Horizontal Gaze Palsy

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One and a Half Syndrome
Shirley H. Wray, M.D., Ph.D. Professor of
Neurology, Harvard Medical School Director, Unit
for Neurovisual Disorders Massachusetts General
Hospital
2
The One-and-a-Half Syndrome

• On horizontal gaze there is
• An ipsilateral gaze paresis or palsy
• An internuclear ophthalmoplegia (INO) on
  contralateral gaze
• At rest, the eyes are
• Orthophoric, or, in acute stage
• Ipsilateral eye esotropic or
• Contralateral eye exotropic (Paralytic pontine
  exotropic)

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• Three possibilities to account for an
  ipsilateral horizontal gaze palsy may be due to
  unilateral lesion affecting
• The ipsilateral PPRF only
• The ipsilateral abducens nucleus alone
• Both the ipsilateral PPRF and abducens nucleus

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Abducens Nucleus

• All the cells necessary for ipsilateral
  horizontal gaze
• Motoneurons whose axons form the sixth nerve
  (VIN) to innervate the ipsilateral lateral rectus
  muscle
• Internuclear neurons which send axons across the
  midline to opposite MLF and ultimately to the
  medial rectus motoneurons in the contralateral
  oculomotor nucleus (III N).

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Pathogenesis of Certain Signs
Ocular Motor Possible Pathophysiologic
Deficit Substrate
Ipsilateral adduction weakness Ipsilateral slowed
abducting saccades Contralateral abduction
nystagmus
Interruption of axons of abducens internuclear
motoneurons Inadequate inhibition of medial
rectus motoneurons Impaired inhibition of
contralateral medial rectus or Interruption of
descending fibers to contralateral abducens
nucleus or Involvement of adjacent PPRF
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Neurology 1983 33971-980
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• Reported Boston Total cases series
• Brainstem Infarct 12 4 16
• Multiple Sclerosis 2 14 16
• Pontine Glioma 2 1 3
• Arteriovenous Malformation 1 0 1
• Pontine Hemorrhage 8 0 8
• Basilar Artery Aneurysm 0 1 1
• Cerebellar Astrocytoma 2 0 2
• Metastatic Melanoma 1 0 1
• Ependymoma Fourth Ventricle 1 0 1
• 29 20 49

Table 1. The one-and-a-half syndrome Etiology
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Diplopia 12 Blurred Vision 8 Oscillopsia
4 Difficulty looking to one
side 2 Quivering of the eye 1 No visual
complaint 3
Table 2. One-and-a-half syndrome (N 20) Visual
Symptoms
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(N 20) Gaze-evoked upbeat
nystagmus 12 Skew deviation 8 Horizontal
ipsilateral gaze nystagmus 4 Rotary component
to horizontal ipsilateral gaze nystagmus 2 Sponta
neous nystagmus to the contralateral
side 1 Absent or impaired convergence 5 Sacc
adic vertical pursuit 9 Gaze-evoked downbeat
nystagmus 4 Impaired upward gaze 1
(N 11) Exotropia 4 Esotropia
3 Orthotropia 4
Table 3. One-and-a-half syndrome (N 2011)
Associated ocular motility signs
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Cranial Nerve Involvement I 0 II 1 III
0 V 3 VII 4 VIII 2 IX 3 XI 0
XII 2 Horners Syndrome 1 Weakness or
spasticity 6 Sensory deficits 7 Abnormally
brisk or asymmetric reflexes 5 Extensor plantar
responses 9 Incoordination 10
Table 4. One-and-a-half syndrome (N 20)
Associated neurologic signs
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Esotropia of the ipsilateral eye
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Patient 1. The one-and-a-half syndrome (A) Mild
left INO looking right. (B) Esotropia OS
(ipsilateral) in the primary position of gaze.
(C) Horizontal conjugate gaze palsy attempting to
look left. (D) Normal convergence.
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Paralytic Pontine Exotropia
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Patient 2. Paralytic pontine exotropia. (A)
Horizontal conjugate gaze paresis looking right.
(B) Exotropia OS (contralateral) in the primary
position of gaze. (C) Right INO looking left. (D)
Right peripheral-type ipsilateral facial palsy.
(E) Impaired convergence.
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• Patient 2. Paralytic Pontine Exotropia
• Horizontal conjugate palsy looking right.
• Exotropia OS contralateral in the primary
  position of gaze.
• Right INO looking left
• Right peripheral-type ipsilateral facial palsy
• Impaired convergence

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• In paralytic pontine exotropia the exotropic eye
  shows
• Abduction nystagmus during attempts to move it
  laterally
• Extreme slowness of adduction saccades when
  eye fixing to move it to the midline

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• Paralytic Pontine Exotropia attributed to
• Tonic contralateral deviation of the eyes
• Implies acute ipsilateral PPRF lesion
• Failure of ipsilateral eye to deviate medially
  explained by the INO

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Paralytic pontine exotropia OS
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Paralytic pontine exotropia right horizontal gaze
palsy
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http//www.library.med.utah.edu/NOVEL