re: My first encounter with an a-hole cop

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ne test that is not standardized but is often used and taught in the certification classes taken by police officers is the Vertical Gase Nystagmus (VGN) test. The VGN is similar to the Horizontal (HGN) test, except it tests for Nystagmus in the eyes when looking upwards instead of from left to right. A “positive” result on a VGN test could indicate that a person is severely intoxicated from alcohol, or it can be an indicator that a person is under the influence of other drugs such as CNS depressants, inhalants, or Dissociative Anesthetics like PCP.

What is Vertical Gaze Nystagmus?
Nystagmus is a medical term that refers to an involuntary jerking of the eye which can be an indication of intoxication from alcohol or certain types of drugs. Before beginning the test, the officer should check for resting nystagmus and the ability to track objects with the eyes, either of which could be an indicator of a medical condition that has nothing to do with intoxication.

VGN is not typically conducted as a stand-alone FST. Usually the officer will conduct the HGN test and then check for VGN as a part of the HGN test process. VGN is often described as a drug test or a marijuana test, but this is not accurate – VGN will only indicate intoxication by drugs that would also cause HGN. It is nevertheless useful because, regardless of BAC, VGN should only appear at higher levels of impairment.

The test subject should stand with their head perfectly still as the officer holds a small penlight, pen, or other small object 12-15 inches from the person’s eyes and then moves it upwards 12-15 inches in a fluid motion that should take about one second. The officer will then hold the position for four seconds while checking the eye for nystagmus. If the eye twitches while looking upwards the person has VGN. If the eye does not twitch, or if it twitches then stops before the four seconds are up, the person does not have VGN.

Is the VGN test reliable?
Like the HGN test, VGN is not a reliable indicator of intoxication when conducted alone. NHTSA has determined that HGN is a reliable indicator of impairment only when conducted in conjunction with the one-leg stand test and the walk and turn test, and only when the officer follows the protocol that NHTSA has laid out for administering each of the tests.

Nystagmus is a medical condition and, although they may be certified in administration of SFST’s, officers are typically not doctors or medical professionals. Nystagmus can be caused by intoxication. Nystagmus is also caused by many other medical conditions that are completely unrelated to intoxication, and most police officers have no idea what these conditions are or how to diagnose them. Nystagmus can be caused by:

multiple sclerosis
brain tumor
head injury
eye injury
hyperventilation
flashing a light in front of one eye
legal medications
nicotine
diabetic neuropathy
inner ear disorders
water in the ear
eye strain
neurological disorders
This is by no means a complete list – there are many more conditions that can cause nystagmus which is why the HGN or VGN test must be done in conjunction with other tests and there must be other indicators of intoxication in addition to HGN or VGN.

The South Carolina Supreme Court has held in State v. Sullivan that HGN (and VGN by implication) is sufficiently unreliable that it is not even admissible as evidence of DUI unless it is offered in conjunction with other tests. It is not conclusive evidence of DUI, it is circumstantial evidence only, and it cannot establish a specific degree of blood alcohol content:

This Court concludes that evidence resulting from HGN tests, as from other field sobriety tests, is admissible when the HGN test was used to elicit objective manifestations of soberness or insobriety. See State v. Nagel, 30 Ohio App.3d 80, 506 N.E.2d 285 (1985). We hold that evidence arising from HGN tests is not conclusive proof of DUI. A positive HGN test result is to be regarded as merely circumstantial evidence of DUI. Furthermore, HGN tests shall not constitute evidence to establish a specific degree of blood alcohol content. See State v. Garrett, 119 Idaho 878, 811 P.2d 488 (1991).

We hold that testimony relating to the HGN test was admissible in the present case because the HGN test was used in conjunction with other field sobriety tests to establish evidence of DUI.

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