Why is it important to maintain a sufficient distance between the officer and the subject during the test?

Maintaining a sufficient distance between the officer and the subject during the Horizontal Gaze Nystagmus (HGN) test is crucial for observational accuracy. This distance allows the officer to clearly see the subject's eye movements, which is vital in assessing the presence of nystagmus—a condition that can indicate impairment due to alcohol or drugs. If the officer is too close, it may hinder their ability to perceive subtle movements accurately, potentially affecting the validity of the test results. Observing the eyes at an appropriate distance ensures that the officer can detect the onset of nystagmus at 45 degrees, as well as note any other involuntary eye movements that may occur. Therefore, the clarity of observation directly impacts the reliability of the HGN as an indicator of impairment.