Nystagmus
Nystagmus is a fascinating yet often disruptive condition characterized by rhythmic, involuntary eye movements. It can profoundly affect vision and balance, making the world seem to constantly shift. Understanding this complex neurological phenomenon reveals much about how our visual and balance systems work—or sometimes, don't. Nystagmus is a rapid, involuntary eye movement that can significantly impair stable vision and spatial perception. It stems from disruptions in the intricate pathways linking our inner ear, brain, and eye muscles, affecting how we maintain gaze. While once considered untreatable, modern diagnostic tools and an array of therapies now offer hope for managing and mitigating its effects.
AI Summary
Nystagmus is a fascinating yet often disruptive condition characterized by rhythmic, involuntary eye movements. It can profoundly affect vision and balance, making the world seem to constantly shift. Understanding this complex neurological phenomenon reveals much about how our visual and balance systems work—or sometimes, don't.
- Nystagmus is a rapid, involuntary eye movement that can significantly impair stable vision and spatial perception.
- It stems from disruptions in the intricate pathways linking our inner ear, brain, and eye muscles, affecting how we maintain gaze.
- While once considered untreatable, modern diagnostic tools and an array of therapies now offer hope for managing and mitigating its effects.
What is Nystagmus?
Imagine your eyes constantly moving, even when you try to hold them still—that's nystagmus. It's an involuntary, repetitive oscillation of the eyes, which can sometimes be consciously induced, but more often is entirely beyond a person's control. This incessant movement often leads to reduced or limited vision.
To understand nystagmus, let's first consider how our eyes normally stay steady. As you turn your head, a remarkable system called the vestibulo-ocular reflex, or VOR, automatically rotates your eyes in the opposite direction. This keeps your gaze locked on a distant object, ensuring the world doesn't blur with every head turn.
This reflex relies on intricate signals. Your inner ear's semicircular canals sense angular head acceleration, sending signals to eye movement centers in your brain. These then command your extraocular muscles to keep your eyes perfectly aligned. Nystagmus occurs when these canals are unexpectedly stimulated, even if your head isn't moving, causing your eyes to drift and then 'snap back'.
Two Forms: Physiological and Pathological
Nystagmus presents in two primary forms: physiological and pathological. While the term 'involuntary eye movement' often sounds concerning, some types are perfectly normal and actually help our vision, while others signal an underlying issue that needs attention.
Physiological nystagmus is a natural, involuntary eye movement that occurs under specific, healthy conditions. For example, if you spin in a chair and then suddenly stop, your eyes will temporarily exhibit a rhythmic back-and-forth movement — that's postrotatory nystagmus, a normal response.
Pathological nystagmus, however, is a deviation from this healthy state. It arises when the delicate balance of the vestibular system—which includes the inner ear and parts of the brain that process balance and spatial orientation—is disrupted. This form usually degrades vision and can create the unsettling sensation of 'oscillopsia', where the world appears to constantly move.
The Many Causes
The causes of pathological nystagmus are incredibly diverse, ranging from conditions present at birth to those acquired later in life. It can be a standalone issue, a symptom of another neurological disorder, or even temporarily induced by substances or extreme disorientation.
Early-onset Nystagmus
Early-onset nystagmus is more common than acquired forms and typically appears in infancy. Though often mild and non-progressive, its impact on vision varies greatly. Interestingly, many individuals with early-onset nystagmus are unaware of their constant eye movements.
This congenital form can be isolated or accompany other conditions like micro-ophthalmic anomalies or Down syndrome. Specific causes often include visual pathway abnormalities, such as: Albinism Aniridia Congenital cataracts Optic nerve hypoplasia Leber's congenital amaurosis Rod monochromatism
Intriguingly, some early-onset nystagmus types are linked to specific gene mutations. For instance, X-linked infantile nystagmus is associated with mutations in the FRMD7 gene on the X chromosome. Other X-linked eye diseases, like congenital stationary night blindness (CSNB), also involve genes crucial for ion channel function, such as NYX and CACNA1F.
Acquired Nystagmus
Acquired nystagmus, appearing in childhood or adulthood, often has a more identifiable cause, though it can also be idiopathic—meaning its origin is unknown. Common culprits include central nervous system disorders, metabolic imbalances, or exposure to certain drugs and alcohol.
In older adults, a stroke is the most frequent cause of acquired nystagmus, highlighting its neurological roots. Other significant causes include severe thiamine deficiency, also known as beriberi, which can lead to neurological conditions like Wernicke encephalopathy and Korsakoff syndrome.
Central nervous system disorders are another major source. Problems in the cerebellum, the brain's coordination center, can produce nystagmus in almost any direction. Purely vertical nystagmus, for example, nearly always points to a CNS issue, though it's also a known side effect of high phenytoin toxicity.
How is Nystagmus Diagnosed?
Diagnosing nystagmus involves keen observation and specialized tests. While it's highly noticeable, it's often not immediately recognized as a distinct condition. Clinicians use several non-invasive methods to investigate these eye movements and pinpoint their cause.
One classic test is the caloric reflex test. Here, warm or cold water (or air) is gently irrigated into one ear canal. This temperature change stimulates the horizontal semicircular canal, artificially inducing a physiological nystagmus. Observing this induced response can provide crucial diagnostic clues about the vestibular system.
To precisely record and quantify eye movements, specialists use devices like an Electronystagmograph (ENG) or a Videonystagmograph (VNG). ENG uses external electrodes to measure electrical changes from eye movements, while VNG employs small cameras built into head masks for video-based tracking.
These objective recording techniques have revolutionized our understanding of nystagmus. They allow for much greater accuracy in measurement and help distinguish nystagmus from other eye movement disorders, like opsoclonus or ocular flutter, which might look similar but are fundamentally different.
Nystagmus is uniquely characterized by a combination of a slow, drifting 'pursuit' phase, taking the eye off target, interspersed with a rapid 'saccadic' phase that snaps it back. This two-phase movement is key to differentiating it from other conditions that involve only fast, saccadic eye movements.
Varieties of Movement
The direction of nystagmus is always defined by its quick phase. So, a 'right-beating nystagmus' means the quick, corrective movement is towards the right. These oscillations can occur in any plane—horizontal, vertical, or even torsional (rotational)—or any combination thereof.
Such movements are often given descriptive names, like 'downbeat nystagmus', 'upbeat nystagmus', or 'seesaw nystagmus'. However, these historical terms, based on subjective observation, don't always fully capture the eye's true, complex trajectory, emphasizing the need for objective measurement.
Beyond spontaneous pathological movements, nystagmus can also be evoked. Optokinetic nystagmus, for instance, is induced by watching a continuously moving visual pattern, like stripes on a rotating drum. Your eyes follow a stripe smoothly, then quickly jump back to catch the next—a fascinating insight into our fixation reflex.
Paths to Treatment
For a long time, congenital nystagmus was considered untreatable, a condition one simply had to live with. However, recent decades have brought significant advancements, with various therapeutic approaches now offering hope and improvement for many patients.
Pharmaceutical interventions have shown particular promise. Drugs like baclofen were found to stop periodic alternating nystagmus, and later, the anticonvulsant gabapentin brought improvement to about half of patients. Other medications such as memantine, levetiracetam, and 4-aminopyridine are also proving effective for certain types.
Surgical options are also available, particularly for congenital nystagmus. Procedures like tenotomy aim to weaken specific eye muscles to reduce the oscillations, which can remarkably improve visual acuity and help correct abnormal head postures adopted to minimize nystagmus.
Beyond medication and surgery, other supportive treatments include contact lenses, low vision rehabilitation strategies, and physical or occupational therapy. These approaches focus on helping individuals compensate for their impaired visual system and improve their quality of life.
While some alternative therapies, like acupuncture, have been explored, current evidence-based medicine suggests conflicting or insufficient data to support their widespread clinical use. More rigorous studies are needed to determine their true efficacy.
Beyond the Clinic
Nystagmus is more common than many realize, affecting approximately one in several thousand people. Historical descriptions of involuntary eye movements date back to antiquity, illustrating its long-standing presence in human experience.
In the United States, horizontal gaze nystagmus (HGN) is even incorporated into field sobriety tests. Police officers observe a suspect's eye movements as they follow an object, looking for signs like lack of smooth pursuit or distinct jerking at maximum deviation, which can indicate impairment from alcohol or central nervous system depressants.
While the HGN test has faced criticism regarding its methodology, peer-reviewed studies generally support its validity as an indicator of blood alcohol content, often proving more accurate than other standard field sobriety tests.
Living with nystagmus can be a unique challenge, as explored in documentaries like 'My Dancing Eyes'. Such media helps raise awareness and shares personal stories, offering insight into what it's truly like to navigate a world that never quite holds still.
Article
Nystagmus
Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. People can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision.
In normal eyesight, while the head rotates about an axis, distant visual images are sustained by rotating eyes in the opposite direction of the respective axis. The semicircular canals in the vestibule of the ear sense angular acceleration, and send signals to the nuclei for eye movement in the brain. From here, a signal is relayed to the extraocular muscles to allow one's gaze to fix on an object as the head moves. Nystagmus occurs when the semicircular canals are stimulated (e.g., by means of the caloric test, or by disease) while the head is stationary. The direction of ocular movement is related to the semicircular canal that is being stimulated.
There are two key forms of nystagmus: pathological and physiological, with variations within each type. Physiological nystagmus occurs under normal conditions in healthy subjects. Nystagmus may be caused by congenital disorder or sleep deprivation, acquired or central nervous system disorders, toxicity, pharmaceutical drugs, alcohol, or rotational movement. Previously considered untreatable, in recent years several drugs have been identified for treatment of nystagmus. Nystagmus is also occasionally associated with vertigo.
Causes
Nystagmus
Nystagmus as seen in a case of ocular albinism
The cause of pathological nystagmus may be congenital, idiopathic, or secondary to a pre-existing neurological disorder. It also may be induced temporarily by disorientation (such as on roller coaster rides or when a person has been spinning in circles) or by some drugs (alcohol, lidocaine, and other central nervous system depressants, inhalant drugs, stimulants, psychedelics, and dissociative drugs).
Early-onset nystagmus
Early-onset nystagmus occurs more frequently than acquired nystagmus. It can be insular or accompany other disorders (such as micro-ophthalmic anomalies or Down syndrome). Early-onset nystagmus itself is usually mild and non-progressive. The affected persons are usually unaware of their spontaneous eye movements, but vision can be impaired depending on the severity of the eye movements.
Types of early-onset nystagmus include the following, along with some of their causes:
• Infantile: • Albinism • Aniridia • Bilateral congenital cataract • Bilateral optic nerve hypoplasia • Idiopathic • Leber's congenital amaurosis • Optic nerve or macular disease • Persistent tunica vasculosa lentis • Rod monochromatism • Visual-motor syndrome of functional monophthalmus • Latent nystagmus • Noonan syndrome • Nystagmus blockage syndrome
X-linked infantile nystagmus is associated with mutations of the gene FRMD7, which is located on the X chromosome.
Infantile nystagmus is also associated with two X-linked eye diseases known as complete congenital stationary night blindness (CSNB) and incomplete CSNB (iCSNB or CSNB-2), which are caused by mutations of one of two genes located on the X chromosome. In CSNB, mutations are found in NYX (nyctalopin). CSNB-2 involves mutations of CACNA1F, a voltage-gated calcium channel that, when mutated, does not conduct ions.
Acquired nystagmus
Nystagmus that occurs later in childhood or in adulthood is called acquired nystagmus. The cause is often unknown, or idiopathic, and thus referred to as idiopathic nystagmus. Other common causes include diseases and disorders of the central nervous system, metabolic disorders and alcohol and drug toxicity. In the elderly, stroke is the most common cause.
General diseases and conditions
Some of the diseases that present nystagmus as a pathological sign or symptom are as follows:
Thiamine deficiency
Risk factors for thiamine deficiency, or beriberi, in turn include a diet of mostly white rice, as well as alcoholism, dialysis, chronic diarrhea, and taking high doses of diuretics. Rarely it may be due to a genetic condition that results in difficulties absorbing thiamine found in food. Wernicke encephalopathy and Korsakoff syndrome are forms of dry beriberi.
Central nervous system (CNS) diseases and disorders
Central nervous system disorders such as with a cerebellar problem, the nystagmus can be in any direction including horizontal. Purely vertical nystagmus usually originates in the central nervous system, but it is also an adverse effect commonly seen in high phenytoin toxicity. Other causes of toxicity that may result in nystagmus include:
Diagnosis
Nystagmus
Fast-phase horizontal eye movement vision
Fast-phase vertical eye movement vision
Nystagmus is highly noticeable but rarely recognized. Nystagmus can be clinically investigated by using a number of non-invasive standard tests. The simplest one is the caloric reflex test, in which one ear canal is irrigated with warm or cold water or air. The temperature gradient provokes the stimulation of the horizontal semicircular canal and the consequent nystagmus. Nystagmus is often very commonly present with Chiari malformation.
The resulting movement of the eyes may be recorded and quantified by a special device called an electronystagmograph (ENG), a form of electrooculography (an electrical method of measuring eye movements using external electrodes), or an even less invasive device called a videonystagmograph (VNG), a form of video-oculography (VOG) (a video-based method of measuring eye movements using external small cameras built into head masks), administered by an audiologist. Special swinging chairs with electrical controls can be used to induce rotatory nystagmus.
Over the past forty years, objective eye-movement-recording techniques have been applied to the study of nystagmus, and the results have led to greater accuracy of measurement and understanding of the condition.
Orthoptists may also use an optokinetic drum, or electrooculography or Frenzel goggles to assess a patient's eye movements.
Nystagmus can be caused by subsequent foveation of moving objects, pathology, sustained rotation or substance use. Nystagmus is not to be confused with other superficially similar-appearing disorders of eye movements (saccadic oscillations) such as opsoclonus or ocular flutter that are composed purely of fast-phase (saccadic) eye movements, while nystagmus is characterized by the combination of a smooth pursuit, which usually acts to take the eye off the point of focus, interspersed with the saccadic movement that serves to bring the eye back on target. Without the use of objective recording techniques, it may be very difficult to distinguish among these conditions.
In medicine, the presence of nystagmus can be benign, or it can indicate an underlying visual or neurological problem.
Pathological nystagmus
Pathological nystagmus is characterized by "excessive drifts of stationary retinal images that degrades vision and may produce illusory motion of the seen world: oscillopsia (an exception is congenital nystagmus)".
Bechterew's phenomenon was discovered by Vladimir Bekhterev in 1883 in animal experiments. Specifically, if one side of the vestibular system is damaged, then due to the lack of vestibular signal from that side, the animal behaves with nystagmus and vertigo. After a while, due to vestibular compensation, nystagmus and vertigo stops. However, if then the other vestibular system is damaged, then nystagmus and vertigo occurs in the opposite direction. This is an early evidence of sensorimotor adaptation in the brain. It is rarely reported in humans.
When nystagmus occurs without fulfilling its normal function, it is pathologic (deviating from the healthy or normal condition). Pathological nystagmus is the result of damage to one or more components of the vestibular system, including the semicircular canals, otolith organs, and the vestibulocerebellum.
Pathological nystagmus generally causes a degree of vision impairment, although the severity of such impairment varies widely. Also, many blind people have nystagmus, which is one reason that some wear dark glasses.
Variations
• Central nystagmus occurs as a result of either normal or abnormal processes not related to the vestibular organ. For example, lesions of the midbrain or cerebellum can result in up- and down-beat nystagmus. • Gaze induced nystagmus occurs or is exacerbated as a result of changing one's gaze toward or away from a particular side which has an affected central apparatus. • Peripheral nystagmus occurs as a result of either normal or diseased functional states of the vestibular system and may combine a rotational component with vertical or horizontal eye movements and may be spontaneous, positional, or evoked. • Positional nystagmus occurs when a person's head is in a specific position. An example of disease state in which this occurs is benign paroxysmal positional vertigo (BPPV). • Post rotational nystagmus occurs after an imbalance is created between a normal side and a diseased side by stimulation of the vestibular system by rapid shaking or rotation of the head. • Spontaneous nystagmus is nystagmus that occurs randomly, regardless of the position of the patient's head.
Physiological nystagmus
A diagram of the caloric reflex test, which tests the vestibulo-ocular reflex (VOR) by irrigating the ear canal with warm or cold water to induce physiological nystagmus. This image is showing effects of cold water introduced into right external meatus (Lawrence et al. 1960) - and these effects are opposite to that produced by introduction of hot water in same right ear.
Physiological nystagmus is a form of involuntary eye movement that is part of the vestibulo-ocular reflex (VOR), characterized by alternating smooth pursuit in one direction and saccadic movement in the other direction.
Variations
The direction of nystagmus is defined by the direction of its quick phase (e.g. a right-beating nystagmus is characterized by a rightward-moving quick phase, and a left-beating nystagmus by a leftward-moving quick phase). The oscillations may occur in the vertical, horizontal or torsional planes, or in any combination. The resulting nystagmus is often named as a gross description of the movement, e.g. downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus.
These descriptive names can be misleading, however, as many were assigned historically, solely on the basis of subjective clinical examination, which is not sufficient to determine the eyes' true trajectory.
• Optokinetic (syn. opticokinetic) nystagmus: a nystagmus induced by looking at moving visual stimuli, such as moving horizontal or vertical lines, and/or stripes. For example, if one fixates on a stripe of a rotating drum with alternating black and white, the gaze retreats to fixate on a new stripe as the drum moves. This is first a rotation with the same angular velocity, then returns in a saccade in the opposite direction. The process proceeds indefinitely. This is optokinetic nystagmus, and is a source for understanding the fixation reflex. • Postrotatory nystagmus: if one spins in a chair continuously and stops suddenly, the fast phase of nystagmus is in the opposite direction of rotation, known as the "post-rotatory nystagmus", while slow phase is in the direction of rotation.
Treatment
Nystagmus
Congenital nystagmus has long been viewed as untreatable, but medications have been discovered that show promise in some patients. In 1980, researchers discovered that a drug called baclofen could stop periodic alternating nystagmus. Subsequently, gabapentin, an anticonvulsant, led to improvement in about half the patients who took it. Other drugs found to be effective against nystagmus in some patients include memantine, levetiracetam, 3,4-diaminopyridine (available in the US to eligible patients with downbeat nystagmus at no cost under an expanded access program), 4-aminopyridine, and acetazolamide. Several therapeutic approaches, such as contact lenses, drugs, surgery, and low vision rehabilitation have also been proposed. For example, it has been proposed that mini-telescopic eyeglasses suppress nystagmus.
Surgical treatment of congenital nystagmus is aimed at improving head posture, simulating artificial divergence, or weakening the horizontal recti muscles. Clinical trials of a surgery to treat nystagmus (known as tenotomy) concluded in 2001. Tenotomy is now being performed regularly at numerous centres around the world. The surgery aims to reduce the eye oscillations, which in turn tends to improve visual acuity.
Acupuncture tests have produced conflicting evidence on its beneficial effects on the symptoms of nystagmus. Benefits have been seen in treatments in which acupuncture points of the neck were used, specifically points on the sternocleidomastoid muscle. Benefits of acupuncture for treatment of nystagmus include a reduction in frequency and decreased slow phase velocities, which led to an increase in foveation duration periods both during and after treatment. By the standards of evidence-based medicine, the quality of these studies is poor (for example, Ishikawa's study had sample size of six subjects, was unblinded, and lacked proper controls), and given high quality studies showing that acupuncture has no effect beyond placebo, the results of these studies have to be considered clinically irrelevant until higher quality studies are performed.
Physical or occupational therapy is also used to treat nystagmus. Treatment consists of learning strategies to compensate for the impaired system.
A Cochrane Review on interventions for eye movement disorders due to acquired brain injury, updated in June 2017, identified three studies of pharmacological interventions for acquired nystagmus but concluded that these studies provided insufficient evidence to guide treatment choices.
Epidemiology
Nystagmus
Nystagmus is a relatively common clinical condition, affecting one in several thousand people. First descriptions date back to antiquity. A survey conducted in Oxfordshire, United Kingdom, found that by the age of two, one in every 670 children had manifested nystagmus. Authors of another study in the United Kingdom estimated an incidence of 24 in 10,000 (c. 0.240%), noting an apparently higher rate amongst white Europeans than in individuals of Asian origin.
Law enforcement
Nystagmus
In the United States, testing for horizontal gaze nystagmus is one of a battery of field sobriety tests used by police officers to determine whether a suspect is driving under the influence of alcohol. Horizontal gaze nystagmus will show if a subject is under the influence of a central nervous system depressant, an inhalant, or a dissociative anesthetic. The test involves observation of the suspect's pupil as it follows a moving object, noting
• lack of smooth pursuit, • distinct and sustained nystagmus at maximum deviation, and • the onset of nystagmus prior to 45 degrees.
The horizontal gaze nystagmus test has been highly criticized and major errors in the testing methodology and analysis found. However, the validity of the horizontal gaze nystagmus test for use as a field sobriety test for persons with a blood alcohol level between 0.04 and 0.08 is supported by peer-reviewed studies and has been found to be a more accurate indication of blood alcohol content than other standard field sobriety tests.
Media
Nystagmus
My Dancing Eyes, a documentary by filmmaker Matt Morris, had participants explain what it is like to live with the eye condition, and was released for free. It was featured on NBN News, and ABC Radio Newcastle, in Australia.