Nystagmus

Nystagmus

Horizontal optokinetic nystagmus, a normal (physiological) form of nystagmus
ICD-10	H55, H81.4
ICD-9	379.50, 794.14
DiseasesDB	23470
MeSH	D009759

Nystagmus /nɪˈstæɡməs/ is a condition of involuntary eye movement, acquired in infancy or later in life, that may result in reduced or limited vision.^[1]

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 or alcohol. Previously considered untreatable, in recent years several pharmaceutical drugs have been identified for treatment of Nystagmus.

Prevalence

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.^[1] 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.^[2]

Diagnosis

Nystagmus is very noticeable but little recognized. Nystagmus can be clinically investigated by using a number of non-invasive standard tests. The simplest one is Caloric reflex test, in which one external auditory meatus is irrigated with warm or cold water or air. The temperature gradient provokes the stimulation of the horizontal semicircular canal and the consequent nystagmus.

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),^[3] or even less invasive devices called videonystagmograph (VNG),^[4] 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.^[5]

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 their 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.^[6]

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 movement (SPEV) and the fast phase eyes velocity (FPEV) are related to each other and can be considered as a measurement of the efficiency of the system stimulus/response^[7].

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.^[8]

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.
• 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.
  • 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 vestibular apparatus.
  • Positional nystagmus occurs when a person's head is in a specific position.^[9] 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.

Physiologic nystagmus

Physiologic 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,^[10] 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.

• 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.^[11]

• 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.^[11]

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, and the dissociative anesthetics [PCP]).

Congenital nystagmus occurs more frequently than acquired nystagmus. It can be insular or accompany other disorders (such as micro-ophthalmic anomalies or Down Syndrome). Congenital 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 congenital nystagmus include the following: Infantile: Albinism Aniridia Bilateral congenital cataracts 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 monophthalmos 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.[12][13] Congenital 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).[14][15] CSNB-2 involves mutations of CACNA1F, a voltage-gated calcium channel that, when mutated, does not conduct ions.[16] Acquired Nystagmus may be acquired from: Diseases. Some of the diseases that present nystagmus as a pathological sign: Albinism Aniridia Benign Paroxysmal Positional Vertigo [17] Brain tumors (Medulloblastoma, Astrocytoma, or other tumors in the posterior fossa. Head trauma Lateral medullary syndrome Ménière's disease and other balance disorders Multiple sclerosis Optic nerve hypoplasia Pelizaeus-Merzbacher disease Superior canal dehiscence syndrome Stroke (the most common cause in older people) Tullio phenomenon Wernicke-Korsakoff syndrome Whipple's disease

Toxic/metabolic reasons could be the result of the following: Alcohol intoxication Barbiturates Benzodiazepines Ketamine Lithium Lysergic acid diethylamide (LSD) Methylenedioxymethamphetamine (MDMA) Methylenedioxyamphetamine (MDA) Other anticonvulsants or sedatives Phencyclidine (PCP) Phenytoin (Dilantin) Salicylates SSRIs Thiamine deficiency Wernicke's encephalopathy Central nervous system (CNS) disorders, such as with a cerebellar problem, the nystagmus can be in any direction including horizontal. Purely vertical nystagmus is usually central in origin, but it is also a frequent adverse effect of high phenytoin toxicity. Causes include: Cerebellar ataxia Chiari Malformation Multiple sclerosis Stroke Thalamic hemorrhage Trauma Tumor Other causes Non-physiologic Trochlear nerve malfunction[18] Vestibular Pathology (Ménière's disease, SCDS (superior canal dehiscence syndrome), BPPV, Labyrinthitis)

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,^[19] levetiracetam, 3,4-diaminopyridine, 4-aminopyridine, and acetazolamide.^[20] Several therapeutic approaches, such as contact lenses,^[21] drugs, surgery, and low vision rehabilitation have also been proposed.

Clinical trials of a surgery to treat nystagmus (known as tenotomy) concluded in 2001. Tenotomy is being performed regularly at the University of Pittsburgh Children's Hospital and by a handful of surgeons 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.^{[medical citation needed]}

Nystagmus and alcohol

Main article: Positional alcohol nystagmus

In police work, testing for horizontal gaze nystagmus is one of a battery of field sobriety tests used by 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 field sobriety test studies published by the National Highway Traffic Safety Administration have never been peer reviewed and attempts to duplicate the study results have been unsuccessful.^[22]

The horizontal gaze nystagmus test has been highly criticized and major errors in the testing methodology and analysis found.^[23][24] 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 BAC than other standard field sobriety tests.^[25]

Research

Several universities are researching nystagmus and are looking for volunteers to take part in research activities.

See also

• Eye care professional
• Opsoclonus
• Optokinetic nystagmus
• Orthoptist
• Visual impairment

References

1. ^ ^{a b} "General Information about Nystagmus". American Nystagmus Network. February 21, 2002. http://www.nystagmus.org/aboutn.html. Retrieved 2011-11-9. 
2. ^ Sarvananthan, N.; Surendran, M.; Roberts, E. O.; Jain, S.; Thomas, S.; Shah, N.; Proudlock, F. A.; Thompson, J. R. et al. (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. 
3. ^ Markley, BA (2007). "Introduction to electronystagmography for END technologists". American journal of electroneurodiagnostic technology 47 (3): 178–89. PMID 17982846. 
4. ^ 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. 
5. ^ Eggert, T (2007). "Eye movement recordings: methods". Developments in ophthalmology 40: 15–34. doi:10.1159/0000100347. PMID 17314477. 
6. ^ 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1757336. 
7. ^ 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).
8. ^ "nystagmus". http://www.drhull.com/EncyMaster/N/nystagmus.html. Retrieved 2007-06-07. 
9. ^ 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. 
10. ^ 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. 
11. ^ ^{a b} "Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 179 Encyclopaedia Britannica, 1987
12. ^ 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. 
13. ^ Li, N; Wang, L; Cui, L; Zhang, L; Dai, S; Li, H; Chen, X; Zhu, L et al. (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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2324116. 
14. ^ 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. 
15. ^ 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. 
16. ^ 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. 
17. ^ Ganança, Fernando Freitas; Simas, 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]" (in Portuguese). Revista Brasileira de Otorrinolaringologia 71 (6): 769–75. doi:10.1590/S0034-72992005000600013. PMID 16878247. 
18. ^ Lindgren, Stefan (1993) (in Swedish). Kliniska färdigheter: Informationsutbytet mellan patient och läkare. Lund: Studentlitteratur. ISBN 91-44-37271-X. ^{[page needed]}
19. ^ 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. 
20. ^ 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&ref=25. 
21. ^ 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1738913. 
22. ^ Cole S, Nowaczyk RH (August 1994). "Field sobriety tests: are they designed for failure?". Perceptual and Motor Skills 79 (1 Pt 1): 99–104. doi:10.2466/pms.1994.79.1.99. PMID 7991338. 
23. ^ 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. 
24. ^ 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. 
25. ^ 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. 

External links

• American Nystagmus Network — US-based support organization
• Nystagmus Network UK — UK-based support organisation
• nystagmus.co.uk — a teenager's experiences of nystagmus and a friendly forum
• The Shifty Eyes Blog — a blog about life with nystagmus
• Nystagmus Blog — A blog about nystagmus, A parent’s perspective
• GeneReview/NIH/UW entry on FRMD7-Related Infantile Nystagmus
• Current UK Research Projects
• MeSH Physiologic+Nystagmus