The cerebellum plays a pivotal role in the control of eye movements. Its core function is to optimize ocular motor performance so that images of objects of interest are promptly brought to the fovea – where visual acuity is best – and kept quietly there, so the brain has time to analyze and interpret the visual scene1.

The cerebellum has both immediate, on-line functions to make each individual movement accurate, and long-term, adaptive functions to keep ocular motor responses correctly calibrated to the stimuli that drive them.  The cerebellar cortex can be thought of as a parallel pathway that oversees and influences (via the projections of its Purkinje cells) the direct flow of information to and from the brain stem through the deep cerebellar nuclei2:

      Cerebellar Lesion


      Deficit


  Lesions of the flocculus/paraflocculus 


  Abnormal pursuit, with impaired visual suppression of the VOR
  Downbeat and rebound nystagmus.

 
  Lesions of the nodulus/uvula

 
  Periodic alternating nystagmus.

  Ocular motor vermis and the underlying fastigial nucleus


   Saccadic dysmetria, (hyper and hypometric saccades):

       Lesions of dorsal vermis: hypometric saccades

       Lesion of Fastigial N: hypermetric saccades

 

Other types of eye movement abnormalities also occur with cerebellar dysfunction but are poorly localized1:

  1. Various forms of saccadic intrusions, such as square-wave jerks, macrosaccadic oscillations, and ocular flutter, may be associated with cerebellar pathologies and often degrade vision.
  2. Skew deviation that often changes direction with horizontal eye position (alternating skew deviation) is seen with the abducting eye usually being higher, producing a pattern of right hyperdeviation in right gaze and left hyperdeviation in left gaze. It is presumed that the origin of the skew might be an imbalance in otolith-ocular projections to the cerebellum.
  3. Esotropia may be present, typically greater at distance and possibly due to impaired divergence.
  4. Head shaking-induced nystagmus (sometimes perverted, oppositely directed to the spontaneous nystagmus, or with a quick, large-amplitude reversal).
  5. Downbeating positional nystagmus
  6. Direction-changing, horizontal apogeotropic positional nystagmus (ie, beating to the sky with one ear down).
     
Figure 1. Topographical localization of cerebellar lesions

 

 

 

Figure 2. The cerebellar nuclei.

 

 

 

 

 

References

  1. Kheradmand A, Colpak AI, Zee DS. Eye movements in vestibular disorders. Handb Clin Neurol. 2016;137:103-17.
  2. Kheradmand A, Zee DS. Cerebellum and ocular motor control. Front Neurol. 2011;2:53.