Horizontal gaze centre: **pons**
- PPRF
- Sixth nerve nucleus
- Mediate to medial rectus subnucleus in midbrain via MLF (an interneurone)

Vertical gaze centre: **midbrain**
- Thalamo-mesencephalic junction

Saccades
- Contralateral frontal eye fields

Pursuits
- Ipsilateral parieto-occipital-temporal (POT) region

<Note>

For saccades and pursuits, the supranuclear and infranuclear pathways are the same.

</Note>

See separate Chapter on supranuclear control of eye movements.

The vestibulo-ocular reflex (Doll’s head manoeuvre) communicates with the infranuclear pathways (nucleus, peripheral nerve etc downstream.
- Therefore an **intact** VOR may suggest the deficit is **supranuclear**


## Horizontal gaze abnormalities

Stimulation of the horizontal gaze centre (PPRF/sixth nerve nucleus in**pons**) on one side causes a conjugate movement of the eyes to the same side

### Horizontal gaze palsy
- Lesions of the PPRF or sixth nerve nucleus
    - A lesion to the sixth nerve nucleus disrupts signal to both:
      - The lateral rectus, and
      - The third nerve subnucleus for medial rectus (via the MLF)
    - Therefore a nuclear sixth produces a horizontal gaze palsy to the ipsilateral side

- Eyes cannot move across the midline to the side of the lesion (cannot look in direction of lesion)
- Vestibulo-ocular reflex is **preserved** with a PPRF lesion (supranuclear) but**not**in a VI nucleus lesion
- **No diplopia**

### Internuclear ophthalmoplegia
- Lesion in the MLF
    - Demyelination
    - Stroke
    - Tumour

<HotTopic>
The medial longitudinal fasciculus (MLF) connects the sixth nerve nucleus (pons) with the contralateral medial rectus subnucleus of the third nerve nuclei (midbrain).
</HotTopic>

- Unilateral INO:
    - Straight eyes in the primary position
    - Loss of adduction of the ipsilateral eye (to the lesion)
    - Nystagmus of the contralateral eye on abduction
    - Normal gaze to the side of the lesion
    - Convergence is intact if lesion is small and anterior in the MLF and below the midbrain
      - There is supranuclear control to the third nerve nuclei for convergence that is independent of the sixth nerve nucleus
    - **Slow adduction saccadic velocity** on the affected side compared to abduction velocity of the contralateral eye: this is a cardinal feature

- Bilateral INO:
    - Left gaze: right eye cannot adduct and left eye ataxic nystagmus (overshoot of the eye)
    - Right gaze: left eye cannot adduct and right eye ataxic nystagmus
    - A rostral midbrain lesion also gives a convergence deficit causing bilateral exotropia: ‘wall-eyed bilateral INO (WEBINO)

- May be associated with:
    - Abnormal VOR
    - Skew deviation: ipsilateral hypertropic eye

### One and a half syndrome (a dorsal pontine syndrome)
- Lesion of the MLF and PPRF/sixth nerve nucleus: typically a**pontine**stroke/lesion
- Ipsilateral horizontal gaze palsy and ipsilateral INO
- **Contralateral abduction** is the only preserved horizontal eye movement (vertical gaze is unaffected)

### Tonic gaze deviation
- Damage to the frontal eye field
    - Strokes, trauma, tumour

- Loss of initiation of eye movements to the contralateral side
- Eyes deviate to the ipsilateral side

## Vertical gaze palsies

The vertical gaze centre is located at the junction between the thalamus and the **midbrain** (thalamo-mesencephalic junction).

### Parinaud syndrome (dorsal midbrain syndrome)
The dorsal midbrain contains
- Edinger-Westphal nucleus (CNIII)
- Pretectal nuclei

Lesion in the posterior commissure and pretectal areas
- Hydrocephalus (eg. aqueduct stenosis)
- Meningitis
- Tumour eg. pinealoma in children
- Trauma/head injury
- AV malformation
- Demyelination
- CVA
- Degenerative (Wernicke’s encephalopathy)

Features
- **Lid retraction** bilaterally (Collier’s sign): due to disruption of inhibitory input to the levator
- **Near-light dissociation** with mydriasis: due to disruption of the light pathway, with sparing of the near pathway which is more rostral
- **Convergence-retraction nystagmus**: due to co-contraction of medial and lateral recti on attempted upgaze (not a true nystagmus)
- **Supranuclear upgaze palsy**(cp PSP): initially saccades, then pursuit movements, then VOR. Due to posterior commissure disruption where the upgaze pathways converge

- Others:
    - Straight eyes in primary position
    - Loss of convergence
    - Skew deviation

- An MRI of the brainstem is indicated

<Note>
Upgaze neural pathways converge at the posterior commissure, however downgaze pathways are bilateral. Hence, upgaze deficit is much more common and earlier in dorsal midbrain syndrome; downgaze is only affected latterly.
</Note>

### Progressive supranuclear palsy aka Steele-Richardson-Olsezewski syndrome
- Rare progressive neurodegenerative disease: tau protein accumulation
- An atypical Parksinsonian syndrome
- Onset over age 40
- Supranuclear gaze palsy primarily of **downgaze first**
- Latterly, loss of horizontal movements and global gaze palsy
- **Loss of convergence**
- Lid apraxia can lead to corneal exposure
- Square wave jerks: ‘nystagmoid’ movements (not a true nystagmus)
    - Saccadic intrusion: small amplitude, horizontal shift/intrusion away from fixation followed by a pause then a quick return to fixation
    - Often seen in normal patients
    - \>9 per minute associated with Parkinson’s disease or progressive supranuclear palsy

- Pseudobulbar palsy
- Extrapyramidal signs, rigidity
- Frequent falls due to gait problems
- Dementia

### Skew deviation
- Rare
- Vertical deviation with cyclotorsional disturbance
    - Not due to cranial nerve palsy or muscle issue
    - Typically concomitant (ie **both** eyes hypertropic)
    - But may be incomitant (ie. one hypertropic and the other hypotropic) which may be confused with a ** fourth nerve palsy**. Consider a skew and fourth nerve palsy when presented with any vertical gaze deviation
      - The upright-supine test can be used to differentiate: with a skew, the vertical deviation will**decrease**(>50%) with the patient supine compared to upright (but will remain constant with a fourth nerve palsy)

- Usually due to brainstem or cerebellar stroke
- May be associated with perceived tilting of the visual field (‘ocular tilt reaction’)

### Monocular elevation deficit (double elevator palsy)

- Congenital or acquired. Causes:
    - Type 1: **inferior rectus restriction**. Forced duction test positive
    - Type 2: deficient innervation to elevators
    - Type 3: supranuclear (eg lesions in the pretectum?)

- Congenital ptosis/**pseudoptosis** due to fascial attachments between levator and superior rectus
    - Dystrophy or maldevelopment of the levator and superior rectus complex
- Poor/absent Bells phenomenon
- Chin up posture
- Management: depends on forced duction test
    - Type 1: inferior rectus recession
    - Others: Knapp procedure: transposition of the medial and lateral recti to superior rectus


Horizontal gaze centre: pons PPRF Sixth nerve nucleus Mediate to medial rectus subnucleus in midbrain via MLF (an interneurone) Vertical gaze centre:…

Neuro-ophthalmology

Supranuclear Motility Disorders

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