|Horizontal optokinetic nystagmus, a normal (physiological) form of nystagmus|
Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement, acquired in infancy or later in life, that may result in reduced or limited vision. Due to the involuntary movement of the eye, it has been called "dancing eyes".[a]
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. 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.
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 by some drugs (alcohol, lidocaine, and other central nervous system depressants, inhalant drugs, stimulants, psychedelics, and dissociative drugs).
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:
- Latent nystagmus
- Noonan syndrome
- Nystagmus blockage syndrome
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.
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:
- Brain tumors (medulloblastoma, astrocytoma, or other tumors in the posterior fossa.)
- Canavan disease
- Head trauma
- Lateral medullary syndrome
- Ménière's disease and other balance disorders
- Multiple sclerosis
- Optic nerve hypoplasia
- Pelizaeus–Merzbacher disease
- Superior canal dehiscence syndrome
- Tullio phenomenon
- Whipple's disease
Toxicity or intoxication, metabolic disorders and combination
Sources of toxicity that could lead to nystagmus:
- Alcohol intoxication
- Phencyclidine (PCP)
- Phenytoin (Dilantin)
- Selective serotonin reuptake inhibitors (SSRIs)
- Other anticonvulsants or sedatives
- Thiamine deficiency
Risk factors for thiamine deficiency, or beri beri, 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:
- Trochlear nerve malfunction
- Vestibular Pathology (Ménière's disease, SCDS (superior canal dehiscence syndrome), BPPV, Labyrinthitis)
- Exposure to strong magnetic fields (as in MRI machines)
- A slightly different form of nystagmus may be produced voluntarily by some people.
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 devices 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.
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.
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)".
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.[contradictory]
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.
- 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 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.
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.
Congenital nystagmus has long been viewed as untreatable, but medications have been discovered in recent years that show promise in some patients. In 1980, researchers discovered that a drug called baclofen could stop periodic alternating nystagmus. Subsequently, gabapentin, an anticonvulsant, was 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.
Nystagmus is a relatively common clinical condition, affecting one in several thousand people. 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.
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. 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 0.04–0.08 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.
- Note however that "dancing eyes" is also a common term for opsoclonus myoclonus syndrome.
- Zahn JR (July 1978). "Incidence and characteristics of voluntary nystagmus". Journal of Neurology, Neurosurgery, and Psychiatry. 41 (7): 617–23. doi:10.1136/jnnp.41.7.617. PMC 493105. PMID 690639.
- "General Information about Nystagmus". American Nystagmus Network. February 21, 2002. Retrieved 2011-11-09.
- Weil A (2013). "Dealing with dancing eyes". Weil Lifestyle, LLC. Retrieved 2014-04-16.
- "Nystagmus". Medline Plus. February 27, 2013. Retrieved 2012-12-12.
- Saladin K (2012). Anatomy and Physiology: The Unity of Form and Function. New York: McGraw-Hill. pp. 597–609. ISBN 978-0-07-337825-1.
- Self J, Lotery A (December 2007). "A review of the molecular genetics of congenital Idiopathic Nystagmus (CIN)". Ophthalmic Genetics. 28 (4): 187–91. doi:10.1080/13816810701651233. PMID 18161616.
- Li N, Wang L, Cui L, Zhang L, Dai S, Li H, et al. (April 2008). "Five novel mutations of the FRMD7 gene in Chinese families with X-linked infantile nystagmus". Molecular Vision. 14: 733–8. PMC 2324116. PMID 18431453.
- Poopalasundaram S, Erskine L, Cheetham ME, Hardcastle AJ (December 2005). "Focus on molecules: nyctalopin". Experimental Eye Research. 81 (6): 627–8. doi:10.1016/j.exer.2005.07.017. PMID 16157331.
- Leroy BP, Budde BS, Wittmer M, De Baere E, Berger W, Zeitz C (May 2009). "A common NYX mutation in Flemish patients with X linked CSNB". The British Journal of Ophthalmology. 93 (5): 692–6. doi:10.1136/bjo.2008.143727. PMID 18617546.
- Peloquin JB, Rehak R, Doering CJ, McRory JE (December 2007). "Functional analysis of congenital stationary night blindness type-2 CACNA1F mutations F742C, G1007R, and R1049W". Neuroscience. 150 (2): 335–45. doi:10.1016/j.neuroscience.2007.09.021. PMID 17949918.
- Dorigueto RS, Ganança MM, Ganança FF (2005). "The number of procedures required to eliminate positioning nystagmus in benign paroxysmal positional vertigo" [The number of procedures required to eliminate positioning nystagmus in benign paroxysmal positional vertigo]. Brazilian Journal of Otorhinolaryngology (in Portuguese). 71 (6): 769–75. doi:10.1590/S0034-72992005000600013. PMID 16878247.
- "Beriberi". Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. 2015. Archived from the original on 11 November 2017. Retrieved 11 November 2017.
- "Nutrition and Growth Guidelines | Domestic Guidelines - Immigrant and Refugee Health". CDC. March 2012. Archived from the original on 11 November 2017. Retrieved 11 November 2017.
- Lindgren S (1993). Kliniska färdigheter: Informationsutbytet mellan patient och läkare (in Swedish). Lund: Studentlitteratur. ISBN 978-91-44-37271-6.[page needed]
- Roberts DC, Marcelli V, Gillen JS, Carey JP, Della Santina CC, Zee DS (October 2011). "MRI magnetic field stimulates rotational sensors of the brain". Current Biology. 21 (19): 1635–40. doi:10.1016/j.cub.2011.08.029. PMC 3379966. PMID 21945276.
- Tusa RJ (June 1999). "Nystagmus: diagnostic and therapeutic strategies". Seminars in Ophthalmology. 14 (2): 65–73. doi:10.3109/08820539909056066. PMID 10758214.
- Markley BA (September 2007). "Introduction to electronystagmography for END technologists". American Journal of Electroneurodiagnostic Technology. 47 (3): 178–89. doi:10.1080/1086508X.2007.11079629. PMID 17982846.
- Mosca F, Sicignano S, Leone CA (April 2003). "Benign positional paroxysmal vertigo: videonystagmographic study using rotatory test". Acta Otorhinolaryngologica Italica. 23 (2): 67–72. PMID 14526552.
- Eggert T (2007). "Eye movement recordings: methods". Developments in Ophthalmology. 40: 15–34. doi:10.1159/000100347. ISBN 978-3-8055-8251-3. PMID 17314477.
- Serra A, Leigh RJ (December 2002). "Diagnostic value of nystagmus: spontaneous and induced ocular oscillations". Journal of Neurology, Neurosurgery, and Psychiatry. 73 (6): 615–8. doi:10.1136/jnnp.73.6.615. PMC 1757336. PMID 12438459.
- "Differences Between Physiologic and Pathologic Nystagmus". Spencer S. Eccles Health Sciences Library. Retrieved 22 November 2016.
- "nystagmus". Retrieved 2007-06-07.
- Gold D. "Gaze-evoked and rebound nystagmus in a cerebellar syndrome". Neuro-Ophthalmology Virtual Education Library (NOVEL): Daniel Gold Collection. Spencer S. Eccles Health Sciences Library. Retrieved 9 September 2019.
- Anagnostou E, Mandellos D, Limbitaki G, Papadimitriou A, Anastasopoulos D (June 2006). "Positional nystagmus and vertigo due to a solitary brachium conjunctivum plaque". Journal of Neurology, Neurosurgery, and Psychiatry. 77 (6): 790–2. doi:10.1136/jnnp.2005.084624. PMC 2077463. PMID 16705203.
- Pierrot-Deseilligny C, Milea D (June 2005). "Vertical nystagmus: clinical facts and hypotheses". Brain. 128 (Pt 6): 1237–46. doi:10.1093/brain/awh532. PMID 15872015.
- "Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 179 Encyclopædia Britannica, 1987
- Corbett J (September 2007). "Memantine/Gabapentin for the treatment of congenital nystagmus". Current Neurology and Neuroscience Reports. 7 (5): 395–6. doi:10.1007/s11910-007-0061-z. PMID 17764629.
- Muscular Dystrophy Association Press Release
- Clinical trial number NCT02189720 for "Expanded Access Study of Amifampridine Phosphate in LEMS, Congenital Myasthenic Syndrome, or Downbeat Nystagmus Patients (EAP-001)" at ClinicalTrials.gov
- Groves N (March 15, 2006). "Many options to treat nystagmus, more in development". Ophthalmology Times.
- Biousse V, Tusa RJ, Russell B, Azran MS, Das V, Schubert MS, et al. (February 2004). "The use of contact lenses to treat visually symptomatic congenital nystagmus". Journal of Neurology, Neurosurgery, and Psychiatry. 75 (2): 314–6. doi:10.1136/jnnp.2003.010678. PMC 1738913. PMID 14742616.
- Cerman E. "Mini-telescopic eyeglasses suppress nystagmus". World Society of Pediatric Ophthalmology and Strabismus Conference in Barcelona 2015. Retrieved 26 January 2016.
- Kumar A, Shetty S, Vijayalakshmi P, Hertle RW (Nov–Dec 2011). "Improvement in visual acuity following surgery for correction of head posture in infantile nystagmus syndrome". Journal of Pediatric Ophthalmology and Strabismus. 48 (6): 341–6. doi:10.3928/01913913-20110118-02. PMID 21261243.
- Wang Z, Dell'Osso LF, Jacobs JB, Burnstine RA, Tomsak RL (December 2006). "Effects of tenotomy on patients with infantile nystagmus syndrome: foveation improvement over a broadened visual field". Journal of AAPOS. 10 (6): 552–60. doi:10.1016/j.jaapos.2006.08.021. PMID 17189150.
- Ishikawa S, et al. (1987). "Treatment of nystagmus by acupuncture". Highlights in Neuro-ophthalmology (6th ed.): 227–232.
- Blekher T, Yamada T, Yee RD, Abel LA (February 1998). "Effects of acupuncture on foveation characteristics in congenital nystagmus". The British Journal of Ophthalmology. 82 (2): 115–20. doi:10.1136/bjo.82.2.115. PMC 1722486. PMID 9613375.
- Rowe FJ, Hanna K, Evans JR, Noonan CP, Garcia-Finana M, Dodridge CS, et al. (Cochrane Eyes and Vision Group) (March 2018). "Interventions for eye movement disorders due to acquired brain injury". The Cochrane Database of Systematic Reviews. 3: CD011290. doi:10.1002/14651858.CD011290.pub2. PMC 6494416. PMID 29505103.
- Sarvananthan N, Surendran M, Roberts EO, Jain S, Thomas S, Shah N, et al. (November 2009). "The prevalence of nystagmus: the Leicestershire nystagmus survey". Investigative Ophthalmology & Visual Science. 50 (11): 5201–6. doi:10.1167/iovs.09-3486. PMID 19458336.
- Booker JL (2004). "The Horizontal Gaze Nystagmus test: fraudulent science in the American courts". Science & Justice. 44 (3): 133–9. doi:10.1016/S1355-0306(04)71705-0. PMID 15270451.
- Booker JL (2001). "End-position nystagmus as an indicator of ethanol intoxication". Science & Justice. 41 (2): 113–6. doi:10.1016/S1355-0306(01)71862-X. PMID 11393940.
- McKnight AJ, Langston EA, McKnight AS, Lange JE (May 2002). "Sobriety tests for low blood alcohol concentrations". Accident Analysis and Prevention. 34 (3): 305–11. doi:10.1016/S0001-4575(01)00027-6. PMID 11939359.