The Horizontal Gaze Nystagmus test, or HGN, has had a tough time this year, and rightfully so. In a landmark case, People vs. McKown, the Supreme Court ruled that this mystical test had to be subjected to a rigorous legal analysis known as the Frye standard. The HGN test is used in Illinios as part of a battery of Standardized Field Sobreity tests, and is used by police officers throughout the state of Illinois to develp probable cause to arrest people.
However, the test is very, very limited. In fact, there are more than a hundred distinct causes on gaze nystagmus, and it would be a rare officer indeed who was trained to distinguish when alcohol is the only factor causing the telltale signs they are trained to examine.
After the ruling by the Supreme Court of the State of Illinois, the circuit court below determined that the test meets the standard, but imposed limitations on the general requirements for admissibility in evidence, and for its interpretation under the law. The decision was returned to the Illinois Supreme Court for futher review.
Because of those limitations, make sure your DUI attorney understands the Illinois law and protocols required for even the most limited degree of reliability of the Horizontal Gaze Nystagmus test.