4th nerve palsy Flashcards
What is the 4th cranial nerve?
Trochlear nerve
What does the 4 nerve innervate?
SO -superior oblique muscle (LR6SO4)
What does the SO do?
intorts (down and in)- primary action of SO depression and abduction
If these movements of the SO are restricted, what will happen?
hypertropia in primary position
What will patient complain of?
vertical and torsional diplopia
When is the diplopia worse?
At near (opposite of 6th nerve palsy)
Why is the 4th nerve vulnerable to injury
Due to its long pathway from the back of the brain to the eye
What does cover test show?
Hypertropia of the affected eye in primary position The size of the deviation will worsen and the eye will elevate if the patient’s head is tilted to the affected side. There may only be a hyperphoria present when the patient’s head is tilted to the unaffected side
What are most types of 4th nerve palsies?
congenital
What is the cause of a congenital 4th nerve palsy?
SO tendon loose, absent or abnormally inserted or SO muscle abnormally developed or trochlea is abnormally developed or absent.
Why can a congenital 4th nerve palsy cause symptoms/dipl?
Decompensation of a longstanding congenital palsy
What causes decompensation?
Age - the deviation becomes too difficult to control; the patient may also have symptoms of asthenopia and headaches.
Illness
How do you manage congenital 4th nerve palsy?
If detetcted in childhood, any signiicant refractive error should be prescribed AND routine referral to orthoptics to conirm diagnosis and for the management of any associated amblyopia.
How do you know that no further treatment will be required for the child?
If the child can maintain binocular single vision with a comfortable compensatory head posture.
If further treatment is required for congenital 4th nerve palsy, what will it be for adults and children?
Surgery first choice in adults and children to eliminate/reduce CHP, cosmetic, reduce symptoms and prevent decompensation.
What is done first in adults with congenital 4th nerve palsy to check surgery will work?
Frensel prism- Small amounts can be incorporated but tend to increase with time and require surgery. Warn px they may need more than 1 surgery.
What type of surgery is done?
Surgery is easier to do IO recession by weakening procedure but if not much IO overaction or SO tendon lax then tuck SO but carries risk of duane’s
Further surgery- contralateral IR recession
What is an acquired 4th nerve palsy commonly caused by?
head trauma typically to back of head
What are other causes of acquired 4th nerve palsy?
vascular or neoplasm
How do you differentie between aquired and congenital?
recent or longstanding diplopia/symptoms
when they look down everything will be tilted
How do you manage acquired 4th nerve palsy?
Urgent referral (within one week) to orthoptics and ophthalmology to conirm diagnosis and to complete further medical and neurological evaluations.
How do you manage a longstanding congential 4th nerve palsy that has recently decompensated?
Refer urgently to rule out any sinister cause of decompensation, particularly in older patients (over 60 years) with an increased risk of vascular incident.
What can be done to alleviate patien’t symptoms temporarily?
Fresnel vertical prisms may be prescribed to alleviate the symptoms of diplopia or an occlusive patch or contact lens can be used until the condition resolves.
How long does it take for vascular cause palsy to recover and why would they have prism permenantly?
Most vascular cases resolve within 3–6 months or at least, once stabilised, vertical prisms can be added permanently to the patient’s glasses to maintain binocularity.
What if they still get diplopia and prisms don’t help?
Where there is insuficient resolution and the deviation is too large to control with prisms, surgery may be considered.
What is unilateral 4th nerve palsy?
Eye elevates more at NEAR than distance and also extorts and adducts.
In primary position eye either hyperphoric or hypertropic but then hyperdeviation becomes apparent/increase when you gaze to the opposite side of the eye with the palsy eg. RSO paly, overactions (elevate, extort, adduct) increases when you look to the lef
What is the CHP in unilateral 4th nerve palsy?
head tilt and head turn to OPPOSITE side and chin depression so eyes go up. If CHP is pronounced then its longstanding
Describe the muscle sequele in unilateral 4th nerve palsy
SO underaction, IO overaction, Contralateral IR overaction (hering’s opp eyes), Contralateal SR underaction (sheringtons-same eyes)
Describe muscle sequele in bilateral 4th nerve palsy
Bilateral IO overaction, bilateral SR underaction, bilateral IR overactio
What is symmetrical 4th nerve palsy?
eyes fairly level in primary position. CT in PP may not notice defect
What is asymmetrical bilateral 4th nerve palsy?
hyper deviation in eye with the bigger palsy.
OM shows hyperdeviation reverse in contralateral field so when u look left, the RE is higher and when u look right the LE is higher.
OM also shows torsion if acquired and CHP chin down. Bilateral is difficult to see and may only notice it’s bilateral after unilateral SO palsy surgery.
What should you always assume about a 4th nerve palsy?
Always assume it’s bilateral until proven otherwise.
