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High Eyes: How Pupil Size Can Determine The Type of Substance Someone is Using

Lori Minor MSN, MHSA, RN

Medically reviewed by

Lori Minor, MHSA, MSN, RN

February 4, 2019

Drugs and alcohol can affect all aspects of a person’s body, even their eyes. The size of the pupils and their reaction time, when exposed to light, can assist in determining the type of substance that an individual may be using.

Drugs and alcohol can make someone behave and even look different than usual. Ever seen a not-so-flattering picture of you or a friend after a night of too many drinks? The droopy face appearance, complete with exaggerated blushing and watery eyes doesn’t exactly present itself as the potential for the ultimate selfie experience.

And gazing into the glossed-over, bloodshot eyes is what gives it all away. Did you know that the size of a person’s pupils can assist in revealing the type of drug he or she has been indulging in?

Look no further for an article that explains how the little black dot at the center of your eye tells more truth than you ever wanted to divulge.

How It All Begins – Drug Classification Evaluation

When a police officer makes a traffic stop, if potential drug use is in question, the officer might decide to do an extensive check called a Drug Classification Evaluation (DCE). In this case, an expert will be present in assisting the officer with this check.

An officer certified to perform this check has completed a program that has officially tagged him or herself as a Drug Recognition Evaluator (DRE). The DRE joins the arresting officer proceeds with a list of tests for the officer who made the arrest and the arrested individual. The process actually involves a whopping 12 steps, including:

  • Alcohol breath test
  • Evaluator interviews officer who performed an arrest, asks questions about arrest and decision to have DCE performed
  • The distinction between potential drug use or health problem is made
  • Eye gaze examination performed
  • Divided attention test (one-leg stand, finger to nose, etc.)
  • Pulse rate, body temp, and blood pressure is taken
  • Evaluation of pupils in various lighting
  • Checks muscle tone
  • Checks muscle tone further & takes pulse again
  • Determination made & interview about substance abuse given to an arrested individual
  • Physical and mental condition assessed; determination of the potential type of substance in use
  • Blood or urine specimen is obtained

For the purpose of discovering more about what pupils tell the evaluator, we will focus on number seven.

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Scoping Out A Pupil – Size, And Dilation

There are a few methods and a particularly helpful gadget that allow an officer to size up a person’s pupils.

First, different forms of lighting are helpful. Evaluators are trained to check out eyeballs in dark light, room light, and direct light.

Next, officers use a bit of advanced technology called a pupillometer—actually just a ruler-shaped extension dotted with black circles of various diameters. The dots range from small to large, and the officer simply holds the rectangular device next to a suspect’s eye to compare real pupil to printed circle.

Finally, an evaluator notes the reaction time of the pupil. As a beam of light is extended to reach the eye or when brightness is removed, the officer observes how the pupil takes shape during the transition.

Pupils normally have a quick reaction time, but persons under the influence of a substance often have a sluggish pupil. Like a toddler testing the boundaries of independence, a pupil on drugs rebels against constriction. If the pupil does decide to shrink, it does so slowly.

Clinical research conducted on a group of non-drug users determined that a pupil should not constrict below 3.0 mm, nor dilate to a diameter of more than 6.5 mm. The results were consistent through a multitude of factors, including lighting levels and iris colors.

More Than Meets The Eye

Although you might have a hankering to rush to the nearest bathroom with a flashlight, checking pupils is just one step in the ladder of evaluation. The size of pupils alone doesn’t tell it all. Once the extensive 12-step test is completed by a drug recognition evaluator, an educated determination about what type of substance may have been used would be noted. The ultimate proof is in the pudding: The blood or urine test is given at the end of the evaluation is what feeds the officers the precise information about the substance(s) present in a suspect’s system.

Being Evaluated

Getting pulled over isn’t what normal people include in their ideal night on the town. But sometimes, serious situations happen that make a person realize he or she has a problem. Some people are caught when pulled over for a routine traffic violation. Others might have visibly chaotic driving or obviously delayed reactions prior to being stopped by the cops. Any experience like this can shake someone to the core, but reflecting on being caught with a drug in your system is the most riveting thought of all. The consideration of this probably makes you realize that things are getting out of control.

Seeking Help For Drug Abuse Or Addiction

When the safety and well-being of others are called into question, it is time to get help. Drug or alcohol addiction can easily start to dominate a person’s life, behavior, thoughts, physical health, and even emotions. Waiting until an issue has snowballed is not what you want to allow infiltrate your life or the lives of those you love.

It is necessary to take immediate action to ensure that you are making a decision that is beneficial for your future. Contact a professional now by reaching out to us at We can assist you in getting you or a loved one of the rehabilitation that everyone suffering from addiction deserves.

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