Traffic Violations

Standard Field Sobriety Tests-Part I: HGN

The police almost always conduct field sobriety tests when they pull over a driver who they suspect was drinking and driving did you ever wonder why?

The standard field sobriety tests (SFST’s) are important to the police for two reasons:

  • First it establishes probable cause (well grounded suspicion) that a driver is intoxicated which allows them to arrest the driver and bring him or her back to the station to administer the Alcotest.
  • Second, in case the Alcotest gets thrown out for whatever reason, they can still prove intoxication beyond a reasonable doubt based on the subject failing their field sobriety tests.

The problem is that the field sobriety tests are completely subjective…


The first test is always the horizontal gaze nystagmus (HGN). Before an officer or trooper can testify to HGN testing, they must successfully complete the designated training and be certified by the state. This is achieved by the review of twenty completed tests where the breath or blood test showed that the HGN testing was in properly administered.

Nystagmus is the involuntary jerking of the eyes.

The police officer is trained in the New Jersey State Police DWI\Standardized Field Sobriety Testing Course to ideally utilize a penlight at roadside to assist in the administration and observation of potential nystagmus in the suspect’s eyes.  This is despite the fact that use of a flashlight is not recommended due to the probability of casting of shadows which will make it more difficult to make a fair assessment of the presence of a nystagmus. It may obviously create a problem for the suspect in following the stimulus as it will cause an artificial blinding.

The Horizontal Gaze Nystagmus Test is not a test of vision, but it is imperative that the suspect be able to follow the stimulus in order to make an accurate scoring of this test.  The suspect must be instructed to look straight ahead, keeping the head still while following and focusing on the stimulus with the eyes until told to stop.

The stimulus must be twelve to fifteen inches in front of the suspect’s eyes for ease of focus.

The officer is trained to receive an acknowledgement from the suspect that the stimulus is at a comfortable distance from the suspect’s eyes and to document it as such.  Even though this test is not a vision test, per se, eyeglasses are to be removed in order for the officer to make a more accurate determination of the final total points.

If the suspect cannot see the stimulus after removing the eyeglasses, they must be allowed to perform it with them on.  The manual says not to administer the test if the suspect is wearing hard contacts.  In addition, a person with a glass eye or only vision in one eye cannot be given this test, as an evaluation of just one eye and a doubling of the score (assuming that the other eye will render the same results) is both erroneous and improper.

The HGN test is clearly not designed for people with vision problems in mind.  As a result, the findings from this field sobriety test are incredibly untrustworthy and a perfect example of how they are also completely subjective.  If you’ve failed the SFSTs because of an eye condition, call me, attorney Leon Matchin, immediately at (833) 732-7320 to fight your DUI/DWI charge.

This leads us to our next part of the Standard Field Sobriety Tests, Part II: Optic Medical Conditions where we will look further into the medical conditions of a nystagmus and its effects on these assessments.

Come visit me next week to learn more!

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