What is a penlight sobriety test and how does it work?

UPDATED: Jul 18, 2023Fact Checked

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Jeffrey Johnson

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Jeffrey Johnson is a legal writer with a focus on personal injury. He has worked on personal injury and sovereign immunity litigation in addition to experience in family, estate, and criminal law. He earned a J.D. from the University of Baltimore and has worked in legal offices and non-profits in Maryland, Texas, and North Carolina. He has also earned an MFA in screenwriting from Chapman Univer...

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Mary Martin

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UPDATED: Jul 18, 2023

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UPDATED: Jul 18, 2023Fact Checked

If you were stopped at a roadside DUI checkpoint and an officer moved a penlight in front of your face and asked you to follow it with your eyes, this is the horizontal gaze nystagmus test, which is supposed to test for being under the influence of alcohol. The officer attempts to estimate the angle at which the eye begins to jerk (nystagmus is medical jargon for eye jerking); if this occurs sooner than 45 degrees, it theoretically indicates an excessive blood-alcohol concentration (BAC). The smoothness of how the eye tracks the penlight (or finger or pencil) is also a factor, as is the jerking of the eye when it is as far to the side as it can go.

This field sobriety test has proven to be subject to a number of different problems, not the least of which is that the officer is not medically trained and therefore does not have a strong ability to recognize nystagmus and estimate the angle of onset. Because of this, and the fact that the medical community does not accept the horizontal gaze nystagmus test, it is not admissible as evidence in many states. It continues, however, to be widely used by law enforcement.

Case Studies: Penlight Sobriety Test

Case Study 1: Unreliable Observations

John was pulled over by Officer Smith at a DUI checkpoint. Officer Smith conducted the penlight sobriety test and claimed that John’s eyes exhibited nystagmus before reaching the 45-degree threshold. However, John contested this observation, stating that he had no alcohol to drink that night.

Despite his claims, the officer arrested John based on the results of the test. This demonstrates the potential for inaccurate observations during the penlight sobriety test, leading to wrongful arrests.

Case Study 2: Lack of Standardized Training

Sarah was stopped by Officer Johnson, who performed the penlight sobriety test. Officer Johnson, however, had received minimal training on administering the test and was unfamiliar with the correct angle to estimate the onset of nystagmus accurately.

As a result, the test results were unreliable, yet Sarah was still arrested for DUI. This highlights the importance of standardized training for law enforcement officers to ensure the accuracy and consistency of test administration.

Case Study 3: Limited Admissibility as Evidence

Mark was subjected to the penlight sobriety test by Officer Thompson during a DUI stop. However, in Mark’s state, the horizontal gaze nystagmus test is not admissible as evidence in court due to its questionable scientific validity.

Despite the test indicating potential intoxication, the results could not be used against Mark during his legal proceedings. This raises questions about the widespread usage of a test that lacks acceptance within the medical community.

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Jeffrey Johnson

Insurance Lawyer

Jeffrey Johnson is a legal writer with a focus on personal injury. He has worked on personal injury and sovereign immunity litigation in addition to experience in family, estate, and criminal law. He earned a J.D. from the University of Baltimore and has worked in legal offices and non-profits in Maryland, Texas, and North Carolina. He has also earned an MFA in screenwriting from Chapman Univer...

Insurance Lawyer

Mary Martin

Published Legal Expert

Mary Martin has been a legal writer and editor for over 20 years, responsible for ensuring that content is straightforward, correct, and helpful for the consumer. In addition, she worked on writing monthly newsletter columns for media, lawyers, and consumers. Ms. Martin also has experience with internal staff and HR operations. Mary was employed for almost 30 years by the nationwide legal publi...

Published Legal Expert

Editorial Guidelines: We are a free online resource for anyone interested in learning more about legal topics and insurance. Our goal is to be an objective, third-party resource for everything legal and insurance related. We update our site regularly, and all content is reviewed by experts.

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