Horizontal Gaze Nystagmus (HGN)
What it is and what causes it
Horizontal gaze nystagmus is an involuntary jerking of the eyes that impairs vision and focus. While often associated with drunk driving, HGN can have other causes like fatigue or medication side effects.
- Nystagmus means the eyes jerk back and forth repeatedly.
- Horizontal gaze nystagmus (HGN) means the eyes jerk side to side.
- Drinking too much alcohol can cause HGN.
- Police use HGN tests to detect drunk driving.
What Causes HGN?
- Drinking a lot of alcohol in one sitting causes HGN.
- Alcohol impairs the nervous system’s control of eye movements.
- Stress, tiredness, and some drugs can also trigger HGN.
- People often don’t realize they have HGN.
What Does HGN Look Like?
- Eyes jerk uncontrollably side to side.
- Hard to focus on one thing because of eye jerking.
- Other drunk symptoms may happen too like slurred speech.
- With fatigue, may also have dizziness and moodiness.
HGN and Field Sobriety Tests
- Police use field tests if drunk driving is suspected.
- Drivers must do simple focused tasks like walk a line.
- If unable to focus, likely also unsafe to drive.
- HGN test checks for eye jerking and focus issues.
How the HGN Test is Done
1. Driver faces away from lights and distractions.
2. They remove any eyeglasses.
3. Officer says they will check the eyes.
4. Officer moves pen 12–15 inches in front of face.
5. Driver follows pen side to side with eyes.
6. Officer watches eyes for jerking and focus issues.
Clues for HGN
- Lack of smooth pursuit (eyes jerk following pen)
- Sustained jerking at maximum side gaze
- Jerking before 45 degrees gaze
- If jerking occurs, officer confirms HGN for 4 seconds.
- HGN test is part of overall sobriety assessment.
Other Types of Nystagmus
- Can be present at birth or acquired later.
- Can move up/down or in circles.
- See doctor if you have symptoms like:
- Tilting head to see
- Shaking vision
- Light sensitivity
- Dizziness
- An eye exam can check for serious conditions causing it.
Anyone experiencing uncontrollable horizontal eye movements should be evaluated by an eye doctor. Proper diagnosis of the underlying cause of HGN can help treat the condition and restore normal eye function. Left untreated, persistent nystagmus can seriously impact day-to-day activities and quality of life.
Being aware of HGN symptoms and seeking medical advice can help correct this disruptive condition.
References:
A resource guide describes the science and the law about horizontal gaze nystagmus. National Highway Traffic Safety Administration. Accessed December 2022.
Horizontal gaze nystagmus (HGN) sobriety test: Is it reliable? Driving Laws by Nolo. Accessed December 2022.
DWI detection and standardized field sobriety testing (participant manual). National Highway Traffic Safety Administration. February 2018.
Horizontal gaze nystagmus: How it works/how to challenge and exclude it. National College for DUI Defense. December 2017.
