Failing the 'Float Test': Boating While Intoxicated

I usually don’t pile on when a celebrity as arrested and the best way to do that is to not blog about the arrest. And while it’s worth noting that I have no personal knowledge of the facts in this case, nor do I represent the accused, this post is at least nominally in defense of Cedric Benson. (And to further my bona fides on sticking up for Benson, see this post.)

This part of the AP story about Cedric Benson’s arrest for Boating While Intoxicated in Austin jumped out at me:

According to a sergeant from the Travis County Sheriff's office, Benson, who played at the University of Texas in Austin, was arrested by the Lower Colorado River Authority. A LCRA spokesperson said that Benson, who failed a sobriety "float test" (an abbreviated version of a field sobriety test) on the boat, argued over taking a follow-up test on land and refused to put on a life jacket.

So they’re calling it a “float test” now. Never heard that one, but lemme take an educated guess at what they’re talking about.

Prior to taking someone to shore, a law enforcement officer asks the subject – in this case Chicago Bears running back Cedric Benson – to do some tests to prove his sobriety while he is still standing on his boat. While it’s on the water. Moving around. Waves underneath the boat.

Once the subject is unable to prove to the officer’s satisfaction that he isn’t intoxicated, he is asked to come ashore and then the standardized field sobriety tests are administered.

Putting aside for the moment that the FSTs are junk science at best to start off with, the officer then testifies in court – because it’s consistent with his training – that a 15 minute waiting period after coming off the boat is sufficient for the subject to regain his land legs, and to do the tests in a manner that puts him on equal footing with someone that hasn’t been out on a lake all day.

This 15 minute time period, as far as I’ve ever been able to tell, is completely made up. There are absolutely no scientific studies to show this. I’ve always suspected that whoever came up with it basically ripped off the idea from the 15 minute observation period required by Texas DPS in a breath test case.

One last note: I’m not saying that Cedric Benson is not guilty – I don’t know. Perhaps he was tanked. More likely than not, there was at least evidence that he had consumed some alcohol. But there’s a really big difference between those two, and conducting what the news media, if not the police, are now calling a float test to determine where on that bell curve he was? If it was anything like the boating while intoxicated cases I’ve seen in my career, I wouldn’t put much stock in it.

Do Police Have to Tell Suspects That the DWI SFSTs are Voluntary?

This question via the internet. (Feel free to email me other questions about Texas DWI laws.)

Well, let me change the way the question is phrased. It’s a standard question I hear, but from those who have already been arrested and charged with DWI. Invariably, it comes from someone who took the standardized fields sobriety tests (SFSTs), and more likely than not, is let’s say ‘nervous’ that they didn’t do so well on them.

In that instance, what the client is really asking his DWI lawyer is, “The police officer didn’t tell me I could refuse to do the tests. Can you get them thrown out / ignored / suppressed?”

No, at least not on that basis. Police are not required in Texas, or anywhere else that I’m aware of, to tell DWI suspects that they may politely refuse. In fact, it’s quite the opposite.

I’ve seen quite a few DWI videotapes from Austin arrests where the officer tries to convince the person out on the scene that they should take the tests, even after they politely refuse. Some of the time the officer pretends to not understand that my client is even exercising their right not to submit to the tests.

Other times, they’ll say “OK, but you don’t know what I’m going to ask you to do… Let me just demonstrate the test for you…”

The ‘demonstration’ of course, includes standing with your feet together, hands at your side, place your right foot in front of your left foot, stay in that position until I tell you to start… in other words: the test has begun before the officer fully demonstrates it.

However, there’s a more important aspect of this question from my perspective. It’s what I call ‘spilt milk’.

If you’ve recently been arrested for DWI, more likely than not, you’re playing the ‘split milk’ game. 

  • If only I had turned right instead of going straight. 
  • If only I had left the bar earlier (later?)
  • If only I had taken a cab. Etc., etc.

There’s no point crying over spilt milk. We’ve got to play the cards we’re dealt, and that’s OK. I tell my clients to give themselves 2 or max 3 more days to beat themselves up over the arrest, and then let’s get on with building our defense.

In Austin, the DWI process takes several months, four to six months usually, sometimes longer. You’ll drive yourself crazy if you play “I should have done this differently” the whole time.

The Overconfident Police Witness in DWI Cases

Stephen Gustitis recently commented on a study done at Berkeley that ‘debunk[ed] conventional wisdom on trial witnesses’:

The researchers concluded that self-assured witnesses who make a mistake - even on issues of little importance - undermine their credibility by raising doubts about their competency, their ability to judge their own abilities and their motivations.

"People giving testimony, or advice, or opinions should therefore be careful to express appropriate degrees of confidence in their assertions," the researchers write in a summary of their report in the January issue of the journal Psychological Science. "Otherwise, the 13th stroke of the clock will cast the other 12 in doubt."

I take issue with the title of that article, because I doubt that is the conventional wisdom, at least of those who should know. As Stephen says, the study ‘confrimed what experienced criminal defense lawyers already knew’:

The cocky, arrogant, or over-confident witness builds a wall between themselves and the jury. Since normal, ordinary, and reasonable people know we all make mistakes, the over-confident witness projects an air of superiority which juries tend to resent. Consequently, when the witness is caught in a mistake the jury is quite happy to punish him by greatly devaluing his credibility.

The over-confident witness is often one testifying as an expert, but the problem also affects the lay witness. The experienced defense lawyer preparing these witnesses for court will recognize the problem and take appropriate steps to temper their over-confidence.

100% correct. And this leads me to one of my favorite things about DWI cases. Since DWI is an opinion crime, the arresting officer will find himself caught up in this phenomenon in almost every case.

When it comes to evaluating a defendant’s performance on the field sobriety tests, yes, NHTSA has their ‘standards’, but even the manual doesn’t attempt to suggest that everyone will do perfectly. Or even that all defendants who exhibit X number of clues on the [HGN, Walk and Turn, One Leg Stand, etc.] are intoxicated.

Consequently, when asked in cross examination whether my particular client could have exhibited the clues on videotape, but not be intoxicated, the officer has two choices:

(1)   He can admit it’s possible that things other than intoxication could have caused my client’s ‘errors’ on the test.

(2)   He can express with 100% confidence and certitude that the only reason for my client’s foot coming off the imaginary line is absolute proof of intoxication.

Frankly, I’m fine with either answer. In a lot of cases, I prefer answer #2. Jurors know #2 is wrong wrong wrong; and as the study suggests, it will reduce the juror’s natural tendency to ‘believe what the officer says’.

In fact, seasoned officers know this as well. In my experience, almost all of the Austin DWI Task Force officers will testify either at pretrial or at the ALR hearing that the tests are not 100% accurate, and that factors other than alcohol or intoxication can cause some missteps on the FSTs.

Of course, that’s not really such a bad answer either.

[Also see: Certainty of the Witness.]

DWI Cross Examination of the Arresting Officer

Kevin Smith of Wichita, Kansas writes about his ‘Matlock Moment’ in a recent DWI jury trial.

His client’s situation was familiar to DWI lawyers everywhere. The defendant looked fine when walking, talking, and interacting with the officer except… when it came to doing those Field Sobriety Tests.

To win a DWI case, the defense lawyer must often come up with a plausible explanation of why the client does poorly on the agility tests, other than intoxication or impairment. In Kevin’s case, his female client was wearing 2 inch high heel shoes.

Kevin’s description of the key moment in trial:

The "not guilty" verdict came down to a question.

Before I reveal the question it will help to picture the officer first. He's about 6'4", roughly 250 lbs. (with a sizable belly to boot), bald, and very tough looking.

So here's the question: "You probably would have done as bad on the field tests had you also been wearing two-inch high heels, wouldn't you?"

He responded, "Maybe, but I can't tell you for sure since I've never worn high heels."

Excellent example of distilling the defense case down for the jurors to ‘get it’. 

And, it’s an example of that rare type of cross examination question: you don’t know the answer, but you don’t care how the officer responds. He can either - as in this case - answer truthfully, which helps your client; or he can hem and haw and sound unreasonable. I’d almost prefer to hear the officer’s explanation of why high heels wouldn’t affect his performance on the FSTs. The jury will still get the point.

Kevin doesn’t say whether he had the officer read this portion of the NHTSA DWI Manual to the jury:

The original research indicated that individuals over 65 years of age, back, leg or inner ear problems had difficulty performing this test. Individuals wearing heels more than 2 inches high should be given the opportunity to remove their shoes. [DWI Detection and Standardized Field Sobriety Testing, 2006 NHTSA Manual, VIII-11. Emphasis Mine]

Doesn’t sound like this officer offered Kevin’s client the opportunity to take off her shoes, and that can be an important point to put in front of the jury.

Of course, when you get an answer as good for the defense as Kevin got, it may not be necessary.

Larry Craig and DWI Cases

Public Defender Dude on “Larry Craig and Police Officer Opinion Testimony”:

One of the areas that has held public fascination in the Larry Craig situation is the vagueness of the charges and allegations against him. Put simply - what did he actually do wrong - tapping a foot and reaching with his hand? He clearly did not break any established and obvious laws by those actions… So what he did had to be interpreted by a police officer as being illegal, because it is not illegal on its face.

This brings up an area that I've so often railed against - police officer opinion testimony (or, as I like to put it, "my opinion is that you're guilty."). I think that this opinion testimony, whether in the context of gangs (giving an opinion that any sundry crime was committed for the benefit of a street gang so as to make minor crimes strikes, or average crimes life sentences), or drugs (giving the opinion that whatever amount of drugs that someone possessed was obviously possessed for purposes of sale), or any other area.

Prosecutors love this stuff. It's like 2 closing arguments in their case. They get a police officer who gets to get up on the stand and essentially say "I've investigated thousands of cases, and in my opinion this person is guilty, because his case falls in with all these other ones in this manner."

It is highly prejudicial, and in many cases, highly meaningless.

It struck me when I read his post that PD Dude is also accurately describing so many officers’ testimony in DWI cases, as it relates to the defendant’s performance on the Field Sobriety Tests.

“In my opinion, he should have done better on these agility tests, and because he didn’t, in my opinion he’s guilty of DWI.”

DWI lawyers must point out that the officer’s opinion doesn’t factor in

  • Initial nervousness for being pulled over for a traffic violation
  • Increased nervousness now that you know you’re being investigated for DWI
  • You might be non-athletic, or perhaps even a klutz
  • Or that Field Sobriety Tests don’t measure a person’s normal abilities to do anything

As PD Dude says, you may just be able to show that the police officer’s opinion is “highly meaningless”.

Signs or Clues of Intoxication in DWI Cases

Police Officers are trained to look for certain ‘common’ signs of intoxication when evaluating a suspect for DWI. Some of these are thought to be so frequently exhibited in DWI cases, that the local police agencies in Austin have pre-printed forms for probable cause affidavits so that they can quickly check off boxes - and, then, presumably, move on to the next arrest.

The Austin Police DWI affidavit form includes checkboxes for:

  • Odor of Alcohol: Strong, Moderate, Faint, None
  • Eyes: Bloodshot, Watery, Glassy, Dilated, Constricted
  • Speech: Mumbled, Slurred, Confused, Not Understandable, Mushmouthed, Stuttered, Fair, Good, Accent, Thick Tongued
  • Balance: Wobbling, Falling, Swaying, Unsure, Needed Support
  • Attitude: Excited, Hilarious, Talkative, Uncooperative, Profanity, Polite, Sleepy, Combative, Indifferent, Cooperative, Insulting, Cocky
  • Walking/Turning: Falling, Swaying, Staggering, Stumbling

Other than “No Odor of Alcohol,” “Fair/Good” speech, and “Polite/Cooperative” attitude, all the others are arguably signs of intoxication. And the more that are checked off, the more the State believes they have a strong case. 

But aren’t there perfectly good reasons why someone could exhibit several or many of these that aren’t reliable indicators of intoxication? Of course.

Some of the reasons other than intoxication include medical conditions, personality traits and physical characteristics/abilities of each individual. I will explore each of these in upcoming posts.

NHTSA Field Sobriety Test "Accuracy" Rates; What Do They Really Mean?

Dr. Greg Kane at Med-Mal Experts has published an excellent 3 part series on the flawed math that NHTSA uses to calculate “accuracy rates” for the Field Sobriety Tests. These papers were originally published in the Colorado Trial Lawyer’s Association magazine Trial Talk, and are now reproduced on Kane’s website “The predictive value of the NHTSA’s Standardized Field Sobriety Tests”.

Ultimately, Kane answers the question that all DWI lawyers need to be asking: What does it really mean when the officer testifies that “failure” of the field sobriety tests means there is a 93% chance that the defendant was intoxicated? How did NHTSA come up with that number…and is it meaningful?

From Kane’s site:

Around the country, DUI defense attorneys form organizations, give seminars and share trial strategies to overcome FST evidence. Prosecutors do the same, from the other direction. The two sides bicker about mechanics. Did the officer follow procedure exactly? Did the officer consider medical conditions that cause incoordination?

What no one does, as far as I can tell, is doubt the NHTSA "validation" contractors' analysis of what a mechanically meticulous coordination test actually implies about alcohol impairment. The driver failed the FST. No one asks, "Exactly what does that mean?"

I have to admit that he’s right. DWI defense lawyers and prosecutors tend to argue back in forth about whether the officer administered the tests properly. And any good DWI lawyer better know the NHTSA manual back and forth, so that when he watches the videotape of his client on the scene, he can evaluate the officer’s performance as well as his client’s.

But is it possible that we in the DWI defense bar have been missing the forest for the trees? I’ve digested the first paper thoroughly, and frankly, am truly excited about Kane’s work in these areas. As soon as I make it through the next two, I’ll post more on this subject.

Do Field Sobriety Tests Measure Impairment?

Every good DWI lawyer is familiar with the last section in Chapter 8 of the NHTSA DWI Detection and Standardized Field Sobriety Testing Manual that states:

If any one of the standardized Field Sobriety Test elements is changed, the validity is comprised. (***)

Indeed, one of the bedrocks of DWI defense is being able to grade not only the defendant’s performance on the FSTs, but being able to grade the officer’s administration of the tests. In some situations, improper instructions or grading can actually make an individual test or even the entire battery of tests inadmissible.

Unfortunately, for all NHTSA’s efforts to the contrary, there are many problems with these roadside tests – even when administered by the book.   They do not, in fact, allow police officers to accurately determine whether someone is over a .08 blood or breath alcohol content.

Furthermore, most of the better trained officers will admit under cross examination that there is no correlation between some of the tests and “impairment” – I know most of the specialized Austin DWI task force officers will testify to that, because I’ve asked them under oath. 

To the extent that “science” is involved here at all, the only real measurement is between performance on the tests, and being above or below a certain BAC.  Which means there’s an inherent argument for defense lawyers in many DWI breath test refusal cases that the client’s performance on the field sobriety tests is not sufficient proof of intoxication.

(*** Every NHTSA Manual I’ve ever seen actually has this section in ALL CAPS AND BOLD – emphasizing that even NHTSA acknowledges how important this is.)

NHTSA DWI Detection Manual - Glossary of Terms and Definitions

Alveolar Breath – Breath from the deepest part of the lung.

Blood Alcohol Concentration (BAC) – the percentage of alcohol in a person’s blood.

Breath Alcohol Concentration (BrAC) – The percentage of alcohol in a person’s breath, taken from deep in the lungs.

Clue – Something that leads to the solution of a problem.

Cue – A reminder or prompting as a signal to do something. A suggestion or hint.

Divided Attention Test – A test which requires the subject to concentrate on both mental and physical tasks at the same time.

DWI/DUI – The acronym “DWI” means driving while impaired and is synonymous with the acronym “DUI”, driving under the influence or other acronyms used to denote impaired driving. These terms refer to any and all offenses involving the operation of vehicles by persons under the influence of alcohol and/or other drugs.

DWI Detection Process – The entire process of identifying and gathering evidence to determine whether or not a suspect should be arrested for a DWI violation. The DWI detection process has three phases:

    • Phase One – Vehicle in Motion
    • Phase Two – Personal Contact
    • Phase Three – Pre-arrest Screening

Evidence – Any means by which some alleged fact that has been submitted to investigation may either be established or disproved. Evidence of a DWI violation may be of various types:

    • a.  Physical (or real) evidence: something tangible, visible, or audible.
    • b.  Well established facts (judicial notice).
    • c.  Demonstrative evidence: demonstrations performed in the courtroom.
    • d.  Written testimony or documentation.
    • e.  Testimony.

Field Sobriety Test – Any one of several roadside tests that can be used to determine whether a suspect is impaired.

Horizontal Gaze Nystagmus (HGN) – An involuntary jerking of the eyes as they gaze toward the side.

Illegal Per Se – Unlawful in and of itself. Used to describe a law which makes it illegal to drive while having a statutorily prohibited Blood Alcohol Concentration.

Nystagmus – An involuntary jerking of the eyes.

One Leg Stand (OLS) – A divided attention field sobriety test.

Personal Contact – The second phase in the DWI detection process. In this phase the officer observes and interviews the driver face to face; determines whether to ask the driver to step from the vehicle; and observes the driver’s exit and walk from the vehicle.

Pre-arrest Screening – The third phase in the DWI detection process. In this phase the officer administers field sobriety tests to determine whether there is probable cause to arrest the driver for DWI, and administers or arranges for a preliminary breath test.

Preliminary Breath Test (PBT) – A pre-arrest breath test administered during investigation of a possible DWI violator to obtain an indication of the person’s blood alcohol concentration.

Psychophysical – “Mind/Body”. Used to describe field sobriety tests that measure a person’s ability to perform both mental and physical tasks.

Standardized Field Sobriety Test Battery – A battery of tests, Horizontal Gaze Nystagmus, Walk and Turn, and One-Leg Stand, administered and evaluated in a standardized manner to obtain validated indicators of impairment on NHTSA research.

Tidal Breath – Breath from the upper part of the lungs and mouth.

Vehicle in Motion – The first phase in the DWI detection process. In this phase the officer observes the vehicle in operation, determines whether to stop the vehicle, and observes the stopping sequence.

Vertical Gaze Nystagmus – An involuntary jerking of the eyes (up and down) which occurs when the eyes gaze upward at maximum elevation.

Walk and Turn (WAT) – A divided attention field sobriety test.

Cross Examination: Watch the Witness

One of the purposes of allowing cross examination of witnesses is the idea of confronting your accuser. The theory is that the credibility and sincerity of a witness accusing you is best tested by live cross examination.

A few days ago, while sitting in court waiting for my client’s driver’s license suspension hearing to start, I watched an attorney conduct his cross of the officer who administered field sobriety tests to his client. The lawyer had a list of well prepared questions written out, which he then asked of the officer, one by one. Unfortunately, the method he used was basically to have his head down the entire time, reading the questions off of his legal pad.

When the lawyer got to the part about how the officer administered the HGN test, he had a pretty good line of questions he asked, such as:

            How long did you hold the stimulus at maximum deviation?

            How did you measure nystagmus prior to 45 degrees?

            How many total passes did you make during the HGN?

What the lawyer missed, by burying his head in his notes, was that the officer actually pulled a small “cheat sheet” out of his pocket, which gave him all the “correct” answers to these questions. These apparently weren’t notes from this particular arrest (trust me, no officer would make those sorts of detailed notes on every arrest), but just genereal guideline answers.

Not surprisingly, the officer got all of the questions right. But he was just reading his own pre-prepared notes, probably jotted down right of the NHTSA field sobriety test manual itself.

If the attorney had noticed this, he could easily have asked the officer to testify from his own memory of the event, or at least noted for the record that the officer was reading his answers from a sheet. Because he wasn’t paying attention to the witness, he missed this entirely.

One of the reasons I ask for driver’s license hearings in every DWI case is that it gives me the opportunity to cross examine the stopping and arresting officers. Several times, in cases that otherwise seemed somewhat hopeless, I have found out things about a DWI case that are extremely helpful. One of these things can be as simple as… the officer makes a really poor witness.

Complete and thorough preparation for cross examination is essential, but don’t forget to watch the witness testify. Evaluate his demeanor, and always ask yourself this: “Would this police officer make a good witness in front of a jury?”

What is Nystagmus?

Nystagmus is an actual medical phenomenon that describes an involuntary eye movement, or ‘ a jerking of the eyes’, as police officers often call it. Nystagmus can be difficult to detect, and has multiple causes, other than alcohol consumption.

Unfortunately, diagnosing both the complex medical condition itself, as well as divining its cause, has been boiled down to a few hours of a two and a half day Field Sobriety Test certification class, and taught to police officers across Texas and the United States as the ‘gold standard’ for DWI detection.

I can’t count the number of times I have heard the phrase “the eyes don’t lie” (from prosecutors, police witnesses, and others in law enforcement). Well, the truth is that when it comes to DWI detection, they do.

This blog will attempt to dissect truth from fiction, and to study what nystagmus is, what it isn't, what causes it, and why police officers so often believe that what they saw on the scene of an arrest during a DWI investigation really isn’t science at all. Stay tuned…

Field Sobriety Tests

More than half of police officers in Texas are certified to administer field sobriety tests to subjects stopped and being investigated for DWI.  The percentage is even higher in Austin.

The Austin Police Department created a specialized DWI Enforcement Unit (defense lawyers around here tend to refer to it as the ‘DWI Task Force’) in August of 1998. Since that time, arrests for DWI in and around Austin have more than doubled.

This blog will focus on DWI issues from the criminal defense lawyer’s perspective, and a great number of posts will be devoted to talking about the field sobriety tests, errors made in administration of the tests, and how to defend yourself against DWI charges brought primarily because of an officer’s opinion that you did not perform well enough on these tests.

Types of Nystagmus: 2006 NHTSA Manual

In Chapter 8 of NHTSA’s “DWI Detection and Standardized Field Sobriety Testing” Manual is a subsection entitled “Overview of Nystagmus”:

Nystagmus is defined as an involuntary jerking of the eyes. Alcohol and certain other drugs cause Horizontal Gaze Nystagmus.

Categories of Nystagmus

There are three general categories of nystagmus:

1. Vestibular Nystagmus is caused by movement or action to the vestibular system.

2. Nystagmus can also result directly from neural activity.

3. Nystagmus may also be caused by certain pathological disorders

Vestibular Nystagmus: NHTSA Manual 2006

Vestibular Nystagmus is caused by movement or action to the vestibular system.

A. Types of vestibular nystagmus:

Rotational Nystagmus occurs when the person is spun around or rotated rapidly, causing the inner fluid in the ear to be disturbed. If it were possible to observe the eyes of a rotating person, they would be seen to jerk noticeably.

Post Rotational Nystagmus is closely related to rotational nystagmus: when the person stops spinning, the fluid in the inner ear remains disturbed for a period of time, and the eyes continue to jerk.

Caloric Nystagmus occurs when fluid motion in the canals of the vestibular system is stimulated by temperature as by putting warm water in one ear and cold in the other.

Positional Alcohol Nystagmus (PAN) occurs when a foreign fluid, such as alcohol, that alters the specific gravity of the blood is in unequal concentrations in the blood and the vestibular system.

Nystagmus Resulting from Neural Activity: NHTSA Manual 2006

Nystagmus can result directly from neural activity:

Optokinetic Nystagmus occurs when the eyes fixate on an object that suddenly moves out of sight, or when the eyes watch sharply contrasting moving images. 

Examples of optokinetic nystagmus include watching strobe lights, or rapidly moving traffic in close proximity. The Horizontal Gaze Nystagmus test will not be influenced by optokinetic nystagmus when administered properly.

Physiological Nystagmus is a natural nystagmus that keeps the sensory cells of the eyes from tiring. It is the most common type of nystagmus. It happens all the time, to all of us. This type of nystagmus produces extremely minor tremors or jerks of the eyes. These tremors are generally too small to be seen with the naked eye. Physiological nystagmus will have no impact on our (NHTSA) Standardized Field Sobriety Tests, because its tremors are generally invisible.

Gaze Nystagmus occurs as the eyes move from the center position. Gaze nystagmus is separated into three types:

(1) Horizontal Gaze Nystagmus occurs as the eyes move to the side. It is the observation of the eyes for Horizontal Gaze Nystagmus that provides the forst and most accurate test in the Standardized Field Sobriety Test battery. Although this type of nystagmus is most accurate for determining alcohol impairment, its presence may also indicate the use of other drugs.

(2) Vertical Gaze Nystagmus (VGN) is an involuntary jerking of the eyes (up and down) which occurs when the eyes gaze upward at maximum elevation. The presence of this type of nystagmus is associated with high doses of alcohol for that individual and certain other drugs. The drugs that cause Vertical Gaze Nystagmus are the same ones that cause horizontal Gaze Nystagmus.

Note: There is no drug that will cause Vertical Gaze Nystagmus that does not cause Horizontal Gaze Nystagmus. If Vertical Gaze Nystagmus is present and horizontal Gaze Nystagmus is not, it could be a medical condition.

(3) Resting Nystagmus is referred to as a jerking of the eyes as they look straight ahead. Its presence usually indicates a pathology or high doses of a Dissociative Anesthetic drug such as PCP. If detected, take precautions.  (Officer Safety)

Nystagmus Resulting from Pathological Disorders: NHTSA Manual 2006

Nystagmus can be caused by certain pathological disorders. They include brain tumors and other brain damage or some diseases of the inner ear. These pathological disorders occur in very few people and in even fewer drivers.