The HGN (Horizontal Gaze Nystagmus) test is often known as the “pen” or “light” test.  This is because the officer administering the test usually uses a pen or flashlight to perform the test.

Without moving your head, the officer will ask you to follow a “stimulus” (usually a pen, a flashlight, or his or her finger) with your eyes as it arcs further and further towards your periphery.  In administering the HGN test, the officer is looking for up to six (6) clues of a twitching or jerking of your eyeballs prior to 45 degrees.

REMEMBER: Nystagmus is generally defined as the involuntary movement of the eyeballs, and can be , but does not by definition have to be, a result of a high blood-alcohol content.

Though that is certainly the  conclusion that an officer administering the test would like to draw, there are many alternative and justifiable explanations for nystagmus that do not require any blood alcohol concentration at all.

For instance, one may suffer from Nystagmus due to a neurological disorder, inner ear problems, congenital disorders, or occupational or labrynthine irritability.  If you suffer from any medical conditions including but not limited to these (there are about 100 non-alcohol related conditions that might cause nystagmus) and the officer administering the HGN test does not inquire about them, and/or the test was not administered properly, the scientific weight and admissibility of these results may be attacked.