Acquired nystagmus Flashcards
What is acquired nystagmus
an involuntary rhythmic oscillation of one or both eyes.
What direction can nystagmus be
horizontal, vertical, torsional and mixed. Also, it can be conjugate or deconjugate and it is also dissociated (different amplitude within eyes).
What causes gaze holding nystagmus
Failure to hold the eyes steady leads to NYSTAGMUS
What mechanisms are used to hold the eyes steady
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Vestibular ocular reflex (VOR) – reflex eye movements that all steady gaze when head moving
Optokinetic & smooth pursuit systems
Neural integrator – network of neurones that holds the eyes steady in eccentric gaze
What is a phsyological nystagmus
It is induced by self-rotation and instilling water into the ear (vestibular nystagmus). The normal type of nystagmus is fine end point.
What induces physiological nystagmus
and types
Physiological nystagmus such as optokinetic and vestibular nystagmus can be induced by self rotation or instilling water into the ear.
What is end point nystagmus
a fine jerky nystagmus on extreme gaze
What is pendular nystagmus
consists of 2 slow phases, where the eyes oscillate (swing) from one side to the other. When the sinusoid is at its right or left turning point, the retinal image of a target is placed at the fovea. (and the eye velocity is minimum).
What is jerk nystagmus
consists of a slow phase, in which the eyes drift and takes the target off the fovea, followed by a corrective fast phase, which brings the target back to fovea.
What is the foveation period
a brief period of time the target is held on the fovea
Does the slow phase resemeble pathology
generally, yes
What is meant by nystagmus amplitude
measured in degrees, and is defined as the peak-to-trough of the waveform.
What is meant by nystagmys frequency
measured in Hertz, and is defined as the number of oscillations per second.
What is meant by nystagmus intensity
by multiplying the amplitude and frequency.
Classification acquired nystagmus
1- physiological, early onset, acquired.
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2- conjugate, diconjugate
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3-conjugate - gaze evoked nystagmus, periodic alternatinating nystagmus, peripheral vestibular, central vestibular
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Upbeat, downbeat
4- disconjuate- acquired pendular, INO, see-saw, convergence retraction
What is acquired pendular nystagmus
It causes a to-&-fro sinusoidal oscillation of the eyes. The direction can be horizontal, vertical or torsional.
What is acquired pendular nystagmus associated with
anterior visual pathway defect (e.g OPG), brainstem lesions, MS, trauma, retinal or optic nerve problems
More on acquired pendular nystagmus
When binocular it can be disconjugate & dissociated however when it is uniocular: Heimann-Bielschowsky Phenomenon (an unusual dissociated nystagmus which may develop years following uniocular visual loss). If there is no oscillopsia (remember only acquired have oscillopsia).
Features of spasmus nutans
- Triad of nystagmus, head nodding & torticollis
- Nystagmus: rapid, pendular dissociated low amp oscillation
- Nystagmus may ↓ with head nodding
Prognosis and aetiology of spasmus nutans
- Aetiology unknown – acquired?
- Onset before 18 months old
- Resolves clinically by ~5 years
Aetiology and features of oculoplatal tremor (myoclonus)
- Aetiology: pontomedullary infarct/ haemorrhage
- Synchronised ocular & palatal oscillations
What is acquired jerk nystagmus
There is a slow phase followed by a fast corrective phase. It is induced by vestibular system disease. It causes a peripheral imbalance. The aetiology is a disease affecting the vestibular organ e.g. labyrinthitis → R-L imbalance.
What can acquired jerk nystagmus cause
Mixed horizontal-torsional nystagmus
Slow phase towards affected side
Fall towards affected side
VOR abnormal/ absent
C/o oscillopsia, nausea, vertigo, dizziness
What is acquired jerk nystagmus caused by
vestibular system disease
