One of the most common
Standardized Field Sobriety Tests used by police to determine if probable cause exists for a drunk driving
arrest is the Horizontal Gaze Nystagmus (HGN) test. This test works by
measuring a driver’s eye reflexes when asked to look at a moving
stationary object at a close distance, allowing officers to look for certain
key signs of intoxication.
How Does the Test Work?
Nystagmus is the medical term used to describe an involuntary twitch of
the eyeballs which occurs when a person looks sideways at an angle greater
than 45 degrees. When a person is under the influence of alcohol or certain
drugs, this jerking become more pronounced and can occur at angles less
than 45 degrees.
To administer the test, an officer must first check a driver’s eyes
for any resting nystagmus, equal pupil size, and the ability to equally
track and object with both eyes. If a driver cannot do any of these things,
there is a possibility that they have an existing medical condition which
may render the test result unreliable. To properly administer the test,
an officer must hold a small object rough 12-15 inches away from a driver’s
nose, usually a flashlight or pen, and slowly move it from side to side
while the driver follows it with their eyes.
Officers will look for several signs of intoxication, including:
- A lack of smooth pursuit
- Eye jerking before reaching a 45 degree angle
- Eyes jerking within four seconds while gazing all the way to one side
Are HGN Tests Accurate?
The National Highway Traffic Safety Administration (NHTSA) has determined
that HGN tests are reliable as long as they are administered by a police
officer who has had proper HGN training. If a subject’s eyes are
not properly visible, if they are facing blinking lights or oncoming headlights,
or if the subject has their eyeglasses on at the time of the test, the
results could be skewed. It is also important to note that HGN tests are
not pass/fail, but merely a way for police to gain a possible indicator
of a driver’s intoxication. For this reason, many states do not
allow the test to be used as evidence in a court of law.
Charged with DUI? Call JD Law
If you have been arrested and charged with
driving under the influence (DUI), it is imperative you contact a powerful criminal defense attorney as
soon as possible to guard your future and freedom. Having been guarding
the rights of the accuses for more than 30 years, our powerful San Diego
DUI attorney can contest the evidence against you and provide the top-notch
advocacy you need to minimize your chances of conviction.
Find out more about what our Board Certified Criminal Law Specialist can
do for you by calling our office at (619) 377-3722 or by
scheduling a free consultation.