Fourth Nerve Palsy Flashcards
Neurogenic
What deviation would you expect in a fourth nerve palsy?
Deviation: Hypertropia and esotropia, bigger at near, and to affected side-L/R or tilted to affected side
Loss of Depression, incyclotorsion, relative abduction
What’s the pathway for a fourth nerve palsy?
- Originates at dorsal midbrain at the level of the inferior colliculus 2. R + L nucleus which decussate as move posterior out of the midbrain 3. Sweeps around midbrain and runs between posterior cerebral artery + superior cerebellar artery 4. Enters cavernous sinus and runs along wall below 3rd + above ophthalmic division of the 5th 5. Enters S.O.F above annulus of Zinn + Innervates SO muscle!
Whats the most likely aetiology for a 4th nerve palsy?
Acquired:
* Closed head trauma (BIL + many UNI)
* Microvascular
* Midbrain Stroke
* Intracranial tumours
* Myasthenia Gravis
Congenital:
* Mostly UNI
* Superior Oblique Tendon, complete absence, abnormal insertion or excessively lax tendon
* Autosomal dominant form of inherited congenital SO palsy
What are the tests you would want to carry out on a fourth nerve palsy?
- History (ask about head trauma!) + VA
- CT N+D with/without AHP
- OM
- Pupils + Saccades
- BHHT (30 deg tilt to L + R @ 3m) +’ve > 5 ^ diff L+R + PARKS 3 STEP TEST!
- PCT N+D+9 positions of gaze ( Can use R + G filters to see if reversal in BIL)
- Lees/Hess
- Bgl gls to see if suppn or diplopia
- PFR ʹ horizontal and vertical (might be extended)
- Double Maddox Rod/Synoptopher/Torsionmeter/Dulley Adaptation on Lees Screen = Measure Excyclotorsion
What are the symptoms and signs of a 4th nerve palsy?
- Large hyperphoria (>20 dioptres) in congenital
- Diplopia very symptomatic to one side
Extended vertical PFR - Head tilt unaffected side
- Head turn to unaffected side + Sore/stiff neck if acquired
- Chin depression
Facial Asymmetry: Reduction in the distance between lateral canthus and the corner of the mouth on the side of the head posture (looks like half smile) CONGEN
Excyclodeviation causes diagonal non-fusible diplopia and can be seen on funduscopy
What is the head posture in a 4th nerve palsy?
R 4th nerve palsy = LEFT head tilt + LEFT head turn + chin depression
Also facial asymmetry if congenital
how do you know if a Bielshowsky head tilt test is positive?
- Performed at 3 metres
- Head is tilted 30 Degrees to the affected side and if the hypertropia increases then a SO palsy is present
- Head tilt to the unaffected side should show very little difference in the deviation suggesting a Contralateral SR u/a
- Positive result should be minimum 5^ difference from tilting right to left
What is parks 3-step test?
- Cover Test performed in Primary Position
- Alternate Cover Test performed on dextroversion and laevoversion to assess the greater vertical deviation
- BHHT is then performed tilting 30 degrees right and left and noting the increase in hyperdeviation
What pattern do congenital 4ths usually have?
V pattern esotropia (with hyperdeviation of non-fixing eye)
what are the differences between a congenital 4th and an acquired 4th?
Congenital have enlarged vertical fusion ranges, facial asymmetry more likely, not aware head posture but may be evident in childhood photos, not symptomatic about excyclotropia
What is the difference between unilateral and bilateral 4th nerve palsies?
– Head postures: UNI will have contralateral head tilts whereas BIL will have chin depression
– BHHT: Will be positive to one side in UNI but positive on both sides in BIL
– Hypertropia: No reversal (L/R - R/L) and greater than 5 dioptres in UNILATERAL, and reversal (R/L –> L/R) in BIL (<5 dioptres) - Can test with red/ green filters on R+L depression
– TORSION: uni = less than 10 degrees and not symptomatic, bil = more than 10 degrees and symptomatic in acquired only.
– V pattern more common in BIL than UNI
What are the muscle sequalae in 4th nerve palsy?
- Underaction of Ipsilateral SO (no ptosis)
- Overaction of Contralateral IR
- Overaction of the Ipsilateral IO
- Inhibitional palsy of Contralateral SR (ptosis)
UNDER OVER OVER UNDER
SAME DIFF SAME DIFF
Z pattern
How do you measure torsion?
Double Maddox rod
Torsionometer
synoptopher
Dulley adapter on LEES
Maddox Wing
treatment non surigcal for 4th np
- Some patients adopt an AHP to obtain a comfortable area of BSV. Others either find any head posture uncomfortable or are simply unable to achieve a field of single vision.
Prisms may be helpful, especially in cases in which a spread of concomitance has developed.
Sector occlusion to spectacle lenses can be helpful in eliminating diplopia, which is present only in extremes of gaze.imply unable to achieve a field of single vision
Surgical intervention for patients with acquired palsies should be delayed until no further recovery is seen to be taking place, which usually means that observation should be continued for 6–12 months.
when is surgery indicated for 4th np and what depends on
Surgery: - Delayed until no further recovery seen (6-12 months)
- Depends on degree of residual superior oblique muscle paresis / muscle sequelae / longstanding / horizontal deviation / patterns
Up to 15^ in PP corrected by weakening ipsilateral IO (some found up to 25^)
How much SO limitation?
> -2, strengthening needed especially if V-pattern & excyclo
Torsion – strengthening SO (one or both)
