supranuclear disorders of ocular motility

SUPRANUCLEAR AND INTERNUCLEAR DISORDERS OF OCULAR MOTILITY

DR ARPITA

• Extraocular muscles are supplied by 3,4,6 th cranial nerves which have their nuclei in the brainstem

• Centres controlling the nuclei – Supranuclear• Pathways connecting the nuclei – Internuclear• Nerves supplying the EOM - Infranuclear

• The eyes move in SIX WAYS

FAST EYE MOVEMENTS(300°-600°/SEC)

1) SACCADES

2) NYSTAGMUS

SLOW EYE MOVEMENTS(5°-50°/SEC)

1) SMOOTH PURSUIT

2) OPTOKINETIC

3) VESTIBULAR

4) VERGENCE

SACCADES

• Derived from french word “Saquer” which means to pull or tug

• REDIRECT eyes from one target to another

• Voluntary or reflex ( in response to visual , auditory or pain stimulus )

• Always conjugate

• Ballistic – once initiated they cannot be stopped or modified

• Speed of saccade is directly proportional to size of movement Velocity of a larger saccade is faster than the velocity of a slow saccade , this is known as Main sequence

• Visual suppression occurs - even though the visual world is sweeping across retina , there is no sense of a blurred image

Pathways for saccades

CROSSED PATHWAY

Synthesis of a saccade- “pulse step”

Clinical examination

Thefixation objects should be presented at an angular separationof about 20 to 30°.

Clinical examination

• SPEED - slowing of saccades can be seen in AIDS dementia complex , Lipid storage disorders , PSP , drug intoxications

• SMOOTHNESS – affected in cerebellar diseases

• ACCURACY – Hypometric or Hypermetric , affected in cerebellar diseases

SMOOTH PURSUIT

• Slow eye movements that permits the eyes to conjugately follow/track a target during movements of the target or observer or both

• Have the capcity for compensation unlike saccades - when speed of target is varied after initiation of the movement , speed of pursuit can be varied.

• Initiated by a slow moving target across the fovea

• Visual fixation holds the image of a stationary object on the fovea

Pathway for pursuit movements

DOUBLE DECUSSATION

• Parieto – occipito – temporal region is the confluence of Brodman areas 19, 37 and 39

• A pure occipital lobe lesion will not affect smooth pursuit movements

• Deep parietal lobe lesions disrupt smooth pursuit to ipsilateral side

VESTIBULAR REFLEX

• Coordinates eye movements with head movements, holds image steady during brief head rotations

• Stimulation of Ampulla of horizontal semicircular canal conjuate movement towards contralateral side

• Information from anterior and posterior semicircular canals - combination of vertical and torsional eye movements

“COWS”

OPTOKINETIC REFLEX

• Stimulus – sustained head rotation• With sustained head rotation at a constant

velocity , vestibular response fades and optokinetic response takes over

• OKN prevents a continuous blur from relative motion of the moving visual field .

Turning the drum to the right elicits an ipsilateral pursuit movement to the right and a contralateral saccade to the left.

VERGENCE

• Allows bifoveation of an object moving in Z axis

• Stimuli – • Retinal blur – accomodative vergence• Disparity of location of images- fusional

vergence• Pathway : Occipital cortex – midbrain reticular

formation – 3rd nerve nucleus

INTERNUCLEAR PATHWAYS

• Vertical saccades require simultaneous activation of both FEF

• Unilateral activation of the riMLF generates torsional eye movements

• Right riMLF – clockwise movements• Left riMLF – anticlockwise movements

Supranuclear disorders...

• Affect both eyes

• Do not produce diplopia

• Dolls eye phenomenon and Bells phenomenon remain intact

DISORDERS OF HORIZONTAL GAZE

A) SACCADIC DISORDERS• INABILITY TO PRODUCE SACCADES1) Frontal lobe lesions - Injury• Cannot generate contralateral saccades• Preferential gaze to affected side• Pursuit , OKN ,VOR are normal• Recovers after several weeks due to activation

of projections from ipsilateral FEF to PPRF

• 2) Congenital ocular motor apraxia (COMA)

• Cannot initiate voluntary horizontal saccades• Vertical saccades are normal• “ Head thrusting occurs ”• Becomes less prominent with age

• 3) Acquired ocular motor apraxia• Aka Balints syndrome• Seen in extensive B/L cerebral disease (parieto

– occipital)• Simultagnosia – inability to perceive more

than one object at a time• Optic ataxia – inaccurate arm pointing• Dementia• Visual field defects

• SLOWING OF SACCADES1) Progressive supranuclear palsy• Aka Steel – Richardson – Olszewski syndrome• Progressive conjugate paresis of gaze in all

directions especially downward• Associated neurological symptoms include

dementia , dysarthria , nuchal and axial rigidity

• Recurrent falls early in course• Death within several years of diagnosis

• 2) Olivopontocerebellar degeneration

• Presents early in adulthood • Ataxia , slurred speech and dementia• Eye movements in all directions are

progressively affected• Eventually leads to total ophthalmoplegia

• Dysmetric saccades• Hypometric saccades are not necessarily

pathological;they can be the product of inattention or poor cooperation.

• Hypermetric saccades on the contrary are always pathological and strongly suggest the presence of a lesion in the cerebellar vermis.

• UNWANTED SACCADES• Square wave jerks – named for their

appearance of eye movement recordings• Sporadic saccades that return to fixation

within 100-200 msec• Greater than 1 degree = pathologic• Associated with cerebellar disease• Called as “ sed rate of CNS “ as more than

10/min is a non specific indicator of CNS disease

• Ocular flutter• Intermittent brief volley of horizontal

oscillations aroud fixation • No intersaccadic interval unlike square wave

jerks

• Opsoclonus • Chaotic saccades occuring randomly in any

direction• Aka saccadomania

• Causes – cerebellar disease , post viral encephalopathy , paraneoplastic sign , drug toxicity

• Internuclear ophthalmoplegia• Lesion of the MLF

• INO is named for the side of the MLF lesion• Posterior INO – convergence is preserved• Anterior INO – absence of convergence• WEBINO – bilateral INO• Myaesthenia can present similarly – pseudo

INO

• One and a half syndrome – PPRF lesion plus ipsilateral MLF lesion

• Only movement left is contralateral abduction

• “Paralytic pontine exotropia”- transient phenomenon seen during first few days of one and a half syndrome – due to unopposed action of contralateral PPRF

DISORDERS OF VERTICAL GAZE

• Downgaze palsy – • Occlusion of posterior thalamo-subthalmic

artery which enters from anterior part of midbrain (Percheron's artery),

• Upgaze palsy – lesion in rostral midbrain (posterior comissure)

• Dorsal midbrain syndrome• Aka Parinauds syndrome / Sylvian aqueduct

syndrome• Paresis of vertical gaze –mainly upward• Light near dissociation of pupils• Convergence retraction nystagmus• Lid retraction – Colliers sign• Spasm / paresis of convergence• Spasm / paresis of accomodation

• Skew deviation• Acquired vertical and torsional deviation• May be comintant or incomitant• Due to imbalance of otolithic inputs from

utricule and saccule to ocular motor neurons• With lower brainstem lesions the ipsilateral

eye tends to be hypotropic , with pontine and midbrain lesions the eye tends to be hypertropic

• Ocular tilt reaction• Due to lesion affection central or peripheral

otolithic pathways

• Destructive lesion of INC leads to :• Contralateral head tilt• Depression and extorsion of contralateral eye• Elevation and intortion of ipsilateral eye

• 4th nerve palsy extortion of hypertropic eye• OTR intortion of hypertropic eye

• Tonic downward deviation of gaze, or forced downgaze, is associated with medial thalamic hemorrhage, acute obstructive hydrocephalus, severe metabolic or hypoxic encephalopathy, or massive subarachnoid hemorrhage.

• When associated with lid retraction, the corneas can be buried below the lower lid (sundowning).

• In this setting, elevated intracranial pressure is a major concern.