What is “Distinct and Sustained” Nystagmus?

Introduction:

The Standardized Field Sobriety Tests and Drug Recognition Expert examination have been used for decades to detect impaired drivers. They’ve been proven to be accurate in detecting impairment resulting from use of alcohol, cannabis, and other classes of drugs. However, DUI defense attorneys have found that they can upend a DUI case reliably by attacking these tests. Was the officer properly trained, did they perform the tests accurately, did they interpret the tests accurately, and were the background distractions managed appropriately for both the officer and the suspect? These questions are far from trivial, and many DUI charges have been dismissed based on the lack of data generated by the tests.

For alcohol and depressant drugs, the nystagmus tests are likely the most predictive of impairment and therefore the most important to get right.

What is Nystagmus?

Nystagmus is an involuntary eye movement in which the eyes make involuntary, repetitive, and rhythmic movements. These movements can be side-to-side, or up-and-down and are characterized by a fast movement component then a slower movement component. Nystagmus can affect one or both eyes, and it can be mild or severe.

The video below shows an example of alcohol induced nystagmus as recorded by Gaize:

What is “Distinct and Sustained” Nystagmus?

The threshold for nystagmus that an officer looks for is “distinct and sustained.” It is one of the three clues that law enforcement officers are trained to look for during the horizontal gaze nystagmus (HGN) test. There are several important conditions that all must be met for the nystagmus to be considered distinct and sustained.

• The jerking of the eye must be noticeable and easily observable.

• The jerking must continue for a minimum of four seconds.

• The jerking must occur when the eye is held at maximum deviation.

A few other important notes on this test are:

• The jerking of the eye will be more pronounced in the direction that the eye is being deviated.

• The jerking will be more noticeable in the upper eyelid than in the lower eyelid.

• The jerking will become more pronounced as the eye is held at maximum deviation.

How is the HGN test performed?

To manually perform the the HGN test, the officer will ask the driver to follow a small object, such as a pen, with their eyes as it is moved slowly from side to side. The officer will look for three clues of nystagmus in each eye:

Lack of smooth pursuit: The eyes should smoothly track the object as it is moved. If the eyes jerk or wobble as they track the object, this is a clue of nystagmus.

Distinct and sustained nystagmus at maximum deviation: The eyes should continue to jerk or wobble even when they are held at maximum deviation. If the jerking or wobbling stops after a few seconds, this is not a clue of nystagmus.

Onset of nystagmus prior to 45 degrees: The jerking or wobbling should begin before the object is moved 45 degrees to the side. If the jerking or wobbling does not begin until the object is moved more than 45 degrees to the side, this is not a clue of nystagmus.

The presence of three or more clues of nystagmus is considered to be a reliable indicator of alcohol or depressant drug intoxication. However, it is important to note that nystagmus can also be caused by other factors, such as neurological disorders and certain medications. Therefore, the HGN test should not be used as the sole basis for a DUI arrest. Other factors, such as the driver's performance on other standardized field sobriety tests and the results of a breathalyzer test, should also be considered.

Police departments have also started adopting Gaize to automatically conduct the DRE eye tests and record video evidence. This technology is a radical advancement for DUI cases.

The rise of video evidence in impairment cases:

Gaize produced high quality video evidence of eye movement during perfectly performed Drug Recognition Expert eye tests. The above video is unaltered output of the Gaize headset. This is of significant value for law enforcement officers, judges, juries, and attorneys on both sides of the case. It’s vital that the truth be available to see.

Learn more about Gaize for law enforcement use by visiting this page.