Which eyes are evaluated during the HGN test?

The HGN test is specifically designed to assess nystagmus, which is an involuntary eye movement that can indicate impairment, particularly in relation to alcohol consumption or drug influence. During the test, both the left and right eyes are evaluated simultaneously to provide a comprehensive look at the eye movements and to compare any differences in how they react. By evaluating both eyes, the examiner can determine the presence and severity of HGN, which is crucial for assessing a person's level of impairment. This thorough assessment helps ensure that the evaluation is accurate and reliable, as nystagmus can vary between eyes. Therefore, the focus on both eyes allows for a proper diagnosis based on the observed reactions.