Medicine:Nystagmus

From HandWiki
Short description: Dysfunction of eye movement
Nystagmus
Other namesDancing eyes, Instabilitas oculorum
Optokinetic nystagmus.gif
Horizontal optokinetic nystagmus, a normal (physiological) form of nystagmus
SpecialtyNeurology, ophthalmology, optometry

Nystagmus is a condition of involuntary (or voluntary, in some cases)[1] eye movement.[2] 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.[3]

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.[4] 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.[5]

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.

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

Example of congenital (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:

X-linked infantile nystagmus is associated with mutations of the gene FRMD7, which is located on the X chromosome.[6][7]

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).[8][9] CSNB-2 involves mutations of CACNA1F, a voltage-gated calcium channel that, when mutated, does not conduct ions.[10]

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:


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.[13][14] Rarely it may be due to a genetic condition that results in difficulties absorbing thiamine found in food.[13] Wernicke encephalopathy and Korsakoff syndrome are forms of dry beriberi.[14]

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[15]
  • Vestibular pathology (Ménière's disease, SCDS (superior canal dehiscence syndrome), BPPV, vestibular neuritis)
  • Exposure to strong magnetic fields (as in MRI machines)[16]
  • 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.[17]
  • A slightly different form of nystagmus may be produced voluntarily by some people.[18]

Diagnosis

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),[19] or an even less invasive device called a videonystagmograph (VNG),[20] 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.[21]

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.[22]

Pathologic 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)".[23]

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.[24][better source needed]

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.[25]
  • 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.[26] 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.

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,[27] 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.[28]
  • 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.[29]

Treatment

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,[30] levetiracetam, 3,4-diaminopyridine (available in the US to eligible patients with downbeat nystagmus at no cost under an expanded access program[31][32]), 4-aminopyridine, and acetazolamide.[33] Several therapeutic approaches, such as contact lenses,[34] drugs, surgery, and low vision rehabilitation have also been proposed. For example, it has been proposed that mini-telescopic eyeglasses suppress nystagmus.[35]

Surgical treatment of congenital nystagmus is aimed at improving head posture, simulating artificial divergence, or weakening the horizontal recti muscles.[36] 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.[37]

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.[38][39] 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.[39] 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,[citation needed] 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.[citation needed]

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.[40]

Epidemiology

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.[3] 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.[41]

Law enforcement

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

  1. lack of smooth pursuit,
  2. distinct and sustained nystagmus at maximum deviation, and
  3. 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.[42][43] 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[clarification needed] 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.[44]

Media

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.

See also

References

  1. ↑ "Incidence and characteristics of voluntary nystagmus". Journal of Neurology, Neurosurgery & Psychiatry 41 (7): 617–23. July 1978. doi:10.1136/jnnp.41.7.617. PMID 690639. 
  2. ↑ Weil, Andrew (2013). "Dealing with dancing eyes". Weil Lifestyle, LLC. http://www.drweil.com/drw/u/QAA401094/Dealing-With-Dancing-Eyes.html. 
  3. ↑ 3.0 3.1 "General Information about Nystagmus". American Nystagmus Network. February 21, 2002. http://www.nystagmus.org/aboutn.html. 
  4. ↑ MedlinePlus Encyclopedia Nystagmus
  5. ↑ Saladin, Kenneth (2012). Anatomy and Physiology: The Unity of Form and Function. New York: McGraw-Hill. pp. 597–609. ISBN 978-0-07-337825-1. 
  6. ↑ "A review of the molecular genetics of congenital Idiopathic Nystagmus (CIN)". Ophthalmic Genetics 28 (4): 187–91. December 2007. doi:10.1080/13816810701651233. PMID 18161616. 
  7. ↑ "Five novel mutations of the FRMD7 gene in Chinese families with X-linked infantile nystagmus". Molecular Vision 14: 733–8. April 2008. PMID 18431453. 
  8. ↑ "Focus on molecules: nyctalopin". Experimental Eye Research 81 (6): 627–8. December 2005. doi:10.1016/j.exer.2005.07.017. PMID 16157331. 
  9. ↑ "A common NYX mutation in Flemish patients with X linked CSNB". The British Journal of Ophthalmology 93 (5): 692–6. May 2009. doi:10.1136/bjo.2008.143727. PMID 18617546. https://biblio.ugent.be/publication/940940. 
  10. ↑ "Functional analysis of congenital stationary night blindness type-2 CACNA1F mutations F742C, G1007R, and R1049W". Neuroscience 150 (2): 335–45. December 2007. doi:10.1016/j.neuroscience.2007.09.021. PMID 17949918. 
  11. ↑ Ricardo, Schaffeln Dorigueto; Maurício, Malavasi Ganança; Fernando, Freitas Ganança (November 2005). "The number of procedures required to eliminate positioning nystagmus in benign paroxysmal positional vertigo". Brazilian Journal of Otorhinolaryngology 71 (6): 769–775. doi:10.1016/s1808-8694(15)31247-7. PMID 16878247. 
  12. ↑ García-Romo, E.; Blanco, R.; Nicholls, C.; Hernández-Tejero, A.; Fernández-de-Arévalo, B. (April 2021). "COVID-19 asociada a nistagmo". Archivos de la Sociedad Española de Oftalmología 96 (4): 224–226. doi:10.1016/j.oftal.2020.09.008. PMID 33279355. 
  13. ↑ 13.0 13.1 "Beriberi" (in en). 2015. https://rarediseases.info.nih.gov/diseases/9948/beriberi. 
  14. ↑ 14.0 14.1 "Nutrition and Growth Guidelines | Domestic Guidelines - Immigrant and Refugee Health" (in en-us). March 2012. https://www.cdc.gov/immigrantrefugeehealth/guidelines/domestic/nutrition-growth.html. 
  15. ↑ Lindgren, Stefan (1993) (in sv). Kliniska färdigheter: Informationsutbytet mellan patient och läkare. Lund: Studentlitteratur. ISBN 978-91-44-37271-6. [page needed]
  16. ↑ "MRI magnetic field stimulates rotational sensors of the brain". Current Biology 21 (19): 1635–40. October 2011. doi:10.1016/j.cub.2011.08.029. PMID 21945276. 
  17. ↑ Millodot, Michel (2014-07-30) (in en). Dictionary of Optometry and Visual Science E-Book. Elsevier Health Sciences. pp. 250. ISBN 978-0-7020-5188-3. https://books.google.com/books?id=3gygBAAAQBAJ&pg=PA250. 
  18. ↑ "Nystagmus: diagnostic and therapeutic strategies". Seminars in Ophthalmology 14 (2): 65–73. June 1999. doi:10.3109/08820539909056066. PMID 10758214. 
  19. ↑ "Introduction to electronystagmography for END technologists". American Journal of Electroneurodiagnostic Technology 47 (3): 178–89. September 2007. doi:10.1080/1086508X.2007.11079629. PMID 17982846. 
  20. ↑ "Benign positional paroxysmal vertigo: videonystagmographic study using rotatory test". Acta Otorhinolaryngologica Italica 23 (2): 67–72. April 2003. PMID 14526552. 
  21. ↑ Eggert, Thomas (2007). "Eye Movement Recordings: Methods". Neuro-Ophthalmology. Developments in Ophthalmology. 40. pp. 15–34. doi:10.1159/000100347. ISBN 978-3-8055-8251-3. 
  22. ↑ "Diagnostic value of nystagmus: spontaneous and induced ocular oscillations". Journal of Neurology, Neurosurgery, and Psychiatry 73 (6): 615–8. December 2002. doi:10.1136/jnnp.73.6.615. PMID 12438459. 
  23. ↑ "Differences Between Physiologic and Pathologic Nystagmus". Spencer S. Eccles Health Sciences Library. http://content.lib.utah.edu/cdm/ref/collection/EHSL-NOVEL/id/1855. 
  24. ↑ "nystagmus". http://www.drhull.com/EncyMaster/N/nystagmus.html. 
  25. ↑ Gold, Daniel. "Gaze-evoked and rebound nystagmus in a cerebellar syndrome". Spencer S. Eccles Health Sciences Library. https://collections.lib.utah.edu/ark:/87278/s6089dz6. 
  26. ↑ "Positional nystagmus and vertigo due to a solitary brachium conjunctivum plaque". Journal of Neurology, Neurosurgery, and Psychiatry 77 (6): 790–2. June 2006. doi:10.1136/jnnp.2005.084624. PMID 16705203. 
  27. ↑ Pierrot-Deseilligny, C.; Milea, D. (1 June 2005). "Vertical nystagmus: clinical facts and hypotheses". Brain 128 (6): 1237–1246. doi:10.1093/brain/awh532. PMID 15872015. 
  28. ↑ "Testing for Optokinetic Nystigmus". pp. 109–111. https://books.google.com/books?id=pEQhV88LTJYC&pg=PA109.  in Laroche, G. Robert (2011). "Examining the Visual System". in Goldbloom, Richard B.. Pediatric Clinical Skills. pp. 101–121. doi:10.1016/B978-1-4377-1397-8.00008-3. ISBN 978-1-4377-1397-8. 
  29. ↑ Simón, V.; Bartual, J.; Llopis, M. (1975). "Physiological Postrotatory Nystagmus". Stereotactic and Functional Neurosurgery 38 (3): 161–171. doi:10.1159/000102658. PMID 1232915. 
  30. ↑ "Memantine/Gabapentin for the treatment of congenital nystagmus". Current Neurology and Neuroscience Reports 7 (5): 395–6. September 2007. doi:10.1007/s11910-007-0061-z. PMID 17764629. 
  31. ↑ Muscular Dystrophy Association Press Release
  32. ↑ 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
  33. ↑ Groves, Nancy (March 15, 2006). "Many options to treat nystagmus, more in development". Ophthalmology Times. http://www.ophthalmologytimes.com/ophthalmologytimes/article/articleDetail.jsp?id=313686. 
  34. ↑ "The use of contact lenses to treat visually symptomatic congenital nystagmus". Journal of Neurology, Neurosurgery, and Psychiatry 75 (2): 314–6. February 2004. doi:10.1136/jnnp.2003.010678. PMID 14742616. 
  35. ↑ "Mini-telescopic eyeglasses suppress nystagmus". http://wspos.org/barcelona-2015/barcelona-2015-video-abstracts?sessiom=48. 
  36. ↑ "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. Nov–Dec 2011. doi:10.3928/01913913-20110118-02. PMID 21261243. 
  37. ↑ "Effects of tenotomy on patients with infantile nystagmus syndrome: foveation improvement over a broadened visual field". Journal of AAPOS 10 (6): 552–60. December 2006. doi:10.1016/j.jaapos.2006.08.021. PMID 17189150. 
  38. ↑ Ishikawa, S.; Ozawa, H.; Fujiyama, Y. (1987). "Treatment of nystagmus by acupuncture". in Ishikawa, Satoshi. Highlights in Neuro-ophthalmology: Proceedings of the Sixth Meeting of the International Neuro-ophthalmology Society (INOS), Hakone, Japan, 8-14 June, 1986. Aeolus Press. pp. 227–232. ISBN 978-90-70430-03-0. 
  39. ↑ 39.0 39.1 "Effects of acupuncture on foveation characteristics in congenital nystagmus". The British Journal of Ophthalmology 82 (2): 115–20. February 1998. doi:10.1136/bjo.82.2.115. PMID 9613375. 
  40. ↑ "Interventions for eye movement disorders due to acquired brain injury". The Cochrane Database of Systematic Reviews 2018 (3): CD011290. March 2018. doi:10.1002/14651858.CD011290.pub2. PMID 29505103. 
  41. ↑ "The prevalence of nystagmus: the Leicestershire nystagmus survey". Investigative Ophthalmology & Visual Science 50 (11): 5201–6. November 2009. doi:10.1167/iovs.09-3486. PMID 19458336. 
  42. ↑ "The Horizontal Gaze Nystagmus test: fraudulent science in the American courts". Science & Justice 44 (3): 133–9. 2004. doi:10.1016/S1355-0306(04)71705-0. PMID 15270451. 
  43. ↑ "End-position nystagmus as an indicator of ethanol intoxication". Science & Justice 41 (2): 113–6. 2001. doi:10.1016/S1355-0306(01)71862-X. PMID 11393940. 
  44. ↑ "Sobriety tests for low blood alcohol concentrations". Accident Analysis and Prevention 34 (3): 305–11. May 2002. doi:10.1016/S0001-4575(01)00027-6. PMID 11939359. 
Classification
External resources



Retrieved from "https://handwiki.org/wiki/index.php?title=Medicine:Nystagmus&oldid=3271646"