The Science Behind HGN in Driving Under the Influence Cases

Michael S. Herring, Esquire's DUI/DWI Legal Blogs

Licensed for 32 years

Attorney in Sanford, FL

Michael S. Herring, Esquire

Free initial consultation, Credit cards accepted, Fixed hourly rates

Serving Sanford, FL

  • Serving Sanford, FL

  • Free initial consultation, Credit cards accepted, Fixed hourly rates

Senior Attorney at firm Herring and Herring, P.A.

Serving Sanford, FL

Free initial consultation, Credit cards accepted, Fixed hourly rates

Awards AV Preeminent

you have been stopped by police in Seminole County, Florida and ultimately
accused or charged with DUI, beware of the “HGN Exercise” or “pen test”.

Court’s in Sanford, Florida have wrestled with admitting this test into
evidence. In Seminole County, Florida, as of the date of this posting, most
Judges will not allow the officer to testify about the results of the test as
he/she observed, but will allow the State of Florida to show the jury the video
(sometimes with audio muted) of the performance of the HGN test. The
administering police officer is not allowed to testify as to the scientific
evidence he/she supposedly gleaned from the test. The test involves the officer
telling the person to hold their head rigid and using only their eyes to follow
a pen or a stylist held about 12-15 inches in front of them. When instructed to
begin, they are told to follow the object with both eyes as the pen or stylist
is moved horizontally from center point to the outside reach of the eyes. The
test is supposed to show the onset of nystagmus, or an involuntary jerking of
the eyes, before the eyes reach 45 degrees from center. The reasons for the
limits on admissibility are many, including: the officer’s inability to
decipher the test result; a person can exhibit premature HGN with no alcohol in
their system; and the failure of the testing officer to obtain specific
background information about the subject’s medical history to explain early
nystagmus was caused by the condition. Preexisting conditions of the eye,
including diseases of the eye, etc. can affect the results of the test and thus
admitting such a test under the guise of its scientific accuracy without
complying with certain pre-test protocols may impermissibly mislead the jury.
Thus, the arresting officer’s failure to obtain background medical information
on the test subject can cast doubt that the early onset of HGN is caused by
excessive alcohol consumption alone. The Court in Sanford, Florida have
however, generally allowed testimony from the arresting officer relating to the
subject’s inability to follow instructions on how to perform the task and let
in video evidence of this pre-arrest roadside task so the jury can observe any
lack of coordination or unsteadiness of the subject while performing the test.
While HGN introduction has been limited in Seminole County, Florida, DUI
prosecutions, the HGN is reputedly the best pre-arrest indicator of impairment
if pre-test protocols are rigidly followed

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