The "pen test" for eyes, more accurately known as the Horizontal Gaze Nystagmus (HGN) test, is a field sobriety test used to assess involuntary eye movements.
Understanding Horizontal Gaze Nystagmus
The core of this test involves observing nystagmus, an involuntary jerking or bouncing of the eyes. In the case of HGN, the eye movement is side-to-side or horizontal. This phenomenon can be exaggerated by certain substances, particularly alcohol, but also other conditions.
How is the HGN test Conducted?
During the HGN test, a law enforcement officer or medical professional will typically:
- Ask the person to follow a moving object, such as a pen, a fingertip, or a small light.
- The object will be moved slowly and smoothly from side to side.
- The examiner will then observe the person's eyes for:
- Lack of Smooth Pursuit: Healthy eyes will follow the object smoothly; impaired eyes may exhibit a jerky or bouncing movement.
- Distinct Nystagmus at Maximum Deviation: The point where the eyes are turned fully to the side, nystagmus will be more pronounced if impairment is present.
- Onset of Nystagmus Prior to 45 Degrees: If nystagmus occurs before the eye is turned 45 degrees to the side it indicates a possible substance-related impairment.
Significance of the Test
The HGN test can be an indicator of impairment and is often used in roadside sobriety checks. However, it should be noted that:
- Nystagmus can occur for reasons other than substance use.
- Other medical conditions can also cause nystagmus.
- The test is not conclusive on its own and other tests are usually included in a full sobriety assessment.
| Component | Description |
|---|---|
| Test Name | Horizontal Gaze Nystagmus (HGN) Test |
| What it Measures | Involuntary side-to-side eye movement |
| How it's Conducted | Following a moving object (pen, finger, light) while observing eye movement |
| Key Signs | Jerky tracking of the object, nystagmus at maximum deviation, onset of nystagmus before 45 degrees |
| Indications | Possible substance impairment, but other conditions can also cause nystagmus |
In short, the "pen test" for eyes, or HGN test, assesses the involuntary horizontal movements of the eye when following a moving object.
