HGN Test in a DUI Stop

HGN Test in DUI Arrest

The Horizontal Gaze Nystagmus is a commonly used field sobriety test.  It is

An incorrectly administered HGN Test

also known as the pen test.  Nystagmus is the involuntary jerking of a person’s eye when they gaze to one side.  Impaired subjects exhibit more pronounced jerking or bouncing.  Alcohol is a central nervous system (CNS) depressant and inhibits the brain from effectively controlling eye muscles.  Other common forms of CNS include Valium, Xanax and Ambien.  Under A.R.S. § 28-1381 Subsection B, if a person has a valid prescription and are taking the drug as prescribed they may not be guilty of driving or operating under the influence.  Accordingly, the HGN is suspect because the test does not differentiate between prescription drug-related nystagmus and nystagmus related to alcohol consumption.  Police Officers administer this test and two other tests all of which are standardized field sobriety tests.  The HGN is a subjective test and to be administered correctly a number of factors have to be correct at the time of the examination. Those factors include the officer’s skill in administering the test and properly assessing impairment.  The HGN test is a very complex and scientific procedure, it is possible that an unskilled officer could misinterpret eye jerking or bouncing.  Nystagmus is also caused by nearly one hundred medical conditions, and even the most skilled officers are not doctors.