVE PALSY
I)CONGENITAL : Congenital lesions are a common cause ,
although symptoms do not develop until decompensation occurs in adult
life. Children develop a compensatory head tilt in order to compensate for
underacting superior oblique muscle, on the contralateral side.
II) ACQUIRED :
1.TRAUMA : trauma is an important cause of 4th nerve palsy accounting for
30% of accquired 4th nerve palsies, 4 th nerve is the most commonly
involved nerve in a traumatic palsy.
Trauma usually causes bilateral 4th nerve palsies due to an impact in the
area of the Anterior medullary vellum, where the two nerves decusate.
2.IDIOPATHIC : in about 20% of cases the cause is unknown.
3.VASCULAR AND NEUROLOGICAL : These account for about 5 % of trochlear nerve
palsies , in older individuals microvasculopathy secondary to diabetes
atherosclerosis or hypertension may cause an isolated 4th nerve palsy.
Aneurysms and tumors are rare causes.
Thyroid related orbitopathy and Myasthenia gravis may mimic as an
isolated 4th nerve palsy due to fibrotic inferior oblique , superior rectus.
SYNDROMES OF 4TH CN PALSY
Most often due to stroke, less often neoplasm, and almost never isolated; other
causes include demyelinative disease and trauma.
Rare, same associations as nuclear; may get contralateral Horner’s syndrome;
trauma (especially near anterior medullary velum) may cause bilateral CN IV palsies.
Usually due to closed head
trauma; rarely tumor, infection or
Due to cavernous sinus disease
from inflammation (sarcoidosis),
infection (fungal), or neoplasm
associated with CN III, V, and VI
findings and sympathetic
Trauma, inflammatory or
FEATURES OF 4TH NERVE PALSY
The features of nuclear , fasicular and peripheral 4th nerve palsies are
clinically identical except that nuclear lesions produce CONTRALATERAL
superior oblique weakness.
DIPLOPIA : Acute onset of a vertical diplopia, which is more on
downward gaze ,it is noted by patients while coming down stairs and
while doing near work.
1)HYPERTROPIA – the involved eye is higher as a result of weakness of
the superior oblique muscle, which becomes more prominent when the
head is tilted towards the ipsilateral shoulder
2)RESTRICTED OCULAR MOVEMENTS: there is limitation of
depression on adduction.
3)ABNORMAL HEAD POSTURE: to avoid diplopia ,head takes a posture
towards the action of the superior oblique muscle, face is slightly turned to
the opposite side, chin is depressed, and head is tilted towards the
COMPENSATORY HEAD POSTURE IN
LEFT 4TH NERVE PALSY
HEAD IS TILTED TO THE RIGHT.
FACE IS TURNED TO THE RIGHT.AND
CHIN IS DEPRESSED.
SPECIAL TESTS USED IN DIAGNOSIS OF
4TH NERVE PALSY :
1) PARKS –BIELSCHOWSKY THREE STEP TEST.
2) DOUBLE MADDOX ROD TEST.
Park-Bielschowsky 3 step test
STEP 1 :( to assess which eye is hypertropic in the primary gaze.)
In case of left hypertropia, the following four muscles
could be involved:
1) Depressors of the left eye i.e superior oblique and
2) Elevators of the right eye i.e the superior rectus or
In a 4th nerve palsy the involved eye is always higher.
STEP 2 : (which lateral direction has worse hypertropia )
If the left hypertropia increases on right gaze implicates a
left superior oblique or right superior rectus involvement.
Increase in the left gaze implicates that either the right
inferior oblique or left inferior rectus are involved.
In 4th nerve palsy the deviation IS WORSE ON
OPPOSITE GAZE . (WOOG)
STEP 3: ( in which head tilt direction is the hypertropia worse )
The head tilt test is performed with the patient fixating at
a straight ahead target at 3 mts.
Increase in left hypertropia on left head tilt implies the
left superior oblique is involved , and increase in right
hypertropia on left head tilt indicates the right inferior
rectus is involved.
In 4th nerve palsy the deviation is BETTER ON
In Right SO palsy , on right head tilt RSR will work thus the eye will move
4TH CONFORMATORY STEP: (is the hypertropia worse in
upgaze or downgaze)
If the left hypertropia increases on down gaze it confirms
that the left superior oblique is involved . Helps to rule
out mimickers like myasthenia and thyroid disease.
DOUBLE MADDOX ROD TEST
A unilateral 4th nerve palsy is characterized by less than
10 degree of cyclodeviation, while a bilateral palsy will
have more than 20 degree of cyclodeviation.
CHECKING 4TH CN FN IN 3RD CN PARESIS
Vertical actions cannot be tested as there is 3rd N involvement
To solve this , note a limbal or conjunctival landmark.
Ask the pt to look down. The pt will not be able to look down
as the eye is abducted and not adducted.
But the eye should intort as the SO works. Check for the
conjunctival landmark to see if the eye is intorting.
If the conjunctival landmark is moving the eye is intorting thus
the 4th CN is intact.
ACTIONS OF SUPERIOR OBLIQUE
1. Intorsion 2. Depression 3. Abduction
Occlusion: Double vision is restricted to the downward gaze,
occlude the lower third of the spectacle lens before the affected
eyewith semi opaque tape.