[ARCHIVE ANSWER]

The "pen test" to law enforcement is called "horizontal gaze nystagmus." Nystagmus is defined as the involuntary jerking of the eyeballs. Under a microscope every person's eyeball flutters back and forth. Alcohol intoxication makes this fluttering or jerking visible to the naked eye. During a test, officers look for three things:

1) EYEBALLS LACKING SMOOTH PURSUIT- The officer has the suspect track a moving pen. Alcohol intoxication causes the eye to lack a smooth pursuit of a moving object.

2) NYSTAGMUS AT MAXIMUM DEVIATION – The officer views the eyeball when the suspect stares at a stationary pen positioned at maximum deviation meaning the furthest to the right or left. (The head is kept still, and the eyes are cocked as far as they
will go.) Next time you are drunk, cock your eyes to maximum deviation, and you will see the room or landscape moving. This is the involuntary jerking of your eyeballs causing this.

3) NYSTAGMUS AT OR BEFORE 45 DEGREES – Same as maximum deviation, only the officer views the eyeball when the suspect stares at a stationary pen located between the nose and ear.
The horizontal gaze nystagmus test is not junk science and does work. Out of the three, officers rely mostly on number two described above, but are suppose to administer and take into account all three. A person has to be really intoxicated to see nystagmus at or before 45 degrees. A large number of officers perform this test and are not certified to do so. If this is the case, the test can easily be thrown out of court.

Citizens can check each other for nystagmus to advise whether their friends can drive safely or not. This test can also be performed to see if marijuana causes nystagmus.

Can a person influence the outcome? Yes. Refuse to take the test or do not cock your eyes all the way for the maximum deviation test. NeverGetBusted believes if a person is truly intoxicated to the point of losing use of their normal mental and physical faculties, they belong in jail.