_____________________________________________________________________________________________________________________________________________

I ANATOMY                

 

II PHYSIOLOGY OF        EYE MOVEMENTS 

III EXAMINATION: EYE MOVEMENTS & NYSTAGMUS 

IV FIXATION INSTABILITY   

V SUPRANUCLEAR to NUCLEAR  

 VI VESTIBULAR     SYSTEM 

VIII CN PALSIES, VISUAL FIELDS, PUPIL & THE EYE

_____________________________________________________________________________________________________________________________________________

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.

      Cerebellar Lesion


      Deficit

  Lesions of the flocculus/paraflocculus 

  Saccadic pursuit, impaired visual suppression of the VOR, and downbeat rebound nystagmus.

  Lesions of the nodulus/uvula

  Periodic alternating nystagmus.

  Ocular motor vermis (Lobules VI and VII) 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 in these patients
  2. Skew deviation that often changes sense with horizontal eye position (alternating skew deviation) is seen with the abducting eye is usually 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) and positional nystagmus also have been reported in cerebellar patients.
  5. Downbeating positional nystagmus
  6. Direction-changing, horizontal apogeotropic positional nystagmus (i.e., beating to the sky with one ear down).

 

Figure 1. 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.