Pupil: anisocoria in Horses (Equis) | Vetlexicon
equis - Articles

Pupil: anisocoria

ISSN 2398-2977

Podcast: Pupil: anisocoria


  • Unequal or asymmetrical pupils   Pupil: anisocoria    Pupil: normal  .
  • Cause: 2 basic etiologies:
  • Disturbance of neurologic pathways controlling pupillary behavior including the retina, optic nerve, midbrain, and oculomotor nerve.
  • Mechanical or structural problems of the iris.
  • Diagnosis: differentiation of the causes of anisocoria requires a thorough neurologic and ophthalmologic examination and a clear understanding of normal pupillary neuroanatomy.
  • Treatment: depends upon the specific diagnosis.
  • Prognosis: depends upon the specific diagnosis.


Neurologic disfunction Static anisocoria
  • Traumatic, infection or vascular lesions of:
  • Oculomotor system - unilateral retinal or optic nerve/tract disease.
  • Retrobulbar area.
  • Brainstem, midbrain or cerebellar lesions.
  • Cervical spinal cord.
  • Cervical sympathetic trunk.
  • Guttural pouch.
  • Pharmacologic affect on pupil:
  • Mydriasis - due to blockade, eg atropine drops   Atropine sulfate  .
  • Mydriasis due to stimulation, eg phenylephrine .
  • Miosis due to stimulation, eg pilocarpine .
  • Glaucoma will have a dilated pupil, and uveitis a miotic pupil.
  • Dynamic - contraction anisocoria
  • More extensive direct Pupillary Light Reflex (PLR) in light stimulated eye compared to consensual response   Neurology: vision testing - overview  .
  • Problems of the iris
  • Congenital
  • Iris coloboma .
  • Iris hypoplasia (aniridia) .
  • Acquired
  • Anterior uveitis .
  • Corneal pain (reflex uveitis) .
  • Synechiae .
  • Glaucoma .


  • Pharmacologic testing:
  • Differentiates central, pre- and post-ganglionic efferent autonomic nerve lesions.
  • Postganglionic denervation supersensitivity.
  • Response to topical administration of 1% phenylephrine or varying doses of pilocarpine .


  • Depends upon specific diagnosis - see Etiology.


  • Depends upon specific diagnosis - see Etiology.

Further Reading


Refereed papers

Other sources of information

  • Brooks D E (1999) Equine Ophthalmology. In: Vet Ophthalmology. 3rd edn. Ed: Gelatt K N. Lippincott, USA. pp 1053-1116.