Horizontal Gaze Nystagmus (HGN) is one of three National Highway Traffic Safety Administration (NHTSA) standardized field sobriety tests used for alcohol. It is also considered by the NHTSA and law enforcement to be the “silver bullet” of field sobriety tests.
The NHTSA HGN test is an alcohol test based on the NHTSA SFST studies however HGN is natural and can be visible when a person takes certain medications such as benzodiazepines or has suffered a head injury or trauma. This should be kept in mind when assessing your clients, what medication do they take (dose level) and when and why do they take it, this is extremely important since HGN is an alcohol only test.
My dissertation allowed me to conduct a literature review to research peer reviewed and non peer literature on the NHTSA HGN test outside the NHTSA. There was little to no information about the NHTSA HGN test outside NHTSA research and techniques, which is not peer reviewed and published. My recommendation for the HGN test was that it needed more research in the area of drug and or alcohol use, coupled with medical literature to assess injuries and pre-existing conditions and how they may or may not affect the test.
Feel free to take a look through the dissertation or download the complete document.