Nystagmus is an involuntary, rapid and repetitive movement of the eyes. Usually, the movement is side-to-side (horizontal nystagmus), but it can also be up and down (vertical nystagmus) or circular (rotary nystagmus). The movement can vary between slow and fast, and it usually involves both eyes.
- Down/upbeat: CNS dysfunction
- Vestibular (horizontal): labyrinth or vestibular nerve dysfunction
- Gaze-evoked: most common and often benign
There are two types of nystagmus: congenital and acquired:
- Congenital nystagmus develops in infancy, usually between six weeks and three months of age. Sensory nystagmus also occurs early in life and is related to poor vision caused by a variety of eye conditions, including cataract (cloudiness of the eye's lens), strabismus (eye misalignment) and optic nerve hypoplasia. As they get older, children with nystagmus don't see the world as shaky, but they will probably develop less clear vision.
- Acquired nystagmus occurs later in life and has a variety of causes, including an association with serious medical conditions. Unlike children with nystagmus, adults who acquire nystagmus may see images as shaky.
Nystagmus is very noticeable but rarely recognized.
Nystagmus can be clinically investigated by using a number of non-invasive standard tests.
The simplest one is the caloric reflex test, in which one ear canal is irrigated with warm or cold water or air. The temperature gradient provokes the stimulation of the horizontal semicircular canal and the consequent nystagmus. Nystagmus is often very commonly present with Chiari malformation.
The resulting movement of the eyes may be recorded and quantified by special devices called electronystagmograph (ENG), a form of electrooculography (an electrical method of measuring eye movements using external electrodes), or even less invasive devices called videonystagmograph (VNG), a form of video-oculography (VOG) (a video-based method of measuring eye movements using external small cameras built into head masks) by an audiologist. Special swinging chairs with electrical controls can be used to induce rotatory nystagmus.
Orthoptists may also use an optokinetic drum, or electrooculography to assess a patient's eye movements.
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.
Several therapeutic approaches, such as contact lenses, drugs, surgery, and low vision rehabilitation have also been proposed. For example it has been proposed that mini-telescopic eyeglasses suppress nystagmus.
Surgical treatment of Congenital Nystagmus is aimed at improving the abnormal head posture, simulating artificial divergence or weakening the horizontal recti muscles. Clinical trials of a surgery to treat nystagmus (known as tenotomy) concluded in 2001. Tenotomy is now being performed regularly at numerous centres around the world. The surgery developed by Louis F. Dell'Osso Ph.D. aims to reduce the eye shaking (oscillations), which in turn tends to improve visual acuity.
Acupuncture has conflicting evidence as to having beneficial effects on the symptoms of nystagmus. Benefits have been seen in treatments where acupuncture points of the neck were used, specifically points on the sternocleidomastoid muscle.
Benefits of acupuncture for treatment of nystagmus include a reduction in frequency and decreased slow phase velocities which led to an increase in foveation duration periods both during and after treatment. By the standards of Evidence-based medicine, the quality of these studies can be considered poor.
Physical therapy or Occupational therapy is also used to treat nystagmus. Treatment consist of learning compensatory strategies to take over for the impaired system.
central nervous system (CNS) lesion
Central lesions often have dissociation of the vertigo and nystagmus. The nystagmus in this condition is often vertical and without fatigability with repeated testing.
acute cocaine toxicity