What is one limitation of using HGN testing as a sole indicator of impairment?

Using HGN testing as a sole indicator of impairment has limitations, one of which is that it does not account for medical conditions. This aspect is crucial because certain medical issues can affect a person's eye movements, potentially leading to false interpretations of impairment. For example, individuals with conditions such as certain types of inner ear disorders, neurological disorders, or even some medications affecting eye function may exhibit eye movement characteristics similar to those seen in impaired individuals. Thus, not considering these medical conditions can result in misjudgments regarding a person's true level of impairment.

This emphasizes the importance of using HGN testing in conjunction with other field sobriety tests and observations to form a comprehensive assessment of impairment.