DUI Eye Tests - Horizontal Gaze Nystagmus

When you are stopped for suspicion of DUI, the officer may give you a DUI eye test, called the Horizontal Gaze Nystagmus or HGN. It's one of the ways police officers use to determine a driver's sobriety. You may have seen this where the officer holds a pen light up to your eye and tells you to follow it without moving your head.

One of the more popular exams is the Horizontal Gaze Nystagmus (HGN) exam. The test relies upon an officer detecting certain eye “twitching” under three test conditions:

DUI1) 45-degree angle of the eye,

2) no head motion, and

3) a stimulus for the eye to track 12-15 inches from the eye.

Officers administering the test are expected to differentiate the rapid twitching typical of a nystagmus from the normal movements of the eye. Oftentimes, that proves difficult.

In order to be considered qualified to perform the DUI eye test, or HGN exam, officers must be certified as Drug Recognition Experts (DRE). The two-week DRE program trains officers in the administration of HGN exams, as well as other detection tests. However, the International Association of Chiefs of Police reports that less than 1% of Florida officers are DRE certified. That's less than 1% of DUI stops with a proper test administrator. The lack of DRE officers creates real-world problems for the reliability of the exam. It also may cause you to have a defense to your DUI.

The National Highway Traffic Safety Administration (NHTSA) affords a mere 77% accuracy to the test. The NHTSA estimate assumes all three test conditions are met and the administrator is qualified to give the exam. In order for that estimate to be accurate, officers must conduct the exams under the same conditions as the NHTSA. Testing a driver on the side of the road is far from the same.

Furthermore, HGN exams are incredibly sensitive. Even with a properly trained officer, there are a lot of things that can trigger a false positive.

False positives can be caused by:

  • Roaring traffic,
  • Passing headlights,
  • Anything that would draw a driver's attention away from the test may be seen as HGN “twitching”.
  • A wide variety of medications
  • Head injuries
  • Irritation from contact lenses
  • Lack of sleep

Any of these signs might be read by an officer as positive for alcohol intoxication. Also, nearly everybody has some level of nystagmus that can be exaggerated by everyday conditions. Something as simple as lack of sleep can trip a false positive. An officer is expected to rule out all of these with a quick look at a driver's eye. Less than 1% of those officers are DRE 

While many law enforcement agencies claim the exam is a highly reliable test, reality says otherwise. Improper administration combined with numerous triggers for a false positive can quickly invalidate an HGN exam. Every stop is different. Every cop is different. Our DUI attorneys are familiar with the faults of the HGN exam. We can defend you from faulty tests. Call us today for a free consultation of your DUI.

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Former State Prosecutor — Tampa & Clearwater, FL 15+ Years Experience
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