Definition

Pendular nystagmus is a form of involuntary eye movement characterized by oscillations of equal speed in both directions, resembling a pendulum's motion. It can affect one or both eyes and is typically seen in neurological or sensory disorders.

Key Features

1. Movement Characteristics:

   • Oscillations are sinusoidal, smooth, and of equal velocity in both directions.
   • Unlike jerk nystagmus, there is no fast or slow phase.

2. Direction:

   • Movements can be horizontal, vertical, torsional, or a combination.

3. Amplitude and Frequency:

   • Amplitude: Can range from fine (small movements) to coarse (large movements).
   • Frequency: Often slow, but varies depending on the underlying cause.

Etiology

Pendular nystagmus is often associated with conditions affecting the visual pathway, cerebellum, or brainstem. Common causes include:

1. Congenital:

   • Oculocutaneous albinism
   • Aniridia
   • Achromatopsia
   • Leber's congenital amaurosis

2. Acquired:

   • Neurological Disorders:
     • Multiple sclerosis (common in brainstem involvement)
     • Pelizaeus-Merzbacher disease
     • Brainstem or cerebellar lesions
   • Sensory Deprivation:
     • Long-standing visual impairment (e.g., retinal degeneration, optic nerve hypoplasia)

3. Drug-Induced:

   • Anticonvulsants, sedatives, or other medications affecting central nervous system function.

Pathophysiology

Pendular nystagmus arises from dysfunction in:

1. Afferent Visual Pathway:

   • Sensory deficits disrupt feedback loops essential for stable gaze.

2. Brainstem or Cerebellum:

   • Abnormal interactions in the ocular motor nuclei or vestibulocerebellar pathways.

3. Efferent Neural Mechanisms:

   • Impaired neural output to extraocular muscles.

Clinical Presentation

• Visual Symptoms:

  • Reduced visual acuity.
  • Oscillopsia (subjective sensation of a moving visual field).

• Systemic Features:

  • Neurological signs may accompany in acquired cases (e.g., ataxia in multiple sclerosis).

Diagnostic Evaluation

1. History:

   • Age of onset: Congenital vs. acquired.
   • Associated visual or neurological symptoms.
   • Family history of genetic disorders.

2. Ocular Examination:

   • Eye movement analysis to confirm pendular characteristics.

3. Neurological Examination:

   • Focus on cerebellar and brainstem signs.

4. Investigations:

   • Imaging: MRI brain to evaluate brainstem or cerebellar lesions.
   • Electrophysiology: Visual evoked potentials (VEP) and electroretinography (ERG) for sensory pathway assessment.
   • Genetic Testing: For congenital cases like oculocutaneous albinism.

Management

1. Treat Underlying Cause:

   • Multiple sclerosis: Immunomodulatory therapy.
   • Optic nerve conditions: Optimize visual input if possible.

2. Symptomatic Treatment:

   • Medications:
     • Gabapentin or memantine may reduce the amplitude of acquired pendular nystagmus.
   • Optical Aids:
     • Prism lenses to improve gaze stabilization.

3. Rehabilitation:

   • Visual and occupational therapy for optimizing functional vision.

4. Surgical Interventions:

   • Rarely considered, aimed at reducing amplitude in disabling cases.

Prognosis

• Congenital Cases: Often static but may improve with age and compensatory mechanisms.
• Acquired Cases: Variable prognosis depending on the reversibility of the underlying cause.

Key Takeaways for Practice

• Pendular nystagmus is often a sign of underlying sensory or neurological dysfunction; comprehensive evaluation is crucial.
• Multidisciplinary management is essential for optimizing outcomes, particularly in pediatric populations.
• Novel therapies targeting the neural pathways involved in nystagmus are under investigation and may hold promise for future management.

Clinical video courtesy: Dr Ahmed Reda