October 29, 2015

DWI Detection and Standardized Field Sobriety Testing • Jerking of the eyes as they look straight ahead

Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Jerking of the eyes as they look straight
ahead
Presence usually indicates a pathological
disorder or high doses of a Dissociative
Anesthetic drug such as PCP
If detected, take OFFICER SAFETY
precautions
Resting Nystagmus
8-27
Resting Nystagmus is referred to as a jerking of the eyes as they look straight ahead. Its
presence usually indicates a pathological disorder or high doses of a Dissociative
Anesthetic drug such as PCP. If detected, take precautions. (OFFICER SAFETY.)
Nystagmus may also 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.
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Brain tumors and other brain damage
Some inner ear diseases
Rare in the driving population
Pathological Disorder Nystagmus
8-28
Nystagmus may also 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.
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HS 178 R5/13 17 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Equal pupil size
Resting nystagmus
Equal tracking
Medical Impairment
8-29
Medical Impairment
The examinations that you conduct to assess possible medical impairment include:
• Equal pupil size
• Resting nystagmus
• Equal tracking
Pupil size will be affected by some medical conditions or injuries. If the two pupils are
distinctly different in size, it is possible that the subject:
• Has a prosthetic eye
• Is suffering from a head injury
• Has a neurological disorder
Resting nystagmus is referred to as jerking as the eyes look straight ahead. This
condition is not frequently seen. Its presence usually indicates a pathology or high
doses of a drug such as a Dissociative Anesthetic like PCP.
Resting nystagmus may also be a medical problem.
Tracking ability will be affected by certain medical conditions or injuries involving the
brain.
This observation is a medical assessment. If the two eyes do not track together, the
possibility of a serious medical condition or injury is present.
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HS 178 R5/13 18 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Even though the possibility of alcohol
and/or drug impairment exists, be aware of
medical conditions having symptoms in
common with alcohol influence.
Medical Impairment (Cont.)
8-30
By passing a stimulus across both eyes, you can check to see if both eyes are tracking
equally. If they don't (i.e., if one eye tracks the stimulus, but the other fails to move, or
lags behind the stimulus) there is the possibility of a neurological disorder.
If a person has sight in both eyes, but the eyes fail to track together, there is a possibility
that the person is suffering from an injury or illness affecting the brain.
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Check eyes for:
Equal pupil size
Resting nystagmus
Equal tracking
If eyes do not track together, or pupils are
noticeably unequal in size, medical disorders
or injuries may be present
HGN Medical Impairment
Assessment Procedures
8-31
Procedures to Assess Possible Medical Impairment
Prior to administration of HGN, the eyes are checked for equal pupil size, resting
nystagmus, and equal tracking (can they follow an object together). If the eyes do not
track together, or if the pupils are noticeably unequal in size, the chance of medical
disorders or injuries causing the nystagmus may be present.
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HS 178 R5/13 19 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Lack of smooth pursuit
Distinct and sustained Nystagmus at
maximum deviation
Onset of Nystagmus prior to 45 degrees
HGN Testing: Three Clues
8-32
Procedures of Horizontal Gaze Nystagmus Testing: The Three Clues
The test you will use at roadside is "Horizontal Gaze Nystagmus" -- an involuntary
jerking of the eyes occurring as the eyes gaze to the side. When a person is impaired
by alcohol or certain drugs, some jerking will be seen if the eyes are moved far enough
to the side.
• The Lack of Smooth Pursuit (Clue Number One) - The eyes can be observed to jerk or
"bounce" as they follow a smoothly moving stimulus, such as a pencil or penlight. The
eyes of an impaired person will not follow smoothly, i.e., a marble rolling across sand
paper, or windshield wipers moving across a dry windshield.
• Distinct and Sustained Nystagmus At Maximum Deviation (Clue Number Two) -
Distinct and sustained nystagmus is evident when the eye is held at maximum
deviation for a minimum of four seconds and continues to jerk toward the side.
• Onset of Nystagmus Prior To 45 Degrees (Clue Number Three) - The point at which
the eye is first seen jerking. If the jerking begins prior to 45 degrees it is evident that
the person has a BAC above 0.08, as shown by recent research.
The higher the degree of impairment, the sooner the nystagmus will be observable.
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HS 178 R5/13 20 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Check for eyeglasses
Verbal instructions
Position stimulus (12-15 inches and slightly above
eye level)
Check for equal pupil size and resting nystagmus
Check for equal tracking
Lack of smooth pursuit
Distinct and sustained nystagmus at maximum
deviation
Onset of nystagmus prior to 45 degrees
Total the clues
Check for vertical nystagmus
Administrative Procedures
8-33
Horizontal and Vertical Gaze Nystagmus can be observed directly and does not require
special equipment. You will need a contrasting stimulus for the subject to follow with
their eyes. This can be a penlight or pen. The stimulus used should be held slightly
above eye level, so that the eyes are wide open when they look directly at it. It should
be held approximately 12 - 15 inches in front of the nose. Remain aware of your position
in relation to the subject at all times.
• Check for eyeglasses
• Verbal instructions
• Position stimulus (12-15 inches and slightly above eye level)
• Check for equal pupil size and resting nystagmus
• Check for equal tracking
• Lack of smooth pursuit
• Distinct and sustained nystagmus at maximum deviation
• Onset of nystagmus prior to 45 degrees
• Total the clues
• Check for vertical nystagmus
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Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
1. Check for eyeglasses
HGN Procedures
8-34
Administrative Procedures for Horizontal Gaze Nystagmus
It is important to administer the Horizontal Gaze Nystagmus test systematically using
the following steps, to ensure that nothing is overlooked.
There are 10 steps in the systematic administration of the Horizontal Gaze Nystagmus
test.
Step 1: Check for Eyeglasses.
Begin by instructing the subject to remove eyeglasses, if worn.
It does not matter whether the subject can see the stimulus with perfect clarity, as long
as subject can see it at all.
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HS 178 R5/13 22 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
1. Check for eyeglasses
2. Verbal instructions
3. Position stimulus
HGN Procedures (Cont.)
8-35
Step 2: Verbal Instructions.
Give the subject the appropriate verbal instructions:
Point out that officers’ should note whether subject sways, wobbles, etc. while trying to
balance.
• Put feet together, hands at the side
• Keep head still
• Look at the stimulus
• Follow movement of the stimulus with the eyes only
• Keep looking at the stimulus until told the test is over
Step 3: Position the Stimulus.
Position the stimulus approximately 12 - 15 inches (30 - 38 cm) in front of subject's
nose, and slightly above eye level to commence the test.
Resting Nystagmus may be observed at this time. Officers should note whether the
subject displays Resting Nystagmus.
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HS 178 R5/13 23 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
4. Pupil size and resting nystagmus
5. Equal tracking
HGN Procedures (Cont.)
8-36
Step 4: Equal Pupil Size and Resting Nystagmus. Check for equal pupil size and
resting nystagmus.
Step 5: Equal Tracking.
Check for equal tracking. Move the stimulus rapidly from center to far right, to far left
and back to center.
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
6. Check for lack of smooth pursuit
7. Check for distinct and sustained
nystagmus at maximum deviation
8. Check for onset of nystagmus prior to 45
degrees
HGN Procedures (Cont.)
8-37
Step 6: Lack of Smooth Pursuit. Check the left eye for lack of the "Smooth Pursuit"
clue. If the eye is observed to jerk while moving, that is one clue.
Check the right eye for lack of the "Smooth Pursuit" clue and compare.
Step 7: Check the right and left eye for the "distinct and sustained nystagmus at
maximum deviation" clue. If the jerkiness is distinct and sustained, that is one clue.
Step 8: Onset of Nystagmus Prior to 45 Degrees. Check the left eye for the "onset of
nystagmus prior to 45 degrees" clue. If the jerking begins prior to 45 degrees, that is
one clue.
Check the right eye for "onset of nystagmus prior to 45 degrees" clue, and compare.
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HS 178 R5/13 25 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
9. Total the clues
10. Check for Vertical Gaze Nystagmus
HGN Procedures (Cont.)
8-38
Step 9: Total the clues
Maximum number of clues possible for each eye: 3
Total maximum number of clues possible for both eyes: 6.
Step 10: Check for Vertical Nystagmus
It is possible that all three clues definitely will be found in one eye, while only two (or
sometimes only one) will show up in the other eye. It is always necessary to check both
eyes, and to check them independently. Notwithstanding, it is unlikely that the eyes of
someone under the influence of alcohol will behave totally different.
Thus, if one eye shows all three clues distinctly while the other eye gives no evidence of
nystagmus, the person may be suffering from one of the pathological disorders covered
previously.
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HS 178 R5/13 26 of 62
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Look for three clues of nystagmus in each
eye:
Lack of smooth pursuit
Distinct and sustained Nystagmus at
maximum deviation
Onset of Nystagmus prior to 45 degrees
Test Interpretation
8-39
Test Interpretation
You should look for three clues of nystagmus in each eye.
Lack of Smooth Pursuit (The eye cannot follow a moving object smoothly)
Distinct and Sustained Nystagmus at Maximum Deviation (Nystagmus is distinct and
sustained when the eye is held at maximum deviation for a minimum of four seconds)
Onset of Nystagmus Prior to 45 Degrees.
Based on recent research, if you observe four or more clues it is likely that the subject's
BAC is at or above 0.08. Using this criterion you will be able to classify about 88% of
your subjects accurately. This was determined during laboratory and field testing and
helps you weigh the various Standardized Field Sobriety Tests in this battery as you
make your arrest decision.
Session 8 - Concepts and Principles of the Standardized Field Sobriety Tests (SFST)
DWI Detection and Standardized Field Sobriety Testing
Lack of smooth pursuit
Distinct and sustained nystagmus at
maximum deviation
Onset of nystagmus prior to 45 degrees
Three Clues of Horizontal Gaze
Nystagmus
8-40
When we administer the Horizontal Gaze Nystagmus test, we look for three specific
clues as evidence of alcohol influence.
We check each eye independently for each clue.
For standardization, begin with the subject's left eye. Check for the first clue. Next,
check right eye for same clue. Repeat this procedure for each clue starting with left
eye, then right eye. Compare and document the results.
When we are checking an eye, it is good practice to administer the test by the numbers
each time, to make sure that no step is overlooked.
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HS 178 R5/13 27 of 62 Source: DWI Detection and
Standardized Field
Sobriety Testing
March 2013 Edition

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