Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting 20% of the population, it can be an entirely harmless condition or a symptom of more serious medical problems.



Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes.[1]

Anisocoria has various causes:[2]


Causes of anisocoria range from benign (normal) to life-threatening conditions. Clinically, it is important to establish whether anisocoria is more apparent in dim or bright light to clarify if the larger pupil or smaller pupil is the abnormal one.

  • Anisocoria which is worsened (greater asymmetry between the pupils) in the dark suggests the small pupil (which should dilate in dark conditions) is the abnormal pupil and suggests Horner's syndrome or mechanical anisocoria. In Horner's syndrome sympathetic nerve fibers have a defect, therefore the pupil of the involved eye will not dilate in darkness. If the smaller pupil dilates in response to instillation of apraclonidine eye drops, this suggests Horner's syndrome is present.
  • Anisocoria which is greater in bright light suggests the larger pupil (which should constrict in bright conditions) is the abnormal pupil. This may suggest Adie tonic pupil, pharmacologic dilation, oculomotor nerve palsy, or damaged iris.

A relative afferent pupillary defect (RAPD) also known as a Marcus Gunn pupil does not cause anisocoria.

Some of the causes of anisocoria are life-threatening, including Horner's syndrome (which may be due to carotid artery dissection) and oculomotor nerve palsy (due to a brain aneurysm, uncal herniation, or head trauma).

If the examiner is unsure whether the abnormal pupil is the constricted or dilated one, and if a one-sided drooping of the eyelid is present then the abnormally sized pupil can be presumed to be the one on the side of the ptosis. This is because Horner's syndrome and oculomotor nerve lesions both cause ptosis.

Anisocoria is usually a benign finding, unaccompanied by other symptoms (physiological anisocoria). Old face photographs of patients often help to diagnose and establish the type of anisocoria.

It should be considered an emergency if a patient develops acute onset anisocoria. These cases may be due to brain mass lesions which cause oculomotor nerve palsy. Anisocoria in the presence of confusion, decreased mental status, severe headache, or other neurological symptoms can forewarn a neurosurgical emergency. This is because a hemorrhage, tumor or another intracranial mass can enlarge to a size where the third cranial nerve (CN III) is compressed, which results in uninhibited dilatation of the pupil on the same side as the lesion.[7]

  • English singer David Bowie exhibited anisocoria, owing to a teenage injury.[8]
  • In the season 10 Big Bang Theory Comic-Con special, Steve Molaro told a story about how he first met actor Judd Hirsch and was taken aback by his dilated pupil. One of the other writers researched it and discovered that Judd Hirsch has anisocoria.
  • American actress Melissa Benoist developed this condition in 2015.


Anisocoria is composed of prefix, root and suffix:

  • prefix: aniso- from the Greek language (meaning: unequal), which in turn comes from an: meaning not and iso: meaning equal
  • the root word: cor, from the Greek word "korē" meaning: pupil of the eye
  • -ia, which is a Latin suffix meaning: disease; pathological or abnormal condition

Thus, anisocoria means the condition of unequal pupil(s).

See also


  1. Lam, BL; Thompson, HS; Corbett, JJ (Jul 15, 1987). "The prevalence of simple anisocoria". American Journal of Ophthalmology. 104 (1): 69–73. doi:10.1016/0002-9394(87)90296-0. PMID 3605282.
  2. John P.Whitcher; Paul Riordan-Eva (2007-10-18). Vaughan & Asbury's general ophthalmology (17th ed.). McGraw-Hill Medical. p. 293. ISBN 978-0071443142.
  3. London, Richard; Richrer Erringer, Ellen; Wyafr, Harry J. (March 1991). "Variation and Clinical Observation With Different Conditions of Illumination and Accommodation". Investigative Ophthalmology & Visual Science. 32 (3): 501–9.
  4. Anisocoria. Medscape Reference. Accessed April 15, 2012.
  5. . It is also seen in some people who consume diphenydramine (brand name "Benadryl") for an extended period of time, or if an astringent eye drop like Visine is used in one eye and not the other, often in concurrence with the presence of contact lenses.van der Donck, I.; Mulliez, E.; Blanckaert, J. (2004), "Angel's Trumpet (Brugmansia arborea) and mydriasis in a child - A case report", Bulletin de la Societe Belge d'Ophtalmologie, 292: 53–56, ISSN 0081-0746
  6. "Anisocoria Differential Diagnoses". Retrieved 3 June 2017.
  7. Medscape, online. "Anisocoria Clinical Presentation". Retrieved 25 November 2012.
  8. Hunt, Kevin (January 11, 2016). "The remarkable story behind David Bowie's most iconic feature". The Conversation. Retrieved January 17, 2016.

Further reading

  • "Anisocoria." "Stedman's Medical Dictionary, 27th ed." (2000). ISBN 0-683-40007-X
  • Victor, Maurice and Allan H. Ropper. "Adams and Victor's Principles of Neurology, 7th ed." (2001). ISBN 0-07-067497-3
External resources
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