Introduction

Nystagmus is a condition where one or both eyes move involuntarily. These movements are usually rhythmic and oscillatory, with the eyes moving back and forth in a repeating pattern. The movements can be side-to-side, up-and-down, or can even happen in a circular motion. They can be continuous or occur as brief episodes brought on by some trigger or an underlying condition. This can affect overall vision, the ability to gauge distance, but also balance and coordination.¹

Unlike other types of nystagmus, spontaneous nystagmus (SN) happens in the absence of any specific trigger.¹ It is important to understand the characteristics and causes of SN to achieve an accurate diagnosis, and therefore treatment.

What is Spontaneous Nystagmus?

Spontaneous nystagmus (SN) is the involuntary, rhythmic eye movements that occur in the absence of a trigger, and can happen even when a person is simply sitting or standing, and looking straight ahead without moving their head or eyes.¹ It is often caused by underlying problems in specific areas of the brain or inner ear, in which case it is referred to as pathological nystagmus, because it occurs as the result of an underlying pathology.^1,2

It is important to note that nystagmus can occasionally occur under normal, physiological conditions. For example, tracking objects (e.g., trees) while in a fast-moving car can lead to what is called optokinetic nystagmus. Similarly, vestibular nystagmus, which results from a disturbance in the inner ear’s vestibular system, can happen when someone, often a child, quickly spins around; it is simply an attempt of the body to stabilise an image when the inner ear detects a rapid motion. In both examples, this is a normal response of the body, and is called physiological nystagmus.¹

When SN is not physiological (or normal), it can either be congenital or acquired. Congenital nystagmus usually appears by 3 months of age, while acquired nystagmus would appear later in life, during adolescence or adulthood. As in cases of physiological nystagmus, SN usually is the result of an anomaly in the vestibular system, which is responsible for the control of balance, spatial orientation, and eye movement coordination. It can originate from either peripheral (the inner ear or the vestibular nerve) or central (brainstem or cerebellum) vestibular disorders.^1,3

Characteristics of Spontaneous Nystagmus

Types of movements

SN is characterised by eye movements that are rhythmic and involuntary, and can either be side-to-side (horizontal), up-and-down (vertical), or in a circular motion (torsional). The type and direction of the eye movements can help localise the lesion responsible for the symptoms.^1,2

Even though there are several ways of categorising SN, it is often classified as either “jerk” or “pendular”:⁴

• Jerk Nystagmus: The eye movements include a slow drift in one direction (slow phase), followed by a rapid corrective movement (fast phase) in the opposite direction. The direction of the fast phase is usually indicative of the site of the lesion
• Pendular Nystagmus: The eye movements are smooth, sinusoidal oscillations with even speed in both directions; there is no fast or slow phase. It is often linked to central neurological disorders such as multiple sclerosis

The direction of the eye movements can be used to describe the type of nystagmus, and it is also a key indicator of the site of the lesion responsible for SN:⁵

• Upbeat SN: There is a fast phase of the eye movements that is a rapid and repetitive jerk upwards. This is in alternance with a slow phase where the eye moves downward, before quickly snapping back up
• Downbeat SN: This is essentially the opposite of upbeat nystagmus as the eyes quickly jerk downward while the slow phase is upward

Upbeat and downbeat nystagmus are often linked to a problem originating in the brainstem or cerebellum, particularly the areas that control balance and coordination.

Symptoms

SN can cause a range of symptoms related to vision and balance, which can unfortunately negatively impact daily life and activities. Some of these include:^1,2

• Impaired or blurred vision: The constant eye movements can make it difficult to focus clearly on objects. This is one of the early symptoms of SN
• Vertigo: A feeling of dizziness or spinning is usually brought on when a lesion is present in the inner ear’s vestibular system, as it plays a key role in balance
• Oscillopsia: The illusion that an object or the environment is in movement, even though it is stationary
• Reduced balance and coordination: As with vertigo, this is a consequence of the inner ear being affected
• Abnormal head positioning: To compensate for and relieve balance or visual disturbance, an affected individual may try to tilt or turn their head

When left untreated, these symptoms can negatively impact the quality of life of those affected. They make it difficult, sometimes impossible, to perform daily activities such as reading, walking, or driving, significantly reducing overall quality of life.

Underlying causes of Spontaneous Nystagmus

Peripheral causes

SN can often be the result of disorders affecting the inner ear’s vestibular system. The vestibular system plays an essential role in balance and coordination through the vestibulo-ocular reflex (VOR), which is key to keeping your vision steady when turning your head.²

The following are examples of conditions that can result in peripheral SN:⁶

• Vestibular neuritis: The inflammation of the vestibular nerve in the inner ear can impair the VOR, resulting in SN with the most prominent symptoms being vertigo and balance issues
• Labyrinth injury: Damage to the labyrinth, or inner ear, can result from surgical procedures or head injury. Infection or inflammation of the labyrinth can cause nystagmus, accompanied by dizziness and hearing loss
• Ménière’s disease: This condition is associated with a buildup of fluid in the inner ear that disrupts the functioning of the vestibular system, and can trigger SN along with its associated symptoms

VOR is critical to the ability to stabilize vision by compensating for any movement of the head. When peripheral vestibular function is impaired, SN occurs as a compensatory mechanism.

Central causes

Central causes for NS include abnormalities in the brainstem or cerebellum, but it can also result from drug toxicity (including alcohol toxicity).¹

• Brainstem or cerebellar anomalies: Lesions in either of these two areas of the brain can be very disruptive to the VOR, leading to SN. The type of SN depends on the exact area that is affected⁷
• Drug toxicity: Some drugs, such as antiepileptics, but also alcohol, can impair central pathways in the brain, triggering SN^7,8

Congenital vs. acquired

As mentioned, SN can also be congenital or acquired when it is not physiological:

• Congenital causes: Some genetic mutations or developmental abnormalities affecting the control of eye movements or VOR can result in SN early in life. For example, a large proportion of people with albinism are affected by congenital SN⁹
• Acquired causes: SN can also result from central nervous disorders or trauma such as multiple sclerosis, head injury, brain tumor, metabolic disorders, medication side effects, or alcohol/drug toxicity¹

How is Spontaneous Nystagmus diagnosed?

Diagnosing SN requires a thorough assessment that includes a physical exam of the eyes and specialized testing to assess how well the vestibular system is functioning.

The health care provider usually starts by observing the patient's eye movements to identify spontaneous nystagmus, noting criteria such as direction, amplitude, and whether visual fixation suppresses the nystagmus.¹⁰ To further evaluate vestibular function, tests like videonystagmography (VNG) are employed; VNG is a test that uses infrared cameras to record the movements of the eyes in response to specific stimuli, helping to detect abnormalities in the vestibular system and VOR.¹¹

Additionally, the video head impulse test (vHIT) is another tool to assess the VOR by measuring eye movements during rapid head rotations. Imaging tests such as CT scan or MRI are important to check for the precise location of lesions in the inner ear or the brain.¹⁰

These tests and tools are integral in determining the underlying causes of SN and formulating appropriate treatment plans.

Treatment options

SN can be treated by addressing the underlying cause, including treating an infection of the vestibular nerve, managing vestibular disorders, or addressing a neurological issue.

A few medications have shown some efficacy in reducing the amplitude of the eye movements in SN, and therefore improving symptoms. Some of these drugs include gabapentin, baclofen and clonazepam.¹²

A doctor will carefully pick a medication that is best adapted for the individual patient, based on their own medical history and diagnosis. In some situations, the use of special prism lenses or contacts might be advised to temper the severity of the nystagmus. In rare instances, when medications and optical devices have been ineffective, surgery of the muscle around the eye can be recommended¹³.

Summary

Spontaneous nystagmus is a condition characterised by rapid and oscillatory movements of the eyes in the absence of any external trigger. The eye movements can happen in various directions (horizontal, vertical, or circular), and can be classified as jerk or pendular depending on the presence or lack of slow and fast phases. SN can be congenital or acquired later in life, and usually involves a dysfunction in the central (brainstem or cerebellum) or peripheral (inner ear) vestibular system. SN can cause a range of symptoms, including blurred vision, reduced balance and coordination, and vertigo, which often negatively impacts the ability to perform daily activities. Early detection by a healthcare professional and tailored treatment are important to improve quality of life. Therefore, one should promptly seek medical advice if experiencing symptoms such as uncontrolled eye movements or dizziness.