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Pathological nystagmus
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.
(American Nystagmus Network) 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). 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.
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. 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. In milder cases, the patient is often asked to fixate on an
object, or wear fresnel lens glasses, which blur vision, to bring out the
nystagmus. Positional nystagmus is the opposite of spontaneous nystagmus in that
it occurs when the patient's head is in a specific position (e.g., benign
paroxysmal positional vertigo; BPPV). A video of the Nystagmus associated with
BPPVcan been seen here.
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