5 Supranuclear disorders - HORIZONTAL Flashcards
What is the main function of a saccade and what speed is it?
To bring an object of interest onto the fovea
Fast
What is the main function of nystagmus (quick phase) and what speed is it?
To direct eyes onto oncoming visual scene and reset eyes after rotation.
Fast
What is the main function of the smooth pursuit and what speed is it?
To hold a slow-moving target on the fovea
Slow
What is the main function of optokinetic movement and what speed is it?
To hold images steady on the retina during sustained head rotation.
Slow
What is the main function of vestibular movement and what speed is it?
To hold images steady on the retina during brief head rotation.
Slow
What is the main function of vergence movements and what speed is it?
To move the eyes in opposite directions to maintain bifoveal fixation and a single image
Slow
What are the three cell types present in the horizontal gaze brainstem pathway?
Excitatory burst cells
Inhibitory burts cells
Omnipause neurons
What is the action of the excitatory burst cells?
Generate ipsilateral horizontal saccades
What is the action of the inhibitory burst cells?
Decrease firing rate of contralateral VIth motor neurons and internuclear neurons
What is the action of the omnipause neurons?
Inhibit both burst cells.
What is the role and location of the frontal eye fields?
Role - Production of saccades on opposite side of side of the stimulus, selects target and commands movement
Location - Frontal cortex
What is the role and location of the Parietal-temporal-occipital region?
Role - production of smooth pursuit movements
Location - Cerebral cortex, includes portions of patietal, temporal and occipital lobes. End of Sylvian fissure
What is the role and location of the Paramedian pontine reticular formation (PPRF)?
Role - Generating horizontal conjugate gaze
Location - Brainstem
What is the role and location of the medial longitudinal fasciculus (MLF)?
Role - facilitates yoked eye movements, important connection through the MLF links contralateral abducens nucleus with ipsilateral medial rectus subnucleus
Location - Fibre tract that extends from spinal cord to oculomotor nucleus
What is the role and location of the Rostral Interstitial Nucleus of the MLF (riMLF)?
Role - Generate vertical conjugate fast movements up, down and torsional, but most important in generating downgaze. Vertical and torsional gaze holding.
Location - Mesencephalon at rostral termination of MLF. Adjacent to interstitial nucleus of Cajal.
What is the role and location of the posterior commissure and the nucleus of the posterior commissure?
Role - important in generating upward gaze movements
Location - Dorsal to the riMLF
What is the role and location of the superior colliculus?
Role - Both ocular motor and sensory function. Generates visually directed saccades independently (may play a role in smooth pursuits)
Location - Dorsal surface of midbrain, below the thalamus.
What is the role and location of the cerebellum?
Role - Modulation of all types of eye movement. Long term adaptation to compensate for ocular motor dysmetria. Gaze holding, smooth pursuit, combo head and eye tracking, saccade size, adjustment of vestibulo-ocular reflex
Location - level of the brainstem under the occipital lobe.
What is the route of saccade action?
Start: contralateral frontal eye fields (frontal lobe)
→ superior colliculus
→ PPRF
→ horizontal gaze centre (VIth nerve nucleus)
→ ipsilateral LR and contralateral MR (via MLF)
What is the route of smooth pursuit action?
Start: ipsilateral parieto-occipital lobe
→ superior colliculus
→ PPRF
→ horizontal gaze centre
→ ipsilateral LR and contralateral MR (via MLF)
What lesions lead to horizontal conjugate gaze deficits?
- Cerebral cortex or pontine lesions
What are examples of conjugate gaze limitations?
o Unilateral gaze palsy
o Saccadic palsy
o Palsy of Smooth pursuit
o Bilateral gaze palsy
o Conjugate gaze deviation
o Ocular motor apraxia
What are some features of a unilateral horizontal gaze palsy?
Eyes deviated to opposite side
Mild damage = selective, slow ipsilateral saccades, min limitation, spared pursuit,
Severe lesion = complete ipsilateral saccadic and pursuit palsy large
lesion leads of deficient VOR and neural integrator, gaze evoked nystagmus towards intact contralateral field and affected vestibular nuclei
Normal gaze to contralateral side
Full vertical gaze
Normal VOR (Doll’s head) but VOR does not improve movement if VIth nuclear lesion
May be long lasting
What is the aetiology behind unilateral horizontal gaze palsies?
Ipsilateral pontine lesion – affecting PPFR rostral to VIth nucleus
CVA tumour, MG
Compression from external tumour
Name some differential diagnosis of unilateral horizontal gaze palsies
o Duane’s syndrome
o One and a half syndrome
What are features of unilateral saccadic palsies?
o Eyes slowly deviate towards side of lesion
o Contralateral saccadic palsy/paresis
o Loss of fast phase OKN
o Pursuit bilaterally impaired, more towards side of lesion
o Intact VOR
o Improve with time, subtle defects remain
o Difficulty maintaining gaze away from affected frontal cortex – small corrective saccades gaze paretic nystagmus
What is the aetiology behind unilateral saccadic palsies?
Contralateral frontal lobe lesion
CVA – haemorrhage or infarct
Tumour
What is a differential diagnosis of unilateral saccadic palsies?
o Episodic saccadic palsy = epilepsy
What are some features of a smooth pursuit palsy?
o ‘Cog wheel’ pursuit
o Corrective saccade
o Slow phase OKN affected when stripes rotated towards lesion
o Parietal-occipital lesion – contralateral HH
What is the aetiology behind smooth pursuit palsies?
Lesion in parieto-occipital lobe damage
CVA or tumour
What are features of a bilateral gaze palsy?
o Loss of saccadic movement to both sides
o Loss of smooth pursuit
o Intact VOR
What is the aetiology of a bilateral gaze palsy?
o Bilateral pontine lesions restricted to PPRF or VIth nerve nucleus
What are differential diagnosis of bilateral gaze palsies?
o CPEO
o TED
o MG
o Bilateral IIIrd and VIth
What are features of ocular motor apraxia (acquired balints syndrome)?
o Difficulty initiating voluntary horizontal saccades
o Difficulty initiating reflexive saccades and smooth pursuit in all directions
o Simultanagnosia
o Optic ataxia
o Frequently have associated dementia and visual field defects
What is the aetiology behind ocular motor apraxia (acquired balints syndrome)?
Extensive bilateral cerebral disease – parieto-occipital
What are the features of ocular motor apraxia (congenital)?
o Present in infancy
o Apparent visual inattention
o Once develop head control characteristic head thrusts and excessive blinking occur
o Inability to execute voluntary saccades
o Vertical saccades and pursuit not affected
o Head thrust: manoeuvre to change fixation
o Excessive blinking
What is the aetiology behind ocular motor apraxia (congenital)?
o Associated with CNS disorders
agenesis of corpus callosum
Collicular abnormalities
Cerebellar vermian dysplasia (e.g. Joubert syndrome)
What are features of spasm near reflex?
Variable esotropia
Pseudo VIth nerve palsy
Signs of dorsal midbrain syndrome
Fasicular IIIrd nerve palsy
Skew deviation
What is the aetiology behind spasm near reflex?
Usually psychogenic
Rarely: head trauma, dorsal midbrain syndrome, lesion in brainstem, lesion in diencephalon, intoxication, Wernicke’s encephalopathy
What is the differential diagnosis for spasm near reflex?
Bilateral VIth nerve palsies
What are features of convergence insufficiency?
NPC less than 10cm
Or can only be maintained at 10cm with effort
Diplopia
Asthenopic symptoms
Blurred vision
Exophoria at near
What is the aetiology behind convergence insufficiency?
Primary – no other cause found
Secondary – Parkinson’s, PSP, INO
What are the two differential diagnosis for convergence insufficiency?
Exophoria – convergence weakness type
Accommodation insufficiency or fatigue
What are the features of convergence paresis/paralysis?
Diplopia at near, or closer than infinity for paralysis
Fatiguability while reading/near visual task
Asthenoptic symptoms
Blurred vision at near
Does not respond to orthoptic exercises
Exotropia/phoria at near (constant XT within infinity for paralysis)
What is the aetiology behind convergence paresis/paralysis?
Age
Less commonly, dorsal midbrain syndrome, Parkinson’s, MS, encephalitis, Cholinergic drugs, morphine, ocular inflammation, alcohol
What are the differential diagnosis for convergence paresis/paralysis?
Decompensated exophoria
Primary exotropia
Secondary exotropia
Accommodation insufficiency or fatigue
Uncorrected hypermetropia
Intermittent exotropia, simulated by accommodation
What are the features of divergence paresis/paralysis?
Can occur in isolation or in association with other neurological signs
Uncrossed diplopia
Concomitant esotropia, Distance>Near
Normal ocular movements, full abduction
Paresis – defective negative fusional amplitudes
Paralysis – absent negative fusional amplitudes
Associated convergence weakness reported (Roper-Hall & Burde, 1987)
What is the aetiology of divergence paresis/paralysis?
Lack of agreement of location of divergence centre – agree in brainstem
Intracranial tumour, raised ICP, infection, Miller-fisher syndrome and vascular disease
What are differential diagnosis of divergence paresis/paralysis?
Acquired VIth nerve palsy
Convergence spasm
TED
Esophoria with divergence weakness
Distance esotropia
What are some features of Wernike’s Encephalopathy?
Triad: Ophthalmoplegia, confusion and gait ataxia
Abduction weakness
Gaze-evoked nystagmus
INO
Upbeat nystagmus
Impaired VOR
Horizontal and vertical gaze palsies that may progress t complete ophthalmoplegia
Bilateral but may be asymmetric
What is the aetiology for Wernike’s Encephalopathy?
Lesions occur throughout brainstem, thalamus, hypothalamus, cerebellum
Thiamine B1 deficiency
Most commonly seen in alcoholics
