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Robbins & Cotran Pathologic Basis of Disease robbinspathology.com | Sepsis pathologic blood poisoning resulting optometry.com | Symposiums - Robbins and Cotran Pathologic Basis of Disease... scientificsymposiums.com |
Pathologic nystagmus is a form of involuntary eye movement. It is characterized by alternating smooth pursuit in one direction and saccadic movement in the other direction. When nystagmus occurs without filling its normal function, it is pathologic (deviating from the healthy or normal condition). Pathological nystagmus is the result of damage to one or more components of the vestibular system, including the semicircular canals, otolith organs, and the vestibulocerebellum. Pathological nystagmus generally causes a degree of vision impairment, although the severity of such impairment varies widely. Also, many blind people have nystagmus, which is one reason that some wear dark glasses.[1]
[edit] PrevalenceNystagmus 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 has manifesting nystagmus. [2] [edit] Variations
[edit] CausesThe cause for pathological nystagmus may be congenital, idiopathic, or secondary to a pre-existing neurological disorder; or it may be induced temporarily by disorientation (such as on roller coaster rides) or certain drugs (alcohol and other central nervous system depressants and stimulants, such as lithium salts, phenytoin, and MDMA). [edit] CongenitalCongenital nystagmus occurs more frequently than acquired nystagmus. It can be insular or accompany other disorders (such as micro-ophthalmic anomalies or Down's Syndrome). Congenital nystagmus itself is usually mild and non-progressive. The affected persons are not normally aware of their spontaneous eye movements but vision can be impaired depending on the severity of the movements.
X-linked infantile nystagmus is associated with FRMD7.[4] Congenital nystagmus is also associated with an X-linked eye disease known as Congenital Stationary Night Blindness (CSNB), which is caused at the genetic level by one of two genes located on the X chromosome, NYX and CACNA1F which are associated with CSNB 1 and CSNB 2 (two varieties of CSNB with differing symptoms and severity) respectively. [edit] Acquired[edit] DiseasesSome of the diseases that present nystagmus as a pathological sign:
[edit] Toxic/metabolicNystagmus from toxic or metabolic reasons could be the result of the following:
[edit] Central nervous system disordersIf 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.:
[edit] Other causes
[edit] DiagnosisNystagmus is very noticeable but little recognized. Nystagmus can be clinically investigated by using a number of non-invasive standard tests. The simplest one is Caloric reflex test, in which 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), a form of electrooculography (an electrical method of measuring eye movements using external electrodes), or even less invasive devices called videoonystagmograph (VNG), a form of videooculography(VOG) (a video-based method of measuring eye movements using external small cameras built into head masks) by an Audiologist or anOrthologist. Special swinging chairs with electrical controls are also used in this test to induce rotatory nystagmus. [edit] TreatmentCongenital 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[7], levetiracetam, 3,4-diaminopyridine, 4-aminopyridine, and acetazolamide.[8] Several therapeutic approaches, such as contact lenses,[9] drugs, surgery, and low vision rehabilitation have also been proposed. Clinical trials of a surgery to treat nystagmus (known as tenotomy) concluded in 2001. Tenotomy is being performed regularly at the University of Pittsburgh Children's Hospital and by a handful of surgeons 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. [edit] ResearchSeveral universities are researching nystagmus and are looking for volunteers to take part in research activities. [edit] See also[edit] References
[edit] External links
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