What causes nystagmus in children

What is Nystagmus in Children?

Nystagmus is an involuntary, rhythmic, and repetitive movement of the eyes. This 'dancing eyes' phenomenon can cause the eyes to move back and forth, up and down, or in a circular pattern. It's often described as the eyes oscillating or shaking. While it can occur at any age, nystagmus in children is a significant concern as it can impact visual development and overall quality of life.

Causes of Nystagmus in Children

The causes of nystagmus in children are diverse, ranging from congenital conditions to acquired neurological disorders. Understanding these causes is crucial for diagnosis and management.

Congenital Nystagmus

The most common form of nystagmus in children is congenital nystagmus, which is present at birth or develops within the first few months of life (typically by 6 months). In many of these cases, the nystagmus is directly related to an underlying vision impairment. The brain doesn't receive clear, stable images from one or both eyes, and the eyes develop abnormal movements as the brain tries to scan for visual information or compensate for the lack of clear input. Common causes of vision impairment leading to congenital nystagmus include:

• Albinism: This genetic condition is characterized by a lack of pigment in the skin, hair, and eyes. The absence of pigment in the retina affects its development and function, leading to reduced visual acuity and often congenital nystagmus. It's estimated that 10-20% of children with congenital nystagmus have albinism.
• Cataracts: Clouding of the lens of the eye, present from birth, can significantly block light from reaching the retina, causing poor vision and nystagmus. Early detection and surgical intervention are vital.
• Optic Nerve Hypoplasia (ONH): This is a condition where the optic nerve, which transmits visual information from the eye to the brain, is underdeveloped. This leads to reduced vision and frequently co-occurs with nystagmus.
• Aniridia: Absence of the iris, the colored part of the eye, can lead to light sensitivity and poor vision, contributing to nystagmus.
• Corneal Opacity: Clouding of the cornea, the clear outer layer of the eye, can also impede vision.
• High Refractive Errors: Severe farsightedness (hyperopia) or nearsightedness (myopia) that is not corrected can also be a contributing factor.
• Other Retinal Abnormalities: Various rare genetic conditions affecting the retina can cause reduced vision and nystagmus.

In a significant number of congenital nystagmus cases, the exact cause of the vision impairment may not be identifiable. This is referred to as idiopathic infantile nystagmus.

Acquired Nystagmus

While less common in children than congenital nystagmus, acquired nystagmus can develop later in childhood or adolescence due to various factors:

• Neurological Conditions: Disorders affecting the brain's pathways involved in vision, eye movement control, or balance can cause nystagmus. This includes conditions like:
  • Brain tumors
  • Multiple sclerosis (MS)
  • Head injuries (trauma)
  • Certain genetic neurological disorders
  • Developmental delays or cerebral palsy
  • Inner ear problems (vestibular system dysfunction)
• Medications and Toxins: In rare instances, certain medications or exposure to toxins can affect the nervous system and lead to nystagmus.
• Vision Loss: If a child develops significant vision loss later in childhood due to conditions like Leber congenital amaurosis or severe optic nerve damage, acquired nystagmus may develop as a secondary symptom.

Hereditary Factors

Nystagmus can sometimes run in families, suggesting a genetic predisposition. This can be linked to inherited conditions like albinism or specific forms of hereditary nystagmus where the cause is not tied to another identifiable condition.

The 'Null Zone'

Children with nystagmus often develop a 'null zone' – a specific head position where the eye movements are minimized, and their vision is temporarily clearer. They may instinctively adopt this head posture (head turn or tilt) to improve their visual acuity. This is a compensatory mechanism rather than a cause of nystagmus itself.

Diagnosis and Management

Diagnosing the cause of nystagmus involves a comprehensive eye examination by an ophthalmologist and potentially a neurological assessment. Treatment focuses on addressing the underlying cause if possible, managing associated vision problems with glasses or contact lenses, and sometimes surgical interventions to improve head posture and visual comfort. Therapies like vision therapy may also be recommended.