Nystagmus

Nystagmus

Horizontal optokinetic nystagmus, a normal (physiological) form of nystagmus
Classification and external resources
Specialty Otorhinolaryngology
ICD-10 H55, H81.4
ICD-9-CM 379.50, 794.14
DiseasesDB 23470
MedlinePlus 003037
eMedicine article/1199177
Patient UK Nystagmus
MeSH D009759

Nystagmus /nɪˈstæɡməs/ is a condition of involuntary (or voluntary, in rare cases)[1] eye movement, acquired in infancy or later in life, that may result in reduced or limited vision.[2] Due to the involuntary movement of the eye, it is often called "dancing eyes".[3][lower-alpha 1]

In a normal condition, while the head rotates about any axis, distant visual images are sustained by rotating eyes in the opposite direction on the respective axis.[4] The semicircular canals in the vestibule sense angular acceleration. These 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 fixate on one object as the head moves. Nystagmus occurs when the semicircular canals are being stimulated while the head is not in motion. 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 disorders, acquired or central nervous system disorders, toxicity, pharmaceutical drugs, alcohol, or rotational movement. Previously considered untreatable, in recent years several pharmaceutical drugs have been identified for treatment of nystagmus. Nystagmus is occasionally associated with vertigo.

Diagnosis

Nystagmus is very 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 special devices called electronystagmograph (ENG), a form of electrooculography (an electrical method of measuring eye movements using external electrodes),[6] or even less invasive devices called videonystagmograph (VNG),[7] a form of video-oculography (VOG) (a video-based method of measuring eye movements using external small cameras built into head masks) by an audiologist. Special swinging chairs with electrical controls can be used to induce rotatory nystagmus.[8]

Over the past forty years, objective eye-movement-recording techniques have been applied to the study of nystagmus, and the results have led to a greater accuracy and understanding of the condition.

Orthoptists may also use an optokinetic drum, or electrooculography 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 characterised by the combination of a smooth pursuit, which usually acts to take the eye off the point of regard, 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 between these conditions.

In medicine, the presence of nystagmus can be benign, or it can indicate an underlying visual or neurological problem.[9]

Pathologic nystagmus

Pathologic nystagmus is characterized by a biphasic ocular oscillation alternating a slow eye movement, or smooth pursuit, in one direction and a fast eye movement, or saccadic movement, in the other direction. The velocity of the slow phase eye velocity (SPEV) and the fast phase eye velocity (FPEV) are related to each other and can be considered as a measurement of the efficiency of the system stimulus/response.[10]

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.[11]

Variations

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,[13] 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.

Causes

The cause for 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 certain drugs (alcohol and other central nervous system depressants, inhalant drugs, stimulants, psychedelic drugs, 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 not normally aware of their spontaneous eye movements, but vision can be impaired depending on the severity of the movements.

Types of early-onset nystagmus include the following:

X-linked infantile nystagmus is associated with mutations of the gene FRMD7, which is located on the X chromosome.[15][16]

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).[17][18] CSNB-2 involves mutations of CACNA1F, a voltage-gated calcium channel that, when mutated, does not conduct ions.[19]

Acquired nystagmus

It may be acquired from:

Other causes

Alcohol

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

  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.[22][23] 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.[24]

Treatment

Congenital nystagmus has traditionally been viewed as non-treatable, but medications have been discovered in recent years that show promise in some patients. In 1980, researchers discovered that a drug called baclofen could effectively stop periodic alternating nystagmus. Subsequently, gabapentin, an anticonvulsant, was found to cause improvement in about half the patients who received it to relieve symptoms of nystagmus. Other drugs found to be effective against nystagmus in some patients include memantine,[25] levetiracetam, 3,4-diaminopyridine (available in the US to eligible patients with downbeat nystagmus at no cost under an expanded access program[26][27]), 4-aminopyridine, and acetazolamide.[28] Several therapeutic approaches, such as contact lenses,[29] drugs, surgery, and low vision rehabilitation have also been proposed. For example it has been proposed that mini-telescopic eyeglasses suppress nystagmus.[30]

Surgical treatment of Congenital Nystagmus is aimed at improving the abnormal head posture, simulating artificial divergence or weakening the horizontal recti muscles.[31] 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 developed by Louis F. Dell'Osso Ph.D. aims to reduce the eye shaking (oscillations), which in turn tends to improve visual acuity.[32]

Acupuncture has conflicting evidence as to having beneficial effects on the symptoms of nystagmus. Benefits have been seen in treatments where acupuncture points of the neck were used, specifically points on the sternocleidomastoid muscle.[33][34] 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.[34] By the standards of Evidence-based medicine, the quality of these studies can be considered poor (for example, Ishikawa has a study sample size of just six, is unblinded and without proper control), 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 produced.

Physical therapy or Occupational therapy is also used to treat nystagmus. Treatment consist of learning compensatory strategies to take over for the impaired system.

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.[2] Authors of another study in the United Kingdom estimated an incidence of 24 in 10,000 (~0.240 %), noting an apparently higher rate amongst white Europeans than in individuals of Asian origin.[35]

See also

Notes

  1. ↑ Note however that "dancing eyes" is also a common term for Opsoclonus myoclonus syndrome.

References

  1. ↑ Zahn JR (July 1978). "Incidence and characteristics of voluntary nystagmus". J. .jNeurol.Neurosurg. Psychiatr. 41 (7): 617–23. doi:10.1136/jnnp.41.7.617. PMC: 493105. PMID 690639.
  2. 1 2 "General Information about Nystagmus". American Nystagmus Network. February 21, 2002. Retrieved 2011-11-09.
  3. ↑ Weil, Andrew (2013). "Dealing with dancing eyes". Weil Lifestyle, LLC. Retrieved 2014-04-16.
  4. ↑ "Nystagmus". Medline Plus. February 27, 2013. Retrieved 2012-12-12.
  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. ↑ Markley, BA (2007). "Introduction to electronystagmography for END technologists". American Journal of Electroneurodiagnostic Technology 47 (3): 178–89. PMID 17982846.
  7. ↑ Mosca, F; Sicignano, S; Leone, CA (2003). "Benign positional paroxysmal vertigo: videonystagmographic study using rotatory test". Acta Otorhinolaryngologica Italica 23 (2): 67–72. PMID 14526552.
  8. ↑ Eggert, T (2007). "Eye movement recordings: methods". Developments in Ophthalmology 40: 15–34. doi:10.1159/0000100347. PMID 17314477.
  9. ↑ 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.
  10. ↑ Angelo Salami, Massimo Dellepiane, Edoardo Cervoni, Giancarlo Mascetti. Temporal analysis of the vestibular and optokinetic nystagmus. Volume 1240, October 2003, Pages 1333–1337. Oto-Rhino-Laryngology. Proceedings of the XVII World Congress of the International Federation of Oto-Rhino-Laryngological Societies (IFOS).
  11. ↑ "nystagmus". Retrieved 2007-06-07.
  12. ↑ Anagnostou, E (2006). "Positional nystagmus and vertigo due to a solitary brachium conjunctivum plaque". Journal of Neurology, Neurosurgery & Psychiatry 77 (6): 790–2. doi:10.1136/jnnp.2005.084624.
  13. ↑ 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.
  14. 1 2 "Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 179 Encyclopaedia Britannica, 1987
  15. ↑ Self, James; Lotery, Andrew (2007). "A Review of the Molecular Genetics of Congenital Idiopathic Nystagmus (CIN)". Ophthalmic Genetics 28 (4): 187–91. doi:10.1080/13816810701651233. PMID 18161616.
  16. ↑ Li, N; Wang, L; Cui, L; Zhang, L; Dai, S; Li, H; Chen, X; Zhu, L; Hejtmancik, JF; Zhao, K (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.
  17. ↑ Poopalasundaram, S; Erskine, L; Cheetham, M; Hardcastle, A (2005). "Focus on Molecules: Nyctalopin". Experimental Eye Research 81 (6): 627–8. doi:10.1016/j.exer.2005.07.017. PMID 16157331.
  18. ↑ Leroy, B P; Budde, B S; Wittmer, M; De Baere, E; Berger, W; Zeitz, C (2008). "A common NYX mutation in Flemish patients with X linked CSNB". British Journal of Ophthalmology 93 (5): 692–6. doi:10.1136/bjo.2008.143727. PMID 18617546.
  19. ↑ Peloquin, J.B.; Rehak, R.; Doering, C.J.; McRory, J.E. (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.
  20. ↑ Ganança, Fernando Freitas; Ganança, Ricardo; Ganança, Maurício M.; Korn, Gustavo P.; Dorigueto, Ricardo S. (2005). "É importante restringir a movimentação cefálica após a manobra de Epley?" [The number of procedures required to eliminate positioning nystagmus in benign paroxysmal positional vertigo]. Revista Brasileira de Otorrinolaringologia (in Portuguese) 71 (6): 769–75. doi:10.1590/S0034-72992005000600013. PMID 16878247.
  21. ↑ Lindgren, Stefan (1993). Kliniska färdigheter: Informationsutbytet mellan patient och läkare (in Swedish). Lund: Studentlitteratur. ISBN 91-44-37271-X.
  22. ↑ 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.
  23. ↑ 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.
  24. ↑ 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.
  25. ↑ Corbett, J (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.
  26. ↑ Muscular Dystrophy Association Press Release
  27. ↑ 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
  28. ↑ Groves, Nancy (March 15, 2006). "Many options to treat nystagmus, more in development". Ophthalmology Times.
  29. ↑ Biousse, V; Tusa, RJ; Russell, B; Azran, MS; Das, V; Schubert, MS; Ward, M; Newman, NJ (2004). "The use of contact lenses to treat visually symptomatic congenital nystagmus". Journal of Neurology, Neurosurgery & Psychiatry 75 (2): 314–6. doi:10.1136/jnnp.2003.010678. PMC: 1738913. PMID 14742616.
  30. ↑ Cerman, E. "Mini-telescopic eyeglasses suppress nystagmus". World Society of Pediatric Ophthalmology and Strabismus Conference in Barcelona 2015. Retrieved 26 January 2016.
  31. ↑ Kumar, Anand; Shetty, S; Vijayalakshmi, P; Hertle, RW (Nov–Dec 2011). "Improvement in visual acuity following surgery for correction of head posture in infantile nystagmus syndrome". J Pediatr Ophthalmol Strabismus 48 (6): 341–6. doi:10.3928/01913913-20110118-02. PMID 21261243.
  32. ↑ 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". J AAPOS 10 (6): 552–60. doi:10.1016/j.jaapos.2006.08.021. PMID 17189150.
  33. ↑ Ishikawa, S., et al. (1987). Treatment of nystagmus by acupuncture. Highlights in neuro-ophthalmology, 6th ed. pg 227–232.
  34. 1 2 Blekher, T. (1998). "Effect of acupuncture on foveation characteristics in congenital nystagmus". British Journal of Ophthamology. 82:115–120. Accessed May 6th, 2012:
  35. ↑ Sarvananthan, N.; Surendran, M.; Roberts, E. O.; Jain, S.; Thomas, S.; Shah, N.; Proudlock, F. A.; Thompson, J. R.; McLean, R. J.; Degg, C.; Woodruff, G.; Gottlob, I. (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.

External links

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