Horizontal Gaze Nystagmus (HGN) is an involuntary jerking of the eyes that may indicate the presence of alcohol or drugs during a DUI investigation. DUI Attorneys in Orange County know that this is usually the first field sobriety test that the officer asks you to take when performing a DUI investigation. The test is supposed to be given when both the officer and the driver are standing, yet many cops perform it when the driver is still sitting in the car. The cop conducting the DUI investigation is then supposed to hold an object (stimulus) 12 to 15 inches from the driver’s face, just above eye level, while the driver follows the stimulus with ONLY their eyes. (The head is supposed to remain perfectly still.) The DUI officer is then supposed to move the stimulus slowly across the plane of the driver’s eyes. It is supposed to take 3 to 4 seconds to complete one arc but it is common for DUI officers to move the stimulus too fast. At least two passes are supposed to be performed. If any aspect of the Horizontal Gaze Nystagmus test is performed incorrectly, your Orange County DUI Lawyer should point this out to the jury.
The theory is that as the eyes move from side to side, the movement
should be smooth, like two marbles rolling across a flat polished glass
surface. The presence of alcohol can cause the eyes to move less smoothly—like two
marbles rolling across course sand paper.
The officer conducting the DUI investigation is supposed to
start moving the stimulus from the center, moving to one side. The DUI
investigator is supposed to keep moving the stimulus to the side until the cop
cannot see any white of the eye. (maximum deviation) This usually occurs at
about 45 degrees. The DUI investigator is supposed to hold it there for four
seconds before moving the other way. When the stimulus is at maximum deviation,
a slight jerking of the eye, called nystagmus, will occur in about half the
population. However, if alcohol is on board, the nystagmus becomes very
distinct. This “distinct nystagmus” is a clue that the DUI investigator looks
for. The earlier the nystagmus occurs the more alcohol is in the persons
system. Therefore, the DUI investigator is also looking to see at what angle
the nystagmus occurs. If nystagmus occurs before maximum deviation, the DUI investigator
is supposed to hold the stimulus at that spot for at least two seconds while
noting the angle of onset.
Nystagmus occurring at an angle of about 40 degrees is
roughly correlated with a blood-alcohol of 0.10%. Nystagmus occurring at 35
degrees equates to a BAC of 0.15%, and at 30 degrees with a BAC of 0.20%. In
DUI trials, prosecutors often attempt to have the arresting officer estimate a
BAC based on the angle of onset. A good DUI Lawyer in Orange County will
object to the introduction of the officer’s opinion as to a specific BAC as
this evidence is not reliable enough to be admitted. The DA can only use this
test to show that alcohol is present in the driver’s system and anything
further MUST be objected to by your DUI lawyer.
If you have been arrested for DUI in Orange County and would
like to consult with an Orange
County DUI lawyer, call the Law
Offices of EJ Stopyro at (949) 559-5500
to today. The consultation is free and
confidential. Or visit our website at www.EJEsquire.com.
Law Offices of EJ Stopyro
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