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Infantile Nystagmus Syndrome (INS): for professionals


Overview

Prevalence
  • 12-14 in 10,000[1]
Symptoms
  • Visual impairment of variable severity
  • Reduced 3D vision
  • Photophobia
Ocular features
  • Nystagmus that develops at birth or shortly afterwards (less than 6 months)
  • May be associated with underlying ocular conditions
  • Variable reduction of visual acuity
  • Strabismus
  • Astigmatism
  • Compensatory head position
  • +/- Foveal hypoplasia
  • Primary INS in the absence of ocular or systemic abnormalities are termed Infantile Idiopathic Nystagmus
Systemic features
Key investigations
  • Orthoptic assessment and refraction
  • VEP: To investigate for chiasmal misrouting
  • ERG: Assess overall retinal function
  • OCT: To detect foveal hypoplasia and assess outer retinal integrity in cases of inherited retinal dystrophies
  • Eye movement recording: Characteristic increasing slow phase velocity
Molecular diagnosisNext generation sequencing
  • Targeted gene panels (nystagmus and eye movement disorders)
  • Whole exome sequencing
  • Whole genome sequencing
ManagementOcular
  • Amblyopia management
  • Correction of refractive errors
  • Surgical management may be required to address significant compensatory head postures utilised to optimise vision using a null point
  • Specific management depends on underlying cause
Systemic
  • Multidisciplinary approach if indicated
  • Early referral to practitioners familiar with young children with visual impairment to optimise development and access to education

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Clinical phenotype

Presenting features

Infantile nystagmus syndrome (INS) is an umbrella term used to describe different forms of infantile nystagmus (with or without sensory defects) characterized by an increasing slow phase velocity.[2] The nystagmus in INS is predominantly a horizontal conjugate oscillation of the eyes. These oscillations usually develop at birth or shortly afterwards (less than 6 months) and persists throughout life.

Other ocular features

  • Refractive errors
  • Strabismus (uncommon; affecting approx. 10% of individuals)
  • Foveal hypoplasia[3]
  • Photophobia
  • Compensatory head posture to achieve null point (an area of minimum nystagmus and better vision)

Oscillopsia is rarely described by INS patients due to stabilising of moving images through either extra-retinal feedback[4] or periods of foveation.[2] Affected individuals may perceive the moving images if the nystagmus waveform increases (speed and position) in different positions of gaze.

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Differential diagnosis

INS may be idiopathic (termed Infantile Idiopathic Nystagmus) or it can be associated with the following conditions:

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Key investigations

Ocular

All children affected by nystagmus should undergo a general ophthalmological assessment. If systemic features are detected, patients should be referred to the relevant specialties. Children may also benefit from a paediatric overview.

1) Orthoptic assessment and refraction

To assess current level of vision and determine if amblyopia therapy and/or refractive correction are required to optimise vision.

2) Optical coherence tomography (OCT) and fundus autofluorescence (FAF) imaging

OCT can detect the presence/absence of foveal hypoplasia to support the clinical diagnosis and document its severity if present.[3] It can also be used to assess the outer retinal integrity in cases of inherited retinal dystrophies along with FAF imaging.

3) Electrophysiology

Visual evoked potentials can be requested to look for evidence of chiasmal misrouting. Full-field and pattern electroretinogram (ERG) readings are required to exclude retinal and/or macular dystrophies.

4) Eye movement recordings

INS waveforms are pathognomonic. The recordings tend to demonstrate conjugate horizontal oscillations with either a jerk or pendular waveform and the slow phase typically has an increasing velocity.

A right beating jerk nystagmus with accelerating exponential slow phases to the left. Red lines mark the period of foveation. Green dotted lines denote the fast phase and the orange dotted lines denote the slow phase.

Credit: Mr Vijay Tailor-Hamblin, Clinical PhD Fellow and Extended Role Orthoptist, Moorfields Eye Hospital, London 

In some very early cases where nystagmus may be absent or not prominent, saccadic instabilities (square wave jerks) can be noted instead before evolving to more typical waveforms (conjugate pendular/jerk types) as the child gets older.[6]

Systemic

INS can be associated with ocular or systemic causes. Certain red flag signs may indicate an acquired pathology instead that will require neuro-imaging[7,8]:

  • Later onset nystagmus (in the absence of signs in keeping with an ocular disorder)
  • Constant oscillopsia in older children/adults
  • Dysconjugate/gaze evoked/see-saw/convergence-retraction nystagmus
  • Vertical/torsional nystagmus (in the absence of retinal pathology)
  • Presence of neurological signs and/or a systemically unwell child

If these features are absent, referral to a paediatrician and other relevant specialists should be considered if patients show signs of developmental issues or based on the results of genetic testing.

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Diagnosis

Diagnosis of INS is usually made clinically through eye movement recordings and full ophthalmological examination. Genetic testing should be undertaken to obtain a molecular diagnosis which can help in directing further clinical management, facilitating genetic counselling and providing accurate advice on prognosis and future family planning.

This can be achieved through a variety of next generation sequencing (NGS) methods:

  • Targeted gene panels (nystagmus and eye movement disorders)
  • Whole exome sequencing
  • Whole genome sequencing

Related links

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Management

General management of INS includes refractive treatment, amblyopia therapy, medical and surgical interventions. Further details can be found in the management section of Infantile Idiopathic Nystagmus. Specific management depends on the underlying ocular or systemic cause.

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Current research in nystagmus

Currently there is only one RCT recruiting in Toronto investigating the effect of a biofeedback system to improve visual outcome in idiopathic nystagmus (NCT 04142307). Other research areas have included the use of refractive[9-11], drug[12,13] and surgical[14-16] treatments to improve visual outcome. Other pre-clinical work that is being undertaken is the investigation of visual crowding in idiopathic nystagmus and how the basis of these deficit reflects the eye movements seen in nystagmus[17].

Related links

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Further information and support

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References

  1.  Sarvananthan N, Surendran M, Roberts E, et al. The Prevalence of Nystagmus: The Leicestershire Nystagmus Survey. Investigative ophthalmology & visual science. 2009;50:5201-6. doi:10.1167/iovs.09-3486
  2.  Thomas MG, Maconachie G, Hisaund M, Gottlob I. FRMD7-related infantile nystagmus. GeneReviews®[Internet]. University of Washington, Seattle; 2018
  3.  Thomas MG, Crosier M, Lindsay S, et al. Abnormal retinal development associated with FRMD7 mutations. Human molecular genetics. 2014;23(15):4086-4093
  4.  Abadi RV, Whittle JP, Worfolk R. Oscillopsia and tolerance to retinal image movement in congenital nystagmus. Investigative Ophthalmology & Visual Science. 1999;40(2):339-345
  5.  Gottlob I. Nystagmus. Curr Opin Ophthalmol. Oct 2000;11(5):330-5
  6.  Gottlob I. Infantile nystagmus. Development documented by eye movement recordings. Invest Ophthalmol Vis Sci. Mar 1997;38(3):767-73
  7.  Ospina LH. Dealing with Nystagmus. J Binocul Vis Ocul Motil. Oct-Dec 2018;68(4):99-109. doi:10.1080/2576117x.2018.1493311
  8.  Self JE, Dunn MJ, Erichsen JT, et al. Management of nystagmus in children: a review of the literature and current practice in UK specialist services. Eye (Lond). Sep 2020;34(9):1515-1534. doi:10.1038/s41433-019-0741-3
  9.  Stahl JS, Plant GT, Leigh RJ. Medical treatment of nystagmus and its visual consequences. Journal of the Royal Society of Medicine. May 2002;95(5):235-7
  10.  Theodorou M, Quartilho A, Xing W, et al. Soft contact lenses to optimize vision in adults with idiopathic infantile nystagmus: a pilot parallel randomized controlled trial. Strabismus. 2018;26(1):11-21
  11.  Jayaramachandran P, Proudlock FA, Odedra N, Gottlob I, McLean RJ. A randomized controlled trial comparing soft contact lens and rigid gas-permeable lens wearing in infantile nystagmus. Ophthalmology. 2014;121(9):1827-1836
  12.  Sarvananthan N, Proudlock FA, Choudhuri I, Dua H, Gottlob I. Pharmacologic Treatment of Congenital Nystagmus. Archives of Ophthalmology. 2006;124(6):916-918. doi:10.1001/archopht.124.6.916
  13.  Shery T, Proudlock FA, Sarvananthan N, McLean RJ, Gottlob I. The effects of gabapentin and memantine in acquired and congenital nystagmus: a retrospective study. Br J Ophthalmol. Jul 2006;90(7):839-43. doi:10.1136/bjo.2005.086322
  14.  Dell’Osso LF, Orge FH, Jacobs JB. Effects of augmented tenotomy and reattachment in the infantile nystagmus syndrome. Digit J Ophthalmol. 2016;22(1):12-24. doi:10.5693/djo.01.2016.01.002
  15.  Lingua RW, Liu CY, Gerling A, Zhang Z, Nalbandian A. Myectomy of the Extraocular Muscles Without Reattachment as a Surgical Treatment for Horizontal Nystagmus. J Pediatr Ophthalmol Strabismus. May 01 2016;53(3):156-66. doi:10.3928/01913913-20160302-01
  16.  Lingua RW, Liu CY, Gerling A, Zhang Z, Nalbandian A. Further Considerations in the Management of Nystagmus with Myectomy. J Pediatr Ophthalmol Strabismus. Jul 1 2016;53(4):255. doi:10.3928/01913913-20160610-01
  17.  Tailor V, Dahlmann-Noor AH, Theodorou M, Greenwood J. Visual crowding in congenital nystagmus, sensory deficit or image motion? Investigative Ophthalmology Visual Science. 2018;59(9):1080-1080

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Updated on November 30, 2020
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