In practice, we see the pupil moving in one direction and then another involuntarily and with the same frequency. The movement resembles that of a pendulum.

The movement can be:

  • Induced,
  • Brought about,
  • Spontaneous.

The eyes can move:

  • In laterality (horizontal nystagmus),
  • Moving up and down (vertical nystagmus),
  • They can perform a rotation.

Nystagmus is often evident when one looks fixedly at an object present in peripheral vision or when one observes moving objects with a very high velocity.

In most cases, nystagmus appears during childhood or adolescence, but may develop in adulthood. 
Experts say that about one child in a thousand has nystagmus.

The rhythm of eye movements can be subdivided into slow and fast.

  1. The slow phase is physiologically or pathologically induced by a vestibular stimulus.
  2. The rapid phase is a rapid movement induced by the oculomotor system that controls the movements of the eyes.

 

Types of nystagmus

Pathological
nystagmus A pathological nystagmus occurs during a rotation of the trunk relative to the head, which is stopped in space; in this case the disorder comes from the cervical vertebral column . 
This cervical nystagmus may have:

  1. vascular origin due to compression of the vertebral arteries,
  2. proprioceptive origin  (ability to perceive the position of the body in space) of the joints of the neck,
  3. It is caused by functional disturbances of the upper cervical spine .

Physiological  nystagmus : Physiological nystagmus preserves clear vision during autorotation. 
In many cases, for example during locomotion, the movements of the head are small and the vestibulo-ocular reflex is able to generate a compensatory movement of the eyes.

There are some types of physiological nystagmus:

  • The optokinetic nystagmus is a physiological response of the eye muscles that is looking for objects in motion (eg, looking out the train window). 
    The eye makes a slow movement to follow the object and then jumps back to observe another object. 
    It is a physiological nystagmus that appears early in life; in some cases, a few weeks after birth.
  • The buccal nystagmus (connected to the inner ear). 
    The vestibular system works in conjunction with the oculomotor system. 
    If the ear receives specific stimuli (for example, passive rotation of the head), the eyes move rhythmically and thus nystagmus occurs. 
    If communication between the two systems is not adequate, nystagmus may occur. 
    Vestibular nystagmus consists of involuntary eye movements due to an inner ear disorder (eg, tinnitus or hearing loss ). 
    This nystagmus is divided into:

1. Central vestibular nystagmus , in this case the ocular movement can be in one or both directions; 
2. Peripheral vestibular nystagmus , eye movement is always in the same direction.

 

Classification  of nystagmus

Nystagmus may be congenital (present at birth) or acquired due to injury or disease.

Congenital nystagmus

Childhood nystagmus syndrome (INS)

Appearance: 0-6 months old

Nystagmus at this age may be:

  1. Congenital idiopathic nystagmus (CIN): 
    Newborns have a nystagmus in all positions of the gaze, but the eyes and motor development are clinically normal. 
    This diagnosis is made only when all neurological and ocular anomalies have been excluded.
  2. Cogan Sensory Nystagmus
    It is linked to eye diseases that affect both eyes and cause a deficit in the development of visual fixation and reduced visual acuity.

A child with sensory deficiencies in vision or oculomotor disorders may not suffer from nystagmus.

 

Acquired nystagmus

Acquired nystagmus may be caused by

Hyperventilation, a blinking light in front of the eye, nicotine and vibrations can cause nystagmus in rare cases. 
Some cases of acquired nystagmus can be treated with medication or surgery.

Spasmus nutans
This syndrome is characterized by the presence of nystagmus, oscillations and abnormal head positions ( torticollis ).

Bounce nystagmus : This nystagmus occurs by keeping the eyes away from the midline of the body. 
This form is caused by brain stem dysfunction or sedative drugs. 
Nystagmus may worsen when the person is tired or stressed, or when he or she stares in the peripheral direction.

Retractable nystagmus to convergence
This is a provoked nystagmus that occurs in the case of dorsal midbrain lesions (eg Parinaud syndrome or pinealoma). 
The eyeballs

  • converge towards the center at the same time
  • and then return to the starting position.

Retractable nystagmus to ocular convergence occurs when the patient attempts the elevation movement of the ocular globe that is reduced or paralyzed.

Opsoclonus (dancing eyes):  opsoclonus is not a true nystagmus, but a rapid oscillation in high frequency, low amplitude and unintentional. It is often called “dancing eyes and dancing feet” because of its association with acute cerebellar ataxia in childhood. 
Opsoclonus may be a sign of neuroblastoma.

 

Classification of nystagmus based on the situation

  • Monocular (unilateral) or bilateral nystagmus: may involve one or both eyes .
  • Voluntary nystagmus: Some people can create nystagmus voluntarily. Rapid and horizontal movements can be produced and maintained for short periods of time.
  • Nystagmus of the miner: This form of nystagmus occurs in those who work in the dark for long periods.
  • Balance nystagmus: in this case the eyes make opposite movements, while one rises the other descends.
  • Spontaneous and induced nystagmus: this form of nystagmus occurs randomly, without considering the position of the head.
  • Manifest nystagmus: it is present at all times, while that latent occurs when an eye is covered.
  • A latent manifest nystagmus: it is always present, but it worsens when the eye is covered.
  • Fixation nystagmus : occurs only when the eyes fix an object.
  • Dissociated nystagmus:  the manifestation in one eye is not synchronized with that of the other eye.

 

Classification of nystagmus based on movements

  • Pendular nystagmus: The speed of eye movement is the same in both directions.
  • Jerk jerking or jerking nystagmus: eyes slowly move in one direction and then back quickly.
  • Sacadic or biphasic nystagmus: velocity is different as a function of direction. 
    The fast component (rapid phase) gives the name to the direction of nystagmus (saccade nystagmus to the left has the slow phase to the right and the fast to the left).
  • Lateral nystagmus: The eyes move with horizontal muscle contractions (side to side).
  • Rotatory or torsional nystagmus: the eyes revolve around the visual axis.
  • Post rotational nystagmus: this is a form of vestibular nystagmus and occurs when the whole body is rotated and then to. 
    For example, when someone turns around a chair and stops suddenly.
  • Geotropic nystagmus worsens during rotation to the affected side. 
    Apogeotropic nystagmus gets  worse when the head turns to the healthy side.

 

Symmetrical vertical nystagmus

  • Vertical Nystagmus Up :
    Description – This is a saccadic nystagmus in which the rapid phase goes up. 
    Appears in the primary position of the look and increases looking up. 
    Associated diseases – it is often seen as side effects of anticonvulsants, but can also occur in cerebellar and spinal disorders.
  • Vertical downward nystagmus :
    Description – This saccadic nystagmus has a rapid descending phase that is present in the primary position but worsens looking down. 
    Associated Diseases: There are several causes, including:
  • Anomalies at the craniocervical junction (eg, Arnold-Chiari syndrome ),
  • Cerebellar degeneration,
  • Drug intoxication (especially with lithium, phenytoin , carbamazepine and barbiturates),
  • Encephalopathy by Wernicke,
  • Desmielinização,
  • Brain stem encephalitis and hydrocephalus.

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