Infantile Nystagmus Syndrome (INS): for professionals

• Overview
• Clinical phenotype
• Differential diagnosis
• Key investigations
• Diagnosis
• Management
• Current research
• Further information and support
• References

---

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	May be associated with systemic conditions such as albinism, Alström syndrome and Down syndrome
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 diagnosis	Next generation sequencing Targeted gene panels (nystagmus and eye movement disorders) Whole exome sequencing Whole genome sequencing
Management	Ocular 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

Jump to top

---

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.

Jump to top

---

Differential diagnosis

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

• Syndromic and non-syndromic oculocutaneous albinism or ocular albinism
• Aniridia
• Retinopathy of prematurity
• Syndromic and non-syndromic inherited retinal dystrophies (e.g. Leber congenital amaurosis, Alström syndrome etc)
• Ocular coloboma
• Congenital cataract
• Optic disc atrophy
• Optic nerve hypoplasia
• Spasmus Nutans^[5]
• Down Syndrome
• Cerebral palsy

Jump to top

---

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.

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.

Jump to top

---

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

• Genomics England PanelApp for albinism or congenital nystagmus
• Clinical genetic testing: for professionals

Jump to top

---

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.

Jump to top

---

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

• Research Opportunities at Moorfields Eye Hospital UK
• Searching for current clinical research or trials

Jump to top

---

Further information and support

• Nystagmus Network
• Albinism Fellowship
• Royal National Institute of Blind People (RNIB)
• IN-vision

Jump to top

---

References

Jump to top