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Nystagmus

Nystagmus is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nystagmus rather than just read about it. In short: 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.

Nystagmus — main illustration
Nystagmus — illustration

Key takeaways

  • Nystagmus belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Nystagmus to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Nystagmus from memory before moving on to harder problems.

Reference excerpt

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

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:

Aniridia Benign paroxysmal positional vertigo

Toxicity or intoxication, metabolic disorders and combination Sources of toxicity that could lead to nystagmus:

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:

Other causes Non-physiological Trochlear nerve malfunction Vestibular pathology (Ménière's disease, SCDS (superior canal dehiscence syndrome), BPPV, vestibular neuritis) Exposure to strong magnetic fields (as in MRI machines) Long-term exposure to low light conditions or darkness, called miner's nystagmus after 19th-century coal miners who developed nystagmus from working in the dark. A slightly different form of nystagmus may be produced voluntarily by some (8% of) people. Some can sustain it for up to 35 seconds, but most average around 5 seconds.

Diagnosis

… excerpt ends here. Continue reading the full article.

Illustrations

Nystagmus illustration
Nystagmus: Nystagmus as seen in a case of ocular albinism
Nystagmus as seen in a case of ocular albinism
Nystagmus: Fast-phase horizontal eye movement vision
Fast-phase horizontal eye movement vision
Nystagmus: Fast-phase vertical eye movement vision
Fast-phase vertical eye movement vision
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.
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.

Worked examples

Example 1 — a first encounter with Nystagmus

Start with the simplest possible case. Write down what Nystagmus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nystagmus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nystagmus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nystagmus

In research
Nystagmus appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Nystagmus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Nystagmus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Eye, Eye diseases, Medical signs, so understanding it makes those chapters shorter.
In everyday life
Look for Nystagmus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Nystagmus in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Nystagmus means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Nystagmus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nystagmus in simple terms?

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.

Why does Nystagmus matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nystagmus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nystagmus.

Tags

  • Eye
  • Eye diseases
  • Medical signs
  • Neurological disorders

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