Utah Criminal Defense


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Horizontal Gaze Nystagmus. Utah Field Sobriety Testing. What is it? Can I Fail the Test Sober?

Horizontal Gaze Nystagmus is one of three standard Utah field sobriety tests that officers conduct in DUI investigations.

Horizontal Gaze Nystagmus is referring to the involuntary jerking of the eyes as they move side to side. In addition to being involuntary, the DUI suspect experiencing the nystagmus is usually unaware the jerking is happening. In administering the HGN test, the officer has the subject follow the motion of a small stimulus with the eyes only. The stimulus can be the tip of a pen or penlight, or an eraser on a pencil, whichever contrasts with the background.


Utah police officers are taught to looks for clues of alcohol or drug impairment when administering a field sobriety test. HGN has 3 clues per eye and 6 clues total.

Officers are trained to always start with the DUI suspect’s left eye and then examine the right eye.

HGN CLUE 1. As the eye moves from side to side, does it move smoothly or does it jerk noticeably? The “Lack of Smooth Pursuit” is how the officer will write this clue in their DUI reports and field notes.

HGN CLUE 2. When the eye moves as far to the side as possible and is kept at that position for four seconds, does that eye jerk distinctly? This clue is written as a “Distinct and Sustained Nystagmus at Maximum Deviation” in Utah DUI reports.

HGN CLUE 3. As the eye moves toward the side, does it start to jerk prior to a 45-degree angle? “Onset of Nystagmus Prior” to 45 Degrees is another HGN clue of impairment.


(1). Imprecise Measurement. The DUI investigating officer is trying to measure a very small movement, often at night, on the side of a busy road filled with noises and lights. Police officers do not use a laser, or mechanical measuring device to see a lack of smooth pursuit or other HGN clues. In the best of conditions, determining involuntary eye jerking is subject to officer interpretation, leading to possible false positives.

(2). Suspect Height. Having the officer and DUI suspect at distinctly different heights can impair the officer’s ability to see the eye nystagmus.

(3). Field & Road Conditions. Lights, distractions, and cars on a busy interstate can impair an officer’s ability to properly conduct HGN testing or look for valid clues. Sirens, street lights, car lights, busy roads, interstates, and officer safety techniques can all play into the reliability of HGN testing.

(4). Medical Conditions. People with brain conditions, or inner ear medical problems can test positive on the HGN. Neurological disorders, unequal pupil sizes, prosthetic eyes, or unequal eye tracking can also contribute to false HGN positives.

(5). Didn’t’ Follow Procedure. All officers are trained by the National Highway Traffic Safety Administration DWI Detection and Standardized Field Sobriety Testing Manual. Officers are trained to administer the HGN test the same way every time to validate testing results, minimize false positives, and testing interpretation.

The National Highway Traffic Safety Administration DWI Detection and Standardized Field Sobriety Testing Manual states the following procedure for HGN testing:

Administrative Procedures:

1. Check for eyeglasses. Was the suspect wearing colored eye lenses that would impaired the officer’s ability to read the eyes for nystagmus? Instructed to remove eye glasses prior to testing.

2. Verbal instructions. 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.

3. Position stimulus. 12‐15 inches and slightly above eye level. Position the stimulus approximately 12 ‐ 15 inches in front of subject’s nose and slightly above eye level prior to testing. Always start with the DUI suspect’s left eye. Observe any resting nystagmus at this time.

4. Check for Equal Pupil Size and Resting Nystagmus. Is there a medical condition?

5. Check for Equal Tracking. Is there a medical condition present? Eyes should track together the test results will be impaired. Start the stimulus from center to far right, to far left, and back to center. The speed of moving the stimulus should be consistent on both eyes.

6. Lack of Smooth Pursuit.

7. Distinct and Sustained Nystagmus at Maximum Deviation.

8. Onset of Nystagmus Prior to 45 Degrees.

Failure to follow officer training can impair the HGN field sobriety test results.


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