A police officer with adequate training and experience in performing the horizontal gaze nystagmus test
(HGN) may testify as to the significance of a defendant’s performance on an HGN test, according to a recent California Court of Appeal decision. Although HGN testing alone cannot determine whether a driver is under the influence of alcohol (nor determine a blood alcohol level), the HGN test is part of an officer’s total observations of a suspect. The horizontal gaze nystagmus is one basis for an officer’s opinion concerning intoxication.
A police officer can use findings from horizontal gaze nystagmus (HGN) testing as a basis for an opinion that the defendant was driving under the influence of alcohol. The prosecution is not required to submit expert testimony to confirm the officer’s evaluation of the HGN test.