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Anisocoria (pron.: //) is a condition characterized by an unequal size of the eye's pupils. Affecting 20% of 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 eye's pupils.
Anisocoria has various causes:
- Physiological Anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiologic anisocoria. In this condition the difference between pupils is usually less than 1 mm.
- Horner's Syndrome: is caused by a lesion of the sympathetic pathway which causes paresis (weakness) of the iris dilator muscle. Unilateral miosis, ptosis, and absence of sweating on the ipislateral face and neck make up the complete clinical presentation.
- Mechanical Anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.
- Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie's syndrome). Tonic pupil is characterized by delayed dilation of iris especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine.
- Oculomotor nerve palsy: Ischemia , intracranial aneurysm, head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults. In ischemic lesions of oculomotor nerve pupillary function is usually spared whereas in compressive lesions the pupil is involved.
- Pharmacological agents will cause anisocoria if instilled in one eye. Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, Dextromethorphan, and ergolines. Alkaloids present in plants of the genera Brugmansia and Datura, such as scopolamine, may also induce anisocoria.
Anisocoria causes range from benign (normal) to life-threatening conditions. Clinically, it is important to establish whether Anisocoria is more apparent in Dim or Bright light:
- Anisocoria which is greater in dim light suggests Horner's syndrome or mechanical Anisocoria. In Horner's syndrome sympathetic fibers have a defect, therefore pupil of the involved eye will not dilate in darkness.
- Anisocoria which is greater in bright light suggests Adie tonic pupil, pharmacologic dilation, Oculomotor nerve palsy, or damaged iris.
A relative afferent pupillary defect or 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 dissection) and Oculomotor nerve palsy (due to an 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 ptosis is present then the abnormally sized pupil can be presumed to be the one on the side of the ptosis. This is due to the fact that 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, etc can be a sign of hemorrhage, tumor or other pathology inside the brain pressing down on some critical nerves, being considered a neurosurgical emergency.
See also 
- Lam, BL; Thompson, HS; Corbett, JJ (1987 Jul 15). "The prevalence of simple anisocoria.". American journal of ophthalmology 104 (1): 69–73. PMID 3605282.
- John P.Whitcher, Paul Riordan-Eva. Vaughan & Asbury's general ophthalmology. (17th ed. ed.). McGraw-Hill Medical. p. 293. ISBN 978-0071443142.
- London, Richard; Ellen Richrer Erringer, Harry J. Wyafr, (March 1991). "Variation and Clinical Observation With Different Conditions of Illumination and Accommodation". Investigative Ophthalmology & Visual Science, 32 (3): 501–9.
- Anisocoria. Medscape Reference. Accessed April 15, 2012.
- . 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 More than one of
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- Medscape, online. "Anisocoria Clinical Presentation". Retrieved 25 November 2012.
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