Acquired Nystagmus Flashcards
what is nystagmus
an involuntary rythmic oscillation of one or both eyes
direction can be horizontal vertical torsional or mixed
can be conjugate or disconguate
can be disscociated , only unilateral/bilateral
Conjugate (both eyes display same movement) or disconjugate (the eyes show different movements e.g. one eye has horizontal nystagmus and the other vertical nystagmus) eye movements may be observed.
Dissociated
nystagmus (nystagmus is of different amplitude between the two eyes) may also be noted in acquired nystagmus.
what type of nystagmus is acquired and disconjugate nystagmus more common in
acquired and disconjugate nystagmus is More common in in acquired cases
what is nystagmus a product of
product of the failure of the mechanisms which hold the eye steady
Nystagmus→ by failure to hold the eyes steady- slow phase= defective- pathway
Mechanisms to hold eyes steady:
Vestibular ocular reflex (VOR) – steady gaze when head moving
Optokinetic & smooth pursuit systems
Separate ‘fixation system’
Neural integrator (holds the eyes steady in eccentric gaze)
when systems break down causes nystagmus
Vestibular-ocular reflex (VOR) –reflex eye movements that hold images of the seen world steady on the retina during brief head rotation.
Optokinetic and smooth pursuit system – theses eye movements are produced in response to retinal image slip.
Fixation system – – ability to detect retinal image slip and programme corrective eye movements, and the ability to suppress unwanted saccades that would take the eye away from target
Gaze-holding system (neural integrator) – is a network of neurones required to hold the eyes in eccentric gaze. A constant level of fine-tuning of muscle activity is needed to counteract the elastic pull of the extraocular structures (eg fat, muscles), which would tend to return the eye toward a central position in the orbit.
If any of the above described mechanisms which normally act to hold the eyes steady malfunction, nystagmus may develop.
what is phsyiological nystagmus
Induced by
self-rotation
instilling water into ear (vestibular nystagmus)
Fine end-point nystagmus- when pt gets to end of restriction
Differentiate from pathological gaze-evoked nystagmus
A considerable number of normal individuals display a fine jerky nystagmus on extreme gaze and is described as end-point nystagmus
describe the waveforms produced in acquired nystagmus
The waveforms can be pendular, jerk, or a combination of the two.
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).
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.
For a brief period of time the target is held on the fovea, which is termed the foveation period.
It is generally agreed that the slow phase resembles the pathology.
The amplitude is measured in degrees, and is defined as the peak-to-trough of the waveform.
The frequency is measured in Hertz, and is defined as the number of oscillations per second.
The Nystagmus Intensity is given by multiplying the amplitude and frequency.
how are the different types of acquired nystagmus categorised
can be separated into conjugate and diconjugate
what are the different types of acquired conjugate nystagmus
conjugate acquired nystagmus
- gaze evoked nystagmus
- periodic alternating nystagmus
peripheral vestibular nystagmus
central vestibular (upbeat nystagmus and downbeat nystagmus)
what are the different types of disconugate nystagmus
acquired pendular nystagmus
internuclear ophthalmoplegia
see saw nystagmus
convergence retraction nystagmus
describe the features of acquired pendular nystagmus
Pendular nystagmus is a to-&-fro oscillation of the eyes
Optic pathway glioma – monocular((uniocular) nystagmus may be the presenting sign in young children< 2 years (Toledano et al 2015)
what is acquired nystagmus without complaints of oscillopisa suggest
associated with anterior visual pathway defects or brainstem lesions
what is acquired pendular nystagmus associated with
Visual loss
Aetiology: trauma, retinal or optic nerve disease
Large amplitude, often vertical, maybe uniocular
Multiple Sclerosis (MS)
Disconjugate & dissociated
C/o disabling oscillopsia
See-saw nystagmus
Aetiology: lesion of optic chiasm, brainstem disease, advanced retinitis pigmentosa
1 eye rise & intort while the other eye falls & extort
what conditions are acquired pendular nystagmus associated with
Spasmus Nutans
Aetiology unknown
Onset before 18 months old
Triad of nystagmus, head nodding & torticollis
Nystagmus: rapid, pendular dissociated low amp oscillation
Nystagmus may ↓ with head nodding
Resolves clinically by ~5 years
Oculopalatal tremor (myoclonus)
Aetiology: pontomedullary infarct/ haemorrhage
Synchronised ocular & palatal oscillations- also have jaw movements – caused by haemhorrhage
describe how acquired jerk nystagmus induced by vestibular disease disease caused peripheral imbalance
defective Slow phase → corrective fast phase
Induced by Vestibular System Disease
Peripheral Imbalance
Aetiology: disease affecting vestibular organ e.g. labyrinthitis → R-L imbalance
Mixed horizontal-torsional nystagmus
Slow phase towards affected side
Fall towards affected side
VOR abnormal/ absent
C/o oscillopsia, nausea, vertigo, dizziness
describe how acquired jerk nystagmus induced by vestibulr system disease caused central imbalance issues
Central Imbalance
Vestibular imbalance → by cerebellar or medulla lesions
Down-beat Nystagmus
Fast phase down in all positions
↑ on down-gaze & often lateral gaze
Aetiology: cerebellar degeneration, cerebellar ischaemia, Arnold-Chiari malformation, drug intoxication (e.g. anticonvulsants & lithium)
Other mechanisms:
Imbalance of vertical smooth-pursuit → spontaneous upward drift
Mismatch for vertical saccade generation
how does acquired jerk nystagmus induced by vestibular system disease causes up beat nystagmus issues
Up-beat Nystagmus
Fast phase up in all positions
↑ on up-gaze
Associated with impaired vertical smooth pursuit
Aetiology: MS, brainstem tumour/ stroke, Wernicke’s encephalopathy, cerebellar degeneration, drug intoxication
Other mechanisms:
Imbalance of vertical VOR
Mismatch of saccadic generation & velocity-to-position integration
