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.
People with nystagmus may not be aware of their eye movements because what they see usually does not appear shaky to them. People with nystagmus may tilt or turn their head in order to see more clearly. This helps to dampen or slow down the eye movements.
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.
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