close up photo of a person's eyes

Why Do The Police Pay Attention to the Driver’s Eyes During Traffic Stops?

The eyes are the window to the soul. When it comes to a DUI stop, they can also be evidence. Let’s discuss how the appearance of your eyes can affect your traffic stop.

Eyes and Impairment

Substances like drugs and alcohol can affect the way our eyes appear and function. Both of these causes can lead to a DUI investigation and arrest.

When under the influence of drugs or alcohol, people may experience side effects like blurred vision, double vision, or even hallucinations. If individuals are experiencing these effects while driving, it will likely affect how they operate and maneuver their vehicle . If the police notice a driver moving erratically, they will probably pull them over for further investigation.

Additionally, an individual’s eyes may appear different if they are under the influence of drugs or alcohol. They may have:

  • Dilated pupils
  • Red or bloodshot eyes
  • Heavy eyelids
  • Glossy eyes

These visual differences are why the police will look closely at a driver’s eyes during a traffic stop. However, these abnormalities are not always caused by impairment. There are a number of reasons why someone may have unusual-looking eyes that have nothing to do with alcohol or drugs.

For example, individuals may be suffering from eye issues due to:

  • Allergies
  • Pink eye
  • Dry eyes
  • Contact lens irritation
  • An infection
  • Tiredness
  • A reaction to a medication
  • Adrenaline

As you can see, the appearance of one’s eyes cannot simply be attributed to drug or alcohol impairment.

Horizontal Gaze Nystagmus Test

There is one type of standardized field sobriety test that focuses directly on the driver’s eyes. The horizontal gaze nystagmus (HGN) test is used as a method to collect evidence during a DUI stop.

During this examination, the police move an object (typically a pen) from side to side in front of the driver’s face. The driver is instructed to only follow the object with their eyes and not move their head.

The main things that the officer looks for during this test include:

  • If the driver can follow the object smoothly
  • If the eyes are jerking when held at one side
  • If the eyes jerk before the object is 45 degrees from the center of their face

If the driver appears to have jerky eye movements or otherwise struggles with this test, the officer may count it as a failure and use this evidence to support their claim that the driver was driving while under the influence.

Like how eyes may appear unusual for reasons other than impairment, the same is true for HGN test performance. Individuals may be unable to pass this test for a number of reasons, even if they are completely sober. For example, underlying medical conditions or recent medical problems can inhibit how smoothly the driver may follow the moving object.

How Reliable is the HGN Test?

There is a lot of discussion about how reliable the horizontal gaze nystagmus test is when introduced as evidence of DUI.

HGN tests have an accuracy rate of about 77%. Of the three standardized field sobriety tests, HGN tests have the highest accuracy rate. If the driver takes field sobriety tests during their DUI stop, they could be asked to take all three tests: the HGN test, the walk and turn test, and the one-leg stand test. When all three are taken, they are accurate about 82% of the time.

82% is not good enough when someone is being charged with a criminal offense. Based on this accuracy rate, there are numerous reasons why these unreliable tests should be challenged after a DUI arrest.

Can I Refuse the HGN Test in Wisconsin?

Yes - drivers can and should refuse to take the horizontal gaze nystagmus test, as well as all other field sobriety tests. Drivers face no legal consequences for refusing these tests. Sadly, not enough drivers are aware of their legal right to refuse and end up taking these tests, only to fail for slight mistakes and end up with a DUI charge.

Wisconsin’s Most Successful DUI Defense Firm

If you were recently charged with DUI in the Sheboygan area, contact our attorneys at Melowski & Singh, LLC. We focus solely on DUI so we can provide the strongest possible defense for our clients. Call us today at (920) 294-1414 to discuss your charges with our attorneys.