Nystagmus is a series of involuntary, rhythmic oscillations of one or both eyes. It may be horizontal, vertical or rotatory.
What is pendular nystagmus?
In pendular nystagmus, the oscillations are equal in speed and amplitude in both directions of movement. It may be seen on central gaze when the vision is poor, as in severe refractive error or macular disease.
What do you understand by the term 'jerky' nystagmus?
Jerky or phasic nystagmus is a condition in which eye movement in one direction is faster than that in the other. This is usually seen in the horizontal plane and is brought out by lateral gaze to one or both sides. It is seen with lesions of the cerebellum, vestibular
apparatus or their connections in the brainstem.
What is dissociated nystagmus?
Dissociated or ataxic nystagmus is irregular nystagmus in the abducting eye. It is bilateral in multiple sclerosis, brainstem tumour or Wernicke's encephalopathy. It is unilateral in vascular disease of the brainstem. It is due to a lesion in the medial longitudinal fasciculus (which links the sixth nerve nucleus on one side to the medial rectus portion of the third nerve on the other).
Where is the lesion in vestibular nystagmus?
It may be in one of two locations:
· Peripheral (labyrinth or vestibular nerve), as in labyrinthitis, Meniere's syn-drome, acoustic neuroma, otitis media, head injury.
· Central (affecting vestibular nuclei), as in stroke, multiple sclerosis, tumours, alcoholism.
What do you know about 'downbeat' and 'upbeat' nystagmus?
Downbeat nystagmus is associated with brainstem lesions, meningoencephalitis and hypomagnesaemia. Upbeat nystagmus is caused by lesions of the anterior vermis of the cerebellum.
0 comments:
Post a Comment