4th nerve palsy

Question 1

What is the 4th cranial nerve?

Answer 1

Trochlear nerve

Question 2

What does the 4 nerve innervate?

Answer 2

SO -superior oblique muscle (LR6SO4)

Question 3

What does the SO do?

Answer 3

intorts (down and in)- primary action of SO depression and abduction

Question 4

If these movements of the SO are restricted, what will happen?

Answer 4

hypertropia in primary position

Question 5

What will patient complain of?

Answer 5

vertical and torsional diplopia

Question 6

When is the diplopia worse?

Answer 6

At near (opposite of 6th nerve palsy)

Question 7

Why is the 4th nerve vulnerable to injury

Answer 7

Due to its long pathway from the back of the brain to the eye

Question 8

What does cover test show?

Answer 8

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

Question 9

What are most types of 4th nerve palsies?

Answer 9

congenital

Question 10

What is the cause of a congenital 4th nerve palsy?

Answer 10

SO tendon loose, absent or abnormally inserted or SO muscle abnormally developed or trochlea is abnormally developed or absent.

Question 11

Why can a congenital 4th nerve palsy cause symptoms/dipl?

Answer 11

Decompensation of a longstanding congenital palsy

Question 12

What causes decompensation?

Answer 12

Age - the deviation becomes too difficult to control; the patient may also have symptoms of asthenopia and headaches.

Illness

Question 13

How do you manage congenital 4th nerve palsy?

Answer 13

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.

Question 14

How do you know that no further treatment will be required for the child?

Answer 14

If the child can maintain binocular single vision with a comfortable compensatory head posture.

Question 15

If further treatment is required for congenital 4th nerve palsy, what will it be for adults and children?

Answer 15

Surgery first choice in adults and children to eliminate/reduce CHP, cosmetic, reduce symptoms and prevent decompensation.

Question 16

What is done first in adults with congenital 4th nerve palsy to check surgery will work?

Answer 16

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.

Question 17

What type of surgery is done?

Answer 17

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

Question 18

What is an acquired 4th nerve palsy commonly caused by?

Answer 18

head trauma typically to back of head

Question 19

What are other causes of acquired 4th nerve palsy?

Answer 19

vascular or neoplasm

Question 20

How do you differentie between aquired and congenital?

Answer 20

recent or longstanding diplopia/symptoms

when they look down everything will be tilted

Question 21

How do you manage acquired 4th nerve palsy?

Answer 21

Urgent referral (within one week) to orthoptics and ophthalmology to conirm diagnosis and to complete further medical and neurological evaluations.

Question 22

How do you manage a longstanding congential 4th nerve palsy that has recently decompensated?

Answer 22

Refer urgently to rule out any sinister cause of decompensation, particularly in older patients (over 60 years) with an increased risk of vascular incident.

Question 23

What can be done to alleviate patien’t symptoms temporarily?

Answer 23

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.

Question 24

How long does it take for vascular cause palsy to recover and why would they have prism permenantly?

Answer 24

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.

Question 25

What if they still get diplopia and prisms don’t help?

Answer 25

Where there is insuficient resolution and the deviation is too large to control with prisms, surgery may be considered.

Question 26

What is unilateral 4th nerve palsy?

Answer 26

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

Question 27

What is the CHP in unilateral 4th nerve palsy?

Answer 27

head tilt and head turn to OPPOSITE side and chin depression so eyes go up. If CHP is pronounced then its longstanding

Question 28

Describe the muscle sequele in unilateral 4th nerve palsy

Answer 28

SO underaction, IO overaction, Contralateral IR overaction (hering’s opp eyes), Contralateal SR underaction (sheringtons-same eyes)

Question 29

Describe muscle sequele in bilateral 4th nerve palsy

Answer 29

Bilateral IO overaction, bilateral SR underaction, bilateral IR overactio

Question 30

What is symmetrical 4th nerve palsy?

Answer 30

eyes fairly level in primary position. CT in PP may not notice defect

Question 31

What is asymmetrical bilateral 4th nerve palsy?

Answer 31

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.

Question 32

What should you always assume about a 4th nerve palsy?

Answer 32

Always assume it’s bilateral until proven otherwise.