What is ‘Nystagmus’?

There is a naturally occurring phenomenon of the eyes known as ‘nystagmus.’ Nystagmus – an involuntary twitching or jerking of the eye that varies from fast to slow – typically occurs when a person stretches the eyes’ ability to look in a particular direction at an angle of about 45 degrees while the head is held still in the forward position. A person is unaware of experiencing nystagmus.

There are 47 kinds of nystagmus and they occur under different circumstances. For instance, a person experiencing vertigo would have symptoms of nystagmus. Spinning around quickly and repeatedly creates post-rotational nystagmus as the fluids in the vestibular system become unbalanced.

Horizontal gaze nystagmus is used as an indicator of intoxication as the eye movements of a sober person differ greatly from those of an impaired person. This test is one of the standardized field sobriety tests created by the NHTSA. Vertical gaze nystagmus is used to determine if a person is under the influence of a variety of drugs, although it is not a standardized field sobriety test.

It is important to note that nystagmus is a naturally occurring phenomenon of the eyes; drugs and/or alcohol only increase or exaggerate the twitching or jerking of the eyes.