Saccades

Saccades are quick, simultaneous movements of both eyes in the same direction. Initiated voluntarily or automatically, they are the fastest movements produced by the human body. The peak angular speed of the eye during a saccade reaches up to 900 degrees a second. Saccades are one of several types of eye movements, others being smooth pursuit and vestibulo-ocular movements.

Function

Saccades serve the function of redirecting the fovea to a target in the peripheral vision. The fovea is a small, central pit composed of closely packed cones in the eye. It is responsible for sharp, central vision, which is necessary in humans for activities where visual detail is of primary importance, such as reading and driving.

Characteristics

Saccades are one of the fastest movements produced by the human body. The peak angular speed of the eye during a saccade reaches up to 900 degrees a second. The duration of a saccade depends on its amplitude. For amplitudes up to 15 or 20 degrees, the duration is roughly proportional to the amplitude (a rule known as saccadic main sequence), but for larger amplitudes, the peak speed is limited to around 900 degrees/s.

Types

There are two types of saccadic eye movements: voluntary saccades and reflexive saccades. Voluntary saccades are those made intentionally. These are often made in response to instructions given by an experimenter. Reflexive saccades are those made automatically. These are often made in response to a sudden peripheral or unexpected stimulus.

Disorders

Saccadic disorders can manifest in a variety of diseases including Parkinson's disease, Huntington's disease, Alzheimer's disease, schizophrenia, and multiple sclerosis. They can also occur as a result of drug use, alcohol intoxication, or sleep deprivation.

See also

• Eye movement
• Smooth pursuit
• Vestibulo-ocular movements
• Parkinson's disease
• Huntington's disease
• Alzheimer's disease
• Schizophrenia
• Multiple sclerosis

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