Definition of nystagmus: it is an involuntary movement of the eye (it is voluntary in very rare cases) that leads to the deviation of the eyes away from the field of vision and then the eye returns to the central resting position and it is acquired in early childhood or any age stages.
It is also called "dancing eye" disease. Nystagmus can be rapid, slow, or a mixture of both, and it can be continuous or intermittent with postural stimuli (influenced by changing the position of the head).
Classification and types:
a. Physiologic (optokinetic): the rapid phase is towards the center.
- Occular: rotatory or pendular.
- Vestibular: has a rapid phase and a slow phase.
- Central: vertical.
Causes of nystagmus
Nystagmus in newborns often appears three months after birth and its movement is transverse and is associated with some other disorders such as albinism, absence of the iris of the eye, congenital cataracts and poor development of the optic nerve.
Children from the age of 6 months to 3 years develop a special type of nystagmus, which is automatically relieved without therapeutic interventions between the ages of 2-8 years.
Acquired (non-congenital) causes of nystagmus should be sought if the nystagmus appears later than the eye has been normal.
Other causes and contributing factors to the occurrence of nystagmus include:
- The immaturity and delayed development of the natural eye movement of the fetus in the womb or in its first months after birth for unknown aetiology
- Severe degrees of errors of refraction such as myopia and astigmatism
- Congenital cataract
- Inner ear infection
- Taking antiepileptic drugs
- Certain diseases of the central nervous system (diseases of the brain and spinal cord)
Symptoms of nystagmus
Common symptoms associated with nystagmus include:
- Involuntary eye movements
- Movements can be in one eye or in both eyes
- The patient sees things shaky or unclear
- light sensitivity
- Difficulty seeing at night
- Dizziness and loss of balance
Signs of nystagmus
The doctor can diagnose nystagmus and determine its type in the following ways:
- Observation of nystagmus theoretically by looking into the affected eye.
- Detection by Frenzel glasses to remove the effect of optical stabilization.
- Electromyography and videography.
Detection and diagnosis of Nystagmus
a. Direct observation by looking into the eyes.
b. Observation using Frenzel glasses to abolish the optic fixation.
c. Electronystagmography and videonystagmography.
A. Positional testing and search for any nystagmus (central or peripheral) in:
i. Static head and body position tests (supine - head right- head left - body right - body left).
ii. Dynamic (positioning tests) for diagnosis of BPPV:
- Dix-Hallpike test
- Roll test.
B. Sound stimuli, the Valsalva maneuver, and tragal compression to test Tullio phenomenon
C. The Vestibulo-Ocular Reflex testing (VOR)
- Horizontal Head impulse test (hHIT)
- Dynamic visual acuity test (DVA)
D. Clinical oculography test: Saccades, smooth pursuit and optokinetic testing (rotating drum test).
Vestibular investigations to diagnose Nystagmus
1. Video-nystagmography (VNG): A video of the eye that could be recorded
- The caloric test is performed with the subject reclining, head inclined 30 degree up from horizontal so as to make the lateral canal horizontal.
- Bi-thermal caloric test stimulates the left or right ear with warm and cool air or water causing a fluid density change in the lateral canal.
- Water is introduced into the ear canal on one side, either 7 deg centigrade above or below assumed body temperature.
- The flow rate is such that the ear rapidly equilibrates with the water. The water is stopped after 30 seconds, and nystagmus is observed, while the subject is distracted.
- Eye movements are usually recorded, and by comparing the response of the left and right ear to warm and cool stimuli one can determine if there is a unilateral or bilateral weakness.
and search for any nystagmus and determine whether central or peripheral, as in clinical testing.
- Saccades testing: re-fixation on new targets
- Smooth Pursuit: tacking slow objects with foveal vision
- Optokinetic test: sensing objects with peripheral vision
Determining the presence or absence of spontaneous or Gaze evoked nystagmus
2. Computerized dynamic Posturography (CDP):
- Postural sway has been used as an indicator of balance function.
- It can be recorded by force platform Posturography that measures forces needed to maintain the balance and support the body weight while standing on the platform.
3. Rotatory chair testing:
- The rotational chair has primarily been used for analyzing horizontal canal vestibulo-ocular reflex (VOR).
- Angular acceleration stimulus to test VOR. Both sides are stimulated simultaneously.
- It is the Gold-standard test for Bilateral vestibular loss
- Useful to validate caloric paresis.
Audiologic: PTA, Speech audiometry, Tympanometry, ABR, and OAE.
Laboratory: CBC including Hb %., blood lipid profile, Blood glucose level, Thyroid function tests, and Syphilis serology.
Radiological: -CT scan Bain, brainstem and cerebellum -MRI Bain, brainstem and cerebellum.