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DUI Defense
Field Sobriety Tests -
Horizontal Gaze Nystagmus
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 same.
 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 can not see the stimulus after
removing the eyeglasses they must be allowed to perform it with them on. According to the manual, hard contact lenses are to be removed so as to
avoid dislodging when the eyes are out at maximum deviation or to prevent
damage to the eyes.
The manual says not to administer the test if the suspect is wearing hard
contacts. A person with a glass eye or only vision in one eye can not be
given this test. 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. If the suspect has what is known as the lazy eye
condition, the officer is trained to test one eye while the other eye is
covered by the suspects hand, then to switch same. A person who is color
blind is not validated for this test as they will probably have a
pathological Nystagmus which is normal, and natural for that person.
Three to four percent of the general population will exhibit a
pathological Nystagmus. This can be caused by some type of neurological
disorder, brain damage, epilepsy or pathological disorder which the
suspect is born with or of unknown etiology. A large disparity between the
right and left eye can clue the officer into this problem. At an accident
scene, if the suspect sustains a concussion, this may bring on a
pathological Nystagmus thereby invalidating this test.
Although very few test conditions affect gaze Nystagmus, there are certain
administrative procedures that must be followed. As previously mentioned,
the stimulus must be placed twelve to fifteen inches in front of the
suspect's eyes. The stimulus should be held above eye level, so that the
eyes are wide open when they look directly at it. Due to narrowness of
certain individuals eyes it becomes more difficult to make a fair
evaluation of the Nystagmus unless the eyes are wide open.
If the officer believes that the Nystagmus might be there, it can not be
scored, as the benefit of the doubt must be given to the person that is
being tested. The officer is also trained to administer this test with the
suspect looking into a quiet background, away from the police cruisers
overhead. This is to avoid the probability of evaluating an induced
condition known as opto-kinetic Nystagmus. This is brought on when a
person focuses on several objects at one time or objects that are moving
away. The quiet background that is recommended is away from the view of
passing motorists. This opto-kinetic Nystagmus is a defense mechanism of
the body in order to keep the eyes from tiring. There are numerous visual
or other distractions that may impede this test. Certain environmental
factors such as wind, dust, etc. may interfere with the performance of the
Nystagmus test.
As explained earlier, Nystagmus is the involuntary jerking of the eyes. In
intoxication, three signs will often be observed. Each eye must be checked
separately. The first clue that is looked for is known as smooth pursuit.
First Clue : Lack of
Smooth Pursuit
What the officer is trained to look for is the suspect's inability to
pursue a moving stimulus smoothly while focusing that stimulus being moved
horizontally, from side to side. If the suspect moves his head to the side
at any time, the score may be invalid regardless of which clue we are
looking for. An example of what is being looked for is like a marble
rolling across a smooth pane of glass. This will be a very smooth pursuit.
If the suspect is under the influence, the eyes will bounce or jerk in
similar fashion as that same marble, but now rolled across a piece of
sandpaper. The officer is instructed to check the left eye first by moving
the object to the officer's right. The object must be moved smoothly, at a
speed of about two seconds to bring the suspect's eye as far to the side
as it can go. Any choppy or shaky hand movements or movement that is too
fast by the officer may induce a Nystagmus in the suspect's eyes and
invalidate the scoring and test. The officer is instructed to make two or
more passes in front of the eye to be absolutely certain that what they
are seeing is Nystagmus and a valid clue. If this clue is scored as
Nystagmus the suspect is assessed one point. If the suspect has this clue
emanating in one eye, it is no guarantee that it will be exhibited in the
other eye. This should be the easiest clue to see.
Second Clue: Distinct Jerkiness at Maximum Deviation
After they have checked the first eye for the smooth pursuit clue, they
must check the same eye for what is called distinct jerkiness at maximum
deviation. This is accomplished by simply moving the object to the side
until the eye has gone as far to the side as possible. At maximum
deviation, no sclera or white will be showing in the corner of the
eyeball. The officer must hold the eyeball at that position for two or
three seconds, and observe the eyeball for distinct jerkiness. The
jerkiness must be both distinct and obvious.
If the officer can not make this distinction from a slight nystagmus, the
benefit of the doubt must be given the suspect. The officer may make the
mistake of not bringing the eyes out to side as far as they can go or too
rapidly return the stimulus and incorrectly score this part of the test.
The criteria of no white showing in the corner of the eye must be met. A
Nystagmus may be incorrectly mistaken for physiological Nystagmus if the
officer does not hold the stimulus out to the side for two or three
seconds.
In approximately 50% of the suspects they encounter, a physiological
Nystagmus will be apparent when the eye initially arrives at maximum
deviation. This is due to a person not normally following an object all
the way to the side with their eyes, but turning their head to view that
object. Consequently, a certain degree of uncomfortableness is
experienced, causing a slight twitching of the eyes at this location. If
the officer brings the eyes out to the side and then immediately brings
them back, he may be scoring this physiological Nystagmus inappropriately.
Everyone has a physiological Nystagmus, but it is not visible to the naked
eye. The reason it exists is to exercise the eye muscles, lubricate them,
and prevent atrophy. Remember the jerkiness must be distinct and obvious
to be scored a point.
Final Clue : Angle of Onset
This is the most difficult to evaluate. If a suspect exhibits this clue in
one eye, the probability increases that all the other clues will be seen
as well. This does not work in reverse though. If a suspect has any of the
first two clues, it is no guarantee that the third clue will be there.
Because the 45-degree angle is a key factor in assessing a suspect's
degree of alcohol influence, it is important to know how to estimate that
angle.
The person is told to follow the stimulus until they are looking down the
45-degree diagonal. This obviously is used as practice to recognize the
angle. A rule of thumb that is being taught is in order to estimate the
45-degree angle, the stimulus must be halfway between the suspect's ear
and nose on the side being tested or just outside the shoulder area.
The estimation of this angle is critical, since studies have shown that as
the alcohol increases the angle will decrease. Although this may be the
case, this angle should not be used to estimate a specific amount of
alcohol in the bloodstream. In order to properly score this part of the
test, the officer must move the object to the 45-degree angle of gaze,
taking about four seconds. As the eye follows the object, the jerking is
looked for. If Nystagmus is observed, the stimulus is stopped and the
officer must make an observation that it is continuing at this point. If
it continues, then the officer must make sure that there is still white
showing in the corner of the eye and the angle must be estimated to be
prior than 45-degrees. If it does not, the object must continue to be
moved until the jerking does occur and continues or until the 45-degree
angle is reached. If no white of the eye is showing, the eye has either
been taken too far to the right, which would be maximum deviation that is
being evaluated, or the person has unusual eyes that will not deviate very
far to the side. The criterion of onset before 45-degrees only can be used
if some white can be seen at the outside of the eye. Too often the officer
incorrectly estimates the angle or scores this with no white showing in
the corner of the eye or both.
Ask yourself this: Can you effectively pick a 45 degree angle without
having actual lines to use as a reference point?
This test is deemed the most reliable test in determining probable cause
to believe someone is under the influence of an alcoholic beverage. This
depends on the proper administration, proper scoring, and proper training
is adhered to. Even if this be the case it is still only 77% reliable. This test should not be administered if the suspect is in a supine
position. It can be administered to them if they are sitting or standing
as long as they are erect.
At an accident scene, with a suspect lying down and this test performed,
it would be invalid due to positional alcohol Nystagmus being the cause of
the Nystagmus encountered. This is a vestibular Nystagmus that is evident
when the amount of alcohol in the vestibule system is in unequal
proportions to the amount of alcohol in the bloodstream and reacts to
gravity such as the changing position of the head.
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