What is convergence retraction nystagmus?

Convergence Retraction Nystagmus: Diagnosis and Clinical Significance

Convergence retraction nystagmus (CRN) is a distinctive ocular movement disorder characterized by rapid, jerky convergent eye movements with retraction of the globes into the orbit, typically occurring during attempted upward gaze, and is a key diagnostic sign of dorsal midbrain syndrome (Parinaud syndrome) caused by lesions affecting the pretectal area and posterior commissure. 1, 2

Clinical Characteristics and Pathophysiology

• CRN presents as rapid, synchronous adducting movements of both eyes (convergence) often accompanied by retraction of the eyeballs into the orbit, particularly when the patient attempts to look upward 2
• It is distinct from other forms of nystagmus (manifest, latent, or manifest-latent) that may occur in patients with strabismus 3
• The pathophysiological mechanism involves either:
  • A disorder of the vergence system rather than the saccadic system, as evidenced by disconjugate horizontal and torsional components that align with normal vergence responses 2
  • Opposed adducting saccades that are slightly asynchronous, resulting from abnormal activation of convergence neurons 4, 5

Anatomical Localization

• CRN is a highly localizing neurological sign that indicates lesions affecting specific areas:

  • Pretectal areas of the dorsal midbrain 1
  • Posterior commissure 1, 2
  • Dorsomedial thalamic nuclei 1
  • Rostral interstitial nucleus of the medial longitudinal fascicle 2

• It is typically part of dorsal midbrain syndrome (Parinaud syndrome), which may also include:

  • Vertical gaze palsy (particularly upward gaze) 5
  • Light-near dissociation of pupils
  • Lid retraction (Collier's sign)

Etiology

• Most commonly associated with:
  • Vascular lesions (hemorrhagic or ischemic) affecting the dorsal midbrain 1
  • Space-occupying lesions such as pineal region tumors 5
  • Thalamic gliomas 5
  • Hydrocephalus causing compression of the dorsal midbrain
  • Multiple sclerosis
  • Arteriovenous malformations

Diagnostic Approach

• Neuroimaging is essential for patients presenting with CRN:

  • MRI of the brain (with particular attention to the midbrain, thalamus, and posterior fossa) is the preferred imaging modality 3
  • Contrast enhancement may be necessary if a suspicious lesion is identified 3
  • CT has limited value in the initial evaluation of nystagmus 3

• Clinical examination should include:

  • Assessment of ocular motility, particularly vertical gaze 6
  • Documentation of other associated neurological signs 6
  • Evaluation for signs of increased intracranial pressure if a space-occupying lesion is suspected

Clinical Significance and Prognosis

• While historically associated with poor prognosis due to its common occurrence with extensive neoplastic lesions, CRN can also occur with circumscribed vascular lesions that have a benign course 1
• The prognosis depends primarily on the underlying etiology:
  • Vascular lesions may have a favorable outcome 1
  • Neoplastic causes typically have a less favorable prognosis 5

Treatment Considerations

• Treatment is directed at the underlying cause rather than the nystagmus itself 6
• Surgical intervention may be necessary for space-occupying lesions
• For symptomatic management of visual disturbances related to nystagmus, medications such as 4-aminopyridine, memantine, gabapentin, or baclofen may be considered, though their efficacy specifically for CRN is not well established 6

Important Pitfalls to Avoid

• Do not confuse CRN with nystagmus blockage syndrome, which occurs in children with infantile esotropia who use excessive convergence to dampen nystagmus amplitude 3
• Avoid missing associated neurological signs that may help localize the lesion and determine the underlying etiology 6
• Remember that while CRN is classically associated with dorsal midbrain lesions, it can occasionally occur with lesions in other locations such as the thalamus 5