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Showing posts with label Nystagmus. Show all posts
Showing posts with label Nystagmus. Show all posts

What is See-Saw Nystagmus?

What is See-Saw Nystagmus?

In see-saw nystagmus one eye moves up + intorts & other eye moves down +extorts

Torsional component is conjugate

Vertical component is dysconjugate

1. Wave form is pendular or jerk

What are the types of See-Saw Nystagmus?

Pendular see-saw nystagmus

Seen in

  1. Suprasellar lesion
  2. Visual loss
  3. Joubert's syndrome

Jerk see-saw nystagmus: (Hemi see-saw nystagmus)

Half cycle is pendular with corrective half cycle jerky

Seen in

  1. lesions of INC (caudal thalamus-rostral midbrain)

See-Saw Nystagmus Pathogenesis:

Midbrain

Unilateral inactivation of INC

Sparing of riMLF

Afferent

  1. Bitemporal hemianopia.
  2. Visual loss-visuo-vestibular fibres
  3. Chiasmal miswiring

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What are the causes of Acquired Pendular nystagmus ?

What are the causes of Acquired Pendular nystagmus ?

  1. Acquired Pendular nystagmus can be seen in the following conditions
  2. Oculo-palatal myoclonus
  3. See-saw nystagmus
  4. Oculomasticatory myorhythmia
  5. Visual loss
  6. Spasmus nutans

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What is Convergence-Retraction Nystagmus?

Convergence-Retraction Nystagmus is characterised by rapid convergence with synchronous

retraction of both globes slow divergence.

It is due simultaneous contraction of all EOM

This is best detected by:

  1. Looking up
  2. OKN

What is the site of lesion in convergence retraction nystagmus

Dorsal midbrain


Reference Notes 

What is See-Saw Nystagmus ?
What are the causes of Acquired Pendular nystagmus ?
What is Convergence-Retraction Nystagmus ?
Dissociated Jerk Nystagmus and causes
What is Rebound nystagmus and its causes?
What is Bruns's nystagmus?
What is Gaze evoked nystagmus?
Down-beat nystagmus and its causes
Upbeat nystagmus and its causes
What is the basic Pathophysiology of Nystagmus
Alexanders law in Nystagmus - A brief

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Dissociated Jerk Nystagmus and causes

Dissociated Jerk Nystagmus and causes

Dissociated Jerk Nystagmus and causes

Dissociated Jerk Nystagmus ,nystagmus is different in both eyes

INO (Internuclear ophthalmoplegia)

Ipsilateral adduction deficit with contralateral abduction nystagmus

Vertical nystagmus can occur in INO

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What is Rebound nystagmus and its causes?

 Rebound nystagmus is a Gaze evoked nystagmus reverses direction in the eccentric gaze.

  • In Primary position - No nystagmus
  • Lateral gaze - Initiates nystagmus

        On return from lateral gaze, nystagmus reverses direction.
        Occasionally reverses direction while maintaining prolonged lateral gaze.

What are the causes of Rebound nystagmus?

It is seen in

  1. Cerebellar disorder
  2. Medullary lesion
  3. Lesions of NPH

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What is Bruns's nystagmus?

It is seen in large CP angle tumours

Following are the components of Bruns nystagmus.

Contralateral high frequency / low amplitude nystagmus

This is due to Peripheral vestibular affection

Ipsilateral high amplitude nystagmus

This is due to affection of neural integrator from brain stem compression


Reference Notes 

What is See-Saw Nystagmus ?
What are the causes of Acquired Pendular nystagmus ?
What is Convergence-Retraction Nystagmus ?
Dissociated Jerk Nystagmus and causes
What is Rebound nystagmus and its causes?
What is Bruns's nystagmus?
What is Gaze evoked nystagmus?
Down-beat nystagmus and its causes
Upbeat nystagmus and its causes
What is the basic Pathophysiology of Nystagmus
Alexanders law in Nystagmus - A brief

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What is Gaze evoked nystagmus?

Gaze holding helps to maintain eye in the eccentric eye position.

This is done with the help of the Pulse-step innervation



When the eye moves towards the corner and if the neural integrator is perfect the viscous drag is overcome by the pulse and made to stay in the extremes of gaze by the step.

And if the neural integrator is leaky eye moves and from there due to leaky potential it moves

towards the central.

What are the causes of Gaze evoked nystagmus ?

1. Due to leaky neural integrator

Lesion of Nucleus prepositus hypoglossi/ Medial Vestibular Nuclei

  • Horizontal gaze evoked nystagmus
  • Direction changing nystagmus
  • Fast component is the direction of fixation

Bilateral lesion of INC

  • Impaired vertical gaze holding

2. Lesions of vestibulo-cerebellum

What are the types of Gaze evoked nystagmus?

  • Symmetrical gaze evoked nystagmus

Anticonvulsants, particularly phenytoin and phenobarbitone, and ingestion of psychotropic drugs and alcohol.

  •          Asymmetrical gaze evoked nystagmus

Affecting the brain stem /flocculonodular lobe

Reference Notes 

What is See-Saw Nystagmus ?
What are the causes of Acquired Pendular nystagmus ?
What is Convergence-Retraction Nystagmus ?
Dissociated Jerk Nystagmus and causes
What is Rebound nystagmus and its causes?
What is Bruns's nystagmus?
What is Gaze evoked nystagmus?
Down-beat nystagmus and its causes
Upbeat nystagmus and its causes
What is the basic Pathophysiology of Nystagmus
Alexanders law in Nystagmus - A brief


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Down-beat nystagmus and its causes

Down-beat nystagmus is a central vestibular disorders -Pitch plane disorder.

It is a Jerk nystagmus with fast phase downwards.

Most prominent on looking down & out.

What is the site of lesion in downbeat nystagmus?

Site of lesion in down gaze nystagmus is disruption of posterior SCC projections secondary to Lesions

in the floor of fourth ventricle.

  • Bilateral lesions of the flocculi

What are the causes of Downbeat nystagmus?

  1. Lesions of cervico-medullary junction - ACM.
  2. Lesions of flocculus, paraflocculus, nodule, uvula & medulla.
  3. Spinocerebellar ataxia.
  4. Metabolic causes.
    Wernicke's encephalopathy.
    Deficiency of magnesium, thiamine, Vit B12.
  1. Toxic.
    Lithium, Phenytoin, CBZ, morphine, amiodarone.
    Alcohol intoxication.

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Upbeat nystagmus and its causes

Upgaze nystagmus is a  Central vestibular disorders -Pitch plane disorder

  • Nystagmus with fast phase upwards in primary position it  worsens on upward gaze

Where is the site of lesion?

  • The site of lesion is Tegmentum of the pontomesencephalic region (either the SCP orVTT) 

SCP - superior cerebellar peduncle or VTT - vestibulotegmental tract.

  • Pontomedullary junction (NPH)

What are the causes of Upbeat nystagmus ?

  • CVD, MS.
  • Cerebellar degeneration.
  • Wernicke's encephalopathy
  • Encephalitis
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What is the basic Pathophysiology of Nystagmus

Nystagmus is a Disorder of ocular posture / mechanisms that maintain steady fixation.

The Basic pathology is the abnormality in gaze stabilizing mechanism

There are three main mechanism which will maintain the image of the object steady on the retina

and preserve the visual acuity they are

  1. Visual Fixation mechanism
  2. Vestibulo-ocular reflex
  3. Gaze Holding mechanism

Any abnormality will lead to disorder of slow eye movement resulting in Nystagmus


Reference Notes 

What is See-Saw Nystagmus ?
What are the causes of Acquired Pendular nystagmus ?
What is Convergence-Retraction Nystagmus ?
Dissociated Jerk Nystagmus and causes
What is Rebound nystagmus and its causes?
What is Bruns's nystagmus?
What is Gaze evoked nystagmus?
Down-beat nystagmus and its causes
Upbeat nystagmus and its causes
What is the basic Pathophysiology of Nystagmus
Alexanders law in Nystagmus - A brief

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