Nystagmus Test

What is a Nystagmus Test?

A Nystagmus Test, also known as the Horizontal Gaze Nystagmus (HGN) Test, is a standard field sobriety test utilized by law enforcement officers during DUI arrests to assess alcohol impairment. This test focuses on involuntary jerking of the eyes, called horizontal gaze nystagmus, which can indicate alcohol impairment.

During the test, the police officer observes the suspect's eyes as they track a moving object horizontally. The officer looks for three clues: lack of smooth pursuit, the distinct onset of nystagmus before maximum deviation, and the onset of nystagmus before 45 degrees. These clues suggest impairment due to alcohol consumption.

Nystagmus is a medical term for involuntary, rapid, and jerking eye movements. Various factors, including inner ear disorders, head injuries, or medical conditions, can cause it. The HGN test specifically targets the horizontal gaze nystagmus test, where the eyes exhibit jerking movements as they reach the maximum deviation.

For accurate assessment, the test requires standardized procedures and careful observation by the police officer. Equal tracking and equal pupil size are essential factors to consider during the test, ensuring reliable results.

Although the HGN field sobriety test often provides valuable evidence for determining probable cause during a DUI arrest, it is not conclusive proof of alcohol impairment on its own. Other standardized field sobriety tests may be conducted to corroborate the findings.

Why is a Nystagmus Test performed?

A Nystagmus Test is performed primarily by law enforcement officers during DUI (Driving Under the Influence) investigations to assess potential alcohol impairment in suspects. The test is one of several standardized field sobriety tests utilized to determine whether a driver is under the influence of alcohol or drugs.

The primary purpose of the Nystagmus Test is to detect involuntary jerking of the eyes, known as nystagmus, which can be indicative of alcohol impairment. By observing the suspect's eyes as they track a moving object horizontally, the police officer looks for specific clues that suggest impairment. These clues include:

• Lack of smooth pursuit: The eyes' inability to track a moving object smoothly.
• Distinct nystagmus at maximum deviation: Jerking of the eyes when they reach their maximum deviation to the side.
• The onset of nystagmus before 45 degrees: The appearance of nystagmus before the eyes reach a 45-degree angle from the center.

These clues, when observed during the test, may indicate impairment due to alcohol consumption. However, it's important to note that the Nystagmus Test is not conclusive proof of impairment. It serves as one component of the DUI investigation process and is often used in conjunction with other field sobriety tests and evidence gathered by law enforcement officers.

What are the different types of Nystagmus Tests?

Several types of nystagmus tests are used in various contexts, including medical examinations, neurological assessments, and DUI investigations by law enforcement officers. Some of the critical types include:

• Clinical nystagmus examination: This involves a comprehensive nystagmus assessment by medical professionals. It may include various maneuvers such as the Dix-Hallpike maneuver, caloric testing, and examination of eye movements in different gaze positions.
• HGN test: This field sobriety test is commonly used by law enforcement officers during DUI investigations. It focuses on detecting horizontal nystagmus, indicating alcohol impairment when certain clues are observed during eye tracking.
• Vertical: Similar to the HGN test, this evaluates nystagmus in the vertical plane. It may be used with other tests to assess neurological conditions or intoxication.
• Resting nystagmus examination: Observing nystagmus when the eyes are at rest, without any external stimulus. Resting nystagmus can occur due to various medical conditions or neurological disorders.
• Smooth pursuit test: This evaluates the ability of the eyes to track a moving object smoothly. Impaired smooth pursuit may indicate dysfunction in the ocular motor system.
• Maximum deviation test: This part of the HGN test involves observing nystagmus when the eyes reach their maximum deviation to the side. Jerking movements at this point can be indicative of alcohol impairment.
• Sustained: Observing nystagmus while the eyes remain fixed. Sustained nystagmus may occur due to certain medical conditions or drug intoxication.

These tests serve different purposes and are conducted under various circumstances, from medical examinations to forensic investigations. Each type of nystagmus test requires specific expertise and interpretation by qualified professionals to accurately assess the presence and characteristics of the medical condition of nystagmus and its underlying causes.

How is a Nystagmus Test conducted, and how does it work?

A Nystagmus Test, commonly used in DUI investigations, is conducted as follows:

1. Initial assessment: The law enforcement officer introduces themselves and explains the test's purpose to the suspect. They may also inquire about relevant medical conditions or factors affecting the test.
2. Positioning: The suspect is asked to stand with their feet together and arms at their sides, maintaining their balance.
3. Eye examination: The officer instructs the suspect to follow a stimulus, typically a pen or flashlight, as it moves horizontally across their field of vision. The stimulus should be positioned approximately 12-15 inches away from the suspect's nose and moved smoothly at a steady speed.
4. Observation: While the suspect tracks the stimulus, the officer carefully observes the suspect's eyes for specific clues of nystagmus:
5. Lack of smooth pursuit: The eyes should smoothly track the stimulus. It indicates a lack of smooth pursuit if they exhibit jerky or erratic movements.
6. Distinct nystagmus at maximum deviation: Any jerking movements are noted when the eyes reach their maximum deviation to the side.
7. The onset of nystagmus before 45 degrees: If nystagmus (jerking movements) begins before the eyes reach a 45-degree angle from the center, it indicates impairment.
8. Repeat for another eye: The test is repeated for the other eye to ensure consistency and accuracy.
9. Interpretation: Based on the observations, the officer determines whether the suspect exhibited any of the three clues associated with nystagmus. The presence of these clues may suggest impairment due to alcohol consumption.
10. Additional tests: Depending on the outcome of the Nystagmus Test and other factors, the officer may conduct additional field sobriety tests or chemical tests to gather further evidence of impairment.

What are the typical findings from a Nystagmus Test?

During a Nystagmus Test, which includes the Horizontal Gaze Nystagmus (HGN) Test commonly used in DUI investigations, several typical findings may be observed:

• Smooth pursuit: In individuals not under alcohol, the eyes smoothly track a moving object without jerking or hesitation.
• Lack of smooth pursuit: Impaired individuals may exhibit difficulty smoothly tracking the stimulus, with jerky or erratic movements of the eyes.
• Distinct nystagmus at maximum deviation: Involuntary jerking movements may be observed when the eyes reach their maximum deviation to the side. This is particularly notable if it occurs before the eyes get a 45-degree angle from the center.
• The onset of nystagmus before 45 degrees: Nystagmus (jerking movements) that begins before the eyes reach a 45-degree angle from the center is considered an indication of impairment.
• Unequal tracking: The eyes of an impaired individual may exhibit differences in their ability to track the stimulus equally, with one eye showing more pronounced nystagmus than the other.
• Pupil size: An assessment of pupil size may reveal inequality, dilation, or constriction, which can also be indicative of alcohol impairment or other medical conditions.
• Inability to maintain eye level: Impaired individuals may struggle to keep their eyes at the same level while tracking the stimulus, leading to deviations or tilting of the head.

What conditions or disorders can a Nystagmus Test help diagnose?

A Nystagmus Test, mainly when conducted as part of a comprehensive clinical examination by medical professionals, can aid in diagnosing various conditions and disorders affecting the vestibular system and ocular motor control. Some of these conditions include:

• Vestibular disorders: Nystagmus can be a prominent feature of vestibular disorders, which affect the inner ear and vestibular system responsible for balance and spatial orientation. Conditions such as benign paroxysmal positional vertigo (BPPV), labyrinthitis, and vestibular neuritis may present with nystagmus as a symptom.
• Central nervous system disorders: Nystagmus can also be associated with major nervous system disorders affecting the brainstem, cerebellum, or vestibular nuclei. Conditions such as multiple sclerosis, brainstem strokes, and cerebellar degeneration may manifest with nystagmus.
• Alcohol intoxication: In DUI investigations, the Horizontal Gaze Nystagmus (HGN) Test is used to assess alcohol impairment. Alcohol consumption can affect the vestibular system and disrupt ocular motor control, leading to nystagmus.
• Drug intoxication: Certain drugs and medications, including sedatives, tranquilizers, and anticonvulsants, can cause nystagmus as a side effect. Conducting a Nystagmus Test can help assess potential drug intoxication in clinical or forensic settings.
• Congenital nystagmus: Some individuals may have nystagmus present from birth (congenital nystagmus), which may be associated with underlying genetic or developmental abnormalities affecting the visual system or brain pathways.
• Neurological disorders: Various neurological conditions, such as epilepsy, traumatic brain injury, and brain tumors, can result in nystagmus due to disruptions in neural pathways controlling eye movements.
• Vision disorders: Nystagmus may occur secondary to vision disorders, such as strabismus (misalignment of the eyes) or refractive errors. In such cases, nystagmus may be a compensatory mechanism to optimize visual acuity.