The First of Three Field Sobriety Tests Administered By Police
The Horizontal Gaze Nystagmus Test (“HGN Test”) is the first of the three field sobriety tests often administered by police officers during OVI / DUI traffic stops.
Police officers are trained under the NHTSA Manual that nystagmus is defined as an involuntary jerking of the eyes. The NHTSA Manual further states that horizontal gaze nystagmus occurs as a subject’s eyes move to the side. Police officers are trained in the NHTSA Manual that the HGN Test is the most accurate field sobriety test for determining alcohol impairment, although it may also indicate the use of certain other drugs.
The NHTSA Manual prescribes that the HGN Test is to be administered by police officers in a uniform manner so as not to compromise the validity of the test. Generally speaking, the test is administered by moving a stimulus, such as a pen or finger, smoothly across an individual’s entire field of vision in a uniform manner while examining the individual’s eyes for clues or signs of alcohol and drug impairment.
During an OVI / DUI traffic stop, the NHTSA Manual trains police officers to use the HGN Test to look for the presence of three particular clues of impairment:
1. The Lack of Smooth Pursuit
During this portion of the HGN Test, police officers examine an individual’s eyes and observe whether the eyes jerk or bounce while following a smoothly moving stimulus. The NHTSA Manual indicates that during the administration of the HGN Test in an OVI / DUI traffic stop, the eyes of a person who is NOT impaired will be able to smoothly follow the stimulus and will look like a marble rolling across glass.
2. Distinct and Sustained Nystagmus at Maximum Deviation
During this portion of the HGN Test, police officers examine an individual’s eyes and observe whether the eyes show signs of jerking (nystagmus) when they are held at maximum deviation, or in other words, when an individual looks out to the side as far as possible without turning their head. The NHTSA manual trains police that people show signs of slight jerking of the eye at maximum deviation; however, the jerking is more pronounced when the individual is impaired by alcohol.
3. Onset of Nystagmus Prior to 45 Degrees
During this portion of the HGN Test, police officers examine an individual’s eyes and observe whether the eyes begin to show signs of jerking (nystagmus) prior to a 45-degree angle as the person follows a stimulus. The NHTSA Manual trains police officers that the higher the degree of impairment, the sooner that nystagmus will be observable prior to a 45-degree angle.
The HGN Test is the most misunderstood of the three field sobriety tests and is often baffling for jurors to comprehend in OVI / DUI trials. Prosecutors thrive on emphasizing the scientific validity of such tests in the hopes that jurors will believe the test is infallible. The reality, however, is that police officers frequently fail to administer the test in accordance with the NHTSA Manual instructions. When police officers fail to administer the test properly, the validity of the test is compromised!
Criminal defense attorney Michael Probst has handled hundreds of OVI / DUI cases and has significant experience reviewing video and audio evidence of the administration of HGN Tests by police officers during traffic stops and challenging the administration of HGN Tests at suppression hearings. A thorough and exhaustive defense of the administration of the HGN Test is crucial to every OVI / DUI case.
If you’ve been administered an HGN test and you need professional representation in your DUI case in Ohio, contact our DUI lawyer.