Common cause of vertical strabismus

## Anatomy nuggets

- Nucleus lies just beneath the IIIn nucleus in the midbrain at the level of the inferior colliculus
- **Decussates** and exits the midbrain posteriorly then curves around to travel anteriorly
- Travels in the lateral wall of the cavernous sinus inferolateral to the IIIn
- Enters the orbit through the SOF but **outside** of the annulus

## Aetiology

- 1/3rd are **congenital** but may manifest in adulthood
- Acquired:
    - Traumatic (especially bilateral): fourth nerve palsy is the most common nerve palsy following closed head injury
    - Microvascular
    - Idiopathic
    - Iatrogenic (eg ENT or neurosurgery)
    - Tumour eg pinealoma
    - Demyelination
    - Vasculitis
    - Meningitis
    - Cavernous sinus lesion
    - Tolosa-Hunt syndrome
    - HZO

## Features of congenital fourth

- Large vertical fusion range (10-15 PD)
- High concomitance (may also be present in longstanding acquired lesions)
- Head tilt on old photos
- Facial asymmetry

## Clinical features

- Vertical and torsional diplopia
- Head tilt **away** from the side of the lesion
- Aesthenopia (eye strain)
- Ipsilateral hypertropia/phoria exacerbated on downgaze or head tilt**towards**the side of the lesion
- Reduced depression especially on adduction
- Extorsion: can be seen on fundoscopy compared to fellow eye (eg. consider fundus photos)

- Parks-Bielschowsky 3-step test
    - 1\. Cover test: identify higher eye
    - 2\. Cover test with gaze to the right, then left: identify where deviation/diplopia is greatest
      - Ie. if greatest in adduction, then obliques involved; if greatest in abduction, then vertical recti involved
      - Step 2: tells you whether superior or inferior muscles
    - 3\. Cover test with head tilt to the right, then left: identify where deviation is greatest
      - Superior muscles cause intorsion, while inferior muscles extort
      - Step 3: tells you which eye

<HotTopic>
Bilateral fourth nerve palsies (eg. traumatic or congenital): **reversing hypertropia**

- R/L on left gaze and L/R on right gaze

- **V patternesotropia**

- Chin down head posture

- **>10 degrees** of excyclotorsion

- Failure of adduction on depression bilaterally

</HotTopic>

## Tests

- Check old photos for abnormal head posture
- Vascular risk factors (including arteritis)
- Consider neuroimaging if unclear cause or no recovery after 3 months
- Orthoptists monitoring including Hess charts
- Double maddox rod: measure cyclotorsion

<HotTopic>
Vertical fusion amplitudes: in congenital fourth, the misalignment from birth means patients are often able to fuse vertical deviations much larger than the normal 2-3 dioptres. Measuring these can be helpful in identifying a longstanding congenital fourth that may have recently decompensated.
</HotTopic>

## Management

- Conservative: management of symptomatic diplopia with prisms, occlusion, CL
- Botox
- Muscle surgery:
    - Harada-Ito for excyclotorsion
    - Inferior oblique weakening (eg. myectomy, recession) for IOOA


Common cause of vertical strabismus Anatomy nuggets Nucleus lies just beneath the IIIn nucleus in the midbrain at the level of the inferior colliculus…

Neuro-ophthalmology

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