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Horizontal Gaze Nystagmus

Interviewer: Let’s talk about some of the tests themselves and explore that territory of the standardized field sobriety. What would be the first one that we could talk about?

Ron Mondello: One of the most popular is the HGN that we referred to before, the Horizontal Gaze Nystagmus. Nystagmus, in and of itself, is defined as an involuntary jerking of the eye. Alcohol and certain other drugs will cause HGN, this involuntary jerking of the eye.

Nystagmus Can Be Found in People With Brain Damage, Tumors or Some Diseases of the Inner Ear

Interviewer: Can something else cause that, besides alcohol or drugs? If someone has eye problems or contact lenses that are weird, can that also cause those kind of things?

Ron Mondello: I’ve never heard about contact lenses, but I would imagine that is a possibility. You will find nystagmus in folks that have brain tumors or other brain damage or some diseases of the inner ear. It occurs in very few people and of course in even fewer drivers, but it certainly can exist, yes.

It is the observation of the eyes for this HGN that provides the first and the most accurate test in the standardized field sobriety test battery, although, again, this type of nystagmus is the most accurate for determining alcohol impairment. Its presence may also indicate the use of certain types of drugs.

Let’s just briefly talk about the clues, because there is no pass or fail with the field sobriety tests. There are clues that the police officer will record and then make a determination as to whether or not he believes you are impaired and that there’s probable cause to take you down to the police station to administer the Breathalyzer.

Prior to a Police Officer Administering the HGN, He’s Got to Check Your Eyes to Make Sure That Your Pupil Size is Equal

Prior to a police officer administering the HGN, he’s got to check your eyes to make sure that your pupil size is equal, because if one pupil is much smaller than the other, that may be an indication that there is a medical problem and perhaps one of the ones that we just spoke about, like there may be a brain tumor or some brain damage or some other disease or something wrong with the eyes.

So the first thing he does is check to see if the pupils are of equal size. He’ll do something else called “equal tracking.” Basically, that is to see that both eyes can follow an object together. If the eyes don’t track together, or if the pupils are noticeably unequal in size, then there’s a high probability or chance that there’s a medical disorder or an injury.

Now, when we say tracking together, basically, like a marble rolling across the table and your eyes were to follow that, your left and right eye should move. If only one of those eyes moves as opposed to the other, then there’s an indication that there’s something else wrong.

We already spoke that this HGN is an involuntary jerking of the eyes. That occurs as the eyes gaze toward the side or move towards the side and some jerking of the eye will be seen if the eyes are moved far enough to the side.

Now, there are a couple of clues that they look for. The first one is called “lack of smooth pursuit.” That’s clue number one. The eyes can be observed to jerk or bounce as they follow a smoothly moving stimulus. You know what that stimulus typically is? Just a pen. He pulls it out of his pocket. It may be a penlight. It’s nothing sophisticated.

The Eyes of an Unimpaired Person Follow the Pen Smoothly

The eyes of an unimpaired person would follow smoothly. Again, just like a marble rolling across a smooth piece of glass or like windshield wipers moving across a wet windshield. If that doesn’t occur and there is this lack of smooth pursuit, with a jerk or bounce, then that’s clue number one.

Clue number two is entitled “distinct and sustained nystagmus at a maximum deviation.” That’s a lot of words. It seems complex, but it really isn’t. Basically, what this clue number two stands for is when the eye is held at a maximum deviation to either the left or the right for four seconds, people will exhibit a slight jerking of the eye at that maximum deviation even when they’re unimpaired. This will not be evident or sustained for more than a few seconds.

That’s why the police officer will hold your eye at that maximum deviation, that maximum distance, for at least four seconds so that when impaired by alcohol, that jerking will be larger and more pronounced and sustained for more than the four seconds.

The third clue is the point at which the eye is first seen jerking. It’s called the “onset of nystagmus prior to 45 degrees,” and that’s the third clue. What happens is if the jerking of your eye begins prior to 45 degrees, it’s evident that the person has a BAC above a 0.08. Again, you take the pen. They move it about 12 to 15 inches away from your face, and it is moved to the left and to the right at a 45 degree angle.

The Police Officer Looks for Three Things During The Administering of The HGN

The police officer will look for those three clues that we’ve just mentioned, and he’ll record those clues. Here are some of the things that he looks for: the eye can’t follow a moving object smoothly. That’s number one. The nystagmus is distinct and sustained when the eye is held at a maximum deviation for a minimum of four seconds. Then number three is what the angle of onset of nystagmus is prior to the 45 degrees.

Those are the three clues that the police officer will record, and it’s a very accurate test that alerts the police officer, if those three clues are present, that you are probably impaired due to alcohol.

Now, again, nystagmus may be due to causes other than alcohol, and these other causes include seizure medications and some other drugs. If there is a large disparity between the performance of the right and the left eye, that may also indicate a medical condition.

The HGN is Always Administered While the Subject is in a Standing Position

Interviewer: As far as the HGN goes, for the record, is that performed while the individual is standing or sitting down?

Ron Mondello: I can tell you that, in New Jersey, I have never once come across a defendant that was asked to sit down during HGN. From my experience, 100% of the cases, and I’ve had hundreds, always involve the defendant standing.

Interviewer: Are they always asked beforehand, or do they just kind of start performing this exercise immediately? In other words, does the police officer go to the window and start saying, “I’m going to perform a particular test right now, so if you consent to this, I’ll go ahead and begin”?

Ron Mondello: Well, after you get pulled over, the officer will say, “Give me your credentials.” A conversation will occur between the driver and the police officer. The first clue is the odor of alcohol and then bloodshot eyes. He’ll also be looking to see if you’re fumbling as you’re trying to get your credentials. If all three of those are present, there’s a very high probability the police officer will ask you to step out of the car. That’s when he’ll speak to you about conducting the field sobriety tests.

Interviewer: Do other factors ever come into play when it comes to that particular test, like maybe bright lights coming from the police officer’s car or just the reflections of oncoming vehicles?

Ron Mondello: Typically, the police officer will move you away from any bright lights. That’s not going to change the nystagmus. It will shrink your pupils if you’re speaking to him and bright lights are shined on your eyes, but they will typically move you away from any lights. Overhead lights that are on the street are not going to affect the size of your pupil. Your eyes have already adjusted.

The officer will take some precautions before he conducts that test.

By Ronald P. Mondello