Nystagmus

Nystagmus can be caused by subsequent foveation of moving objects, pathology, sustained rotation, or substance abuse.

The direction of nystagmus is defined by the direction of its quick phase (e.g. a right-beating nystagmus is characterized by a rightward-moving quick phase). The oscillations may occur in the vertical, horizontal or torsional planes, or in any combination. The resulting nystagmus is often named as a gross description of the movement, e.g. downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus.

These descriptive names can be misleading however, as many were assigned historically, solely on the basis of subjective clinical examination, which is not sufficient to determine the eyes' true trajectory.

Over the past forty years, however, objective eye movement recording techniques have been applied to the study of nystagmus, and the results have led to a greater accuracy and understanding of the condition.

Nystagmus is not to be confused with other superficially similar-appearing disorders of eye movements (saccadic oscillations) such as opsoclonus or ocular flutter that are composed purely of fast-phase (saccadic) eye movements, while nystagmus is characterised by the combination of a smooth pursuit, which usually acts to take the eye off the point of regard, interspersed with the saccadic movement that serves to bring the eye back on target. Without the use of objective recording techniques, it may be very difficult to distinguish between these conditions.

In medicine, the presence of nystagmus can be benign, or it can indicate an underlying visual or neurological problem. Over forty types of nystagmus have been classified.[citation needed]


[edit] Nystagmus and alcohol
In police work, testing for horizontal gaze nystagmus is one of a battery of field sobriety tests used by officers in the field to determine whether a suspect is driving under the influence of alcohol. The test involves observation of the suspect's pupil as it follows a moving object, noting (1) lack of smooth pursuit, (2) distinct and sustained nystagmus at maximum deviation, and (3) the onset of nystagmus prior to 45 degrees. A general rule of thumb is that a person's blood alcohol concentration can be estimated by subtracting the angle of onset from 50 degrees. Therefore, a person with an angle of onset of nystagmus at 35 degrees has a blood alcohol concentration of approximately 0.15%. Unfortunately, due to the complexities of eye conditions and physiology, police (with very limited ophthalmologic training) may be unable to disguish horizontal gaze nystagmus from other conditions such as occular flutter.


[edit] Pathological nystagmus
When nystagmus occurs without filling its normal function, then it's pathologic (deviating from the healthy or normal condition).

Pathological nystagmus generally causes a degree of vision impairment, although the severity of such impairment varies widely. Sometimes it is the other way round — many blind people have nystagmus, which is one reason that some wear dark glasses.[1]


[edit] Prevalence
Nystagmus is a relatively common clinical condition, affecting one in every 5,000 to 10,000 individuals.[citation needed] One survey in Oxfordshire, England identified one in every 670 children by the age of two as manifesting nystagmus. [2]


[edit] Variations
Vestibular nystagmus usually combines a rotational component with vertical or horizontal eye movements and may be spontaneous or positional.
Spontaneous vestibular nystagmus is nystagmus that occurs randomly, regardless of the position of the patient's head.
Positional nystagmus is different from spontaneous nystagmus in that it occurs when a persons head is in a specific position (e.g., Benign paroxysmal positional vertigo; BPPV). (See a video of Nystagmus associated with BPPV)

[edit] Causes
The cause for pathological nystagmus may be congenital, idiopathic, secondary to a pre-existing neurological disorder or may be induced temporarily by certain drugs (alcohol and other central nervous system depressants and stimulants, such as lithium salts, phenytoin and ecstasy).


[edit] Congenital
Congenital nystagmus occurs more frequently than acquired nystagmus, is not associated with other disorders (such as refraction errors or diplopia) and is usually mild and non-progressive. The affected persons are not aware of their spontaneous, small-amplitude eye movements.

Infantile:
Idiopathic
Albinism
Aniridia
Leber's congenital amaurosis
Bilateral optic nerve hypoplasia
Bilateral congenital cataracts
Rod monochromatism
Optic nerve or macular disease
Persistent hyperplastic primary vitreous
Latent nystagmus
Nystagmus blockage syndrome

[edit] Acquired

[edit] Diseases
Some of the diseases which present nystagmus as a pathological sign are:

Head trauma (the most common cause in young people)
Stroke (the most common cause in older people)
Ménière’s disease and other balance disorders
Multiple sclerosis
Brain tumors
Wernicke-Korsakoff syndrome
Encephalopathy
Lateral medullary syndrome
Aniridia
Optic nerve hypoplasia
Albinism
Noonan syndrome
Pelizaeus-Merzbacher disease

[edit] Visual loss
To this section count e.g.:

dense cataract
trauma
cone dystrophy

[edit] Toxic/metabolic
Nystagmus from toxic or metabolic reasons could be the result of e.g.:

alcohol intoxication
lithium
barbiturates
phenytoin(Dilantin)
salicylates
benzodiazepines
phencyclidine
other anticonvulsants or sedatives
Methylenedioxymethamphetamine
Wernicke's encephalopathy
thiamine deficiency

[edit] Central nervous system disorders
If the pathologic nystagmus is based in the central nervous system (CNS), such as with a cerebellar problem, the nystagmus can be in any direction including horizontal. Purely vertical nystagmus is usually central in origin.

Causes include e.g.:

Thalamic hemorrhage
Tumor
Stroke
Trauma
Multiple Sclerosis

[edit] Other causes
Vestibular Pathology (Ménière's disease, BPPV, Labyrinthitis)
Trochlear nerve malfunction[3]
Non-physiologic

[edit] Diagnosis
Nystagmus is very noticeable, but little recognised. Nystagmus can be clinically investigated by using a number of non-invasive standard tests. The simplest one is Caloric reflex test. In a caloric reflex test, one external auditory meatus is irrigated with warm or cold water. The temperature gradient provokes the stimulation of the vestibulocochlear nerve and the consequent nystagmus.

The resulting movement of the eyes may be recorded and quantified by special devices called electronystagmograph (ENG), which is a form of electrooculography (an electrical method of measuring eye movements using external electrodes) or even less invasive devices called videoonystagmograph (VNG), which is a form of videooculography(VOG) (a video-based method of measuring eye movements using external small cameras built into head masks). Special swinging chairs with electrical controls are also used in this test to induce rotatory nystagmus.


[edit] Treatment
Congenital nystagmus has traditionally been viewed as non-treatable, but medications have been discovered in recent years that show promise in some patients. In 1980, researchers discovered that a drug called baclofen could effectively stop periodic alternating nystagmus. Subsequently, gabapentin, an anticonvulsant, was found to cause improvement in about half the patients who received it to relieve symptoms of nystagmus. Other drugs found to be effective against nystagmus in some patients include memantine, levetiracetam, 3,4-diaminopyridine, 4-aminopyridine, and acetazolamide.[4] Several therapeutic approaches, such as contact lenses, drugs, surgery, and low vision rehabilitation can also be used in order to improve visual function.

This is what Christina suffers from since she was born.

Awwwwww how is she hun? x

She can never drive a car, cos of her concertration. She wears glasses all the time. She has had to cope with it as well.

awww bless her x

Will post some pics later