Causes

In the absence of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve (parasympathetic fibers) or the sympathetic pathways. Physical lesions or drugs may cause anisocoria by disrupting these pathways.
It may be associated with adie syndrome

Adie syndrome

Adie syndrome, sometimes known as Holmes-Adie's syndrome or Adie's Tonic Pupil, is a neurological disorder characterized by a tonically dilated pupil. It is named after the British neurologist William John Adie...

.

Some examples of drugs which may affect the pupils include pilocarpine

Pilocarpine

Pilocarpine is a parasympathomimetic alkaloid obtained from the leaves of tropical American shrubs from the genus Pilocarpus. It is a non-selective muscarinic receptor agonist in the parasympathetic nervous system, which acts therapeutically at the muscarinic acetylcholine receptor M3 due to its...

, cocaine

Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...

, tropicamide

Tropicamide

Tropicamide is an anticholinergic used as a mydriatic. In Russia, it is used to some degree as an inexpensive recreational drug...

, MDMA, Dextromethorphan

Dextromethorphan

Dextromethorphan is an antitussive drug. It is one of the active ingredients in many over-the-counter cold and cough medicines, such as Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, and others, including generic labels. Dextromethorphan has also found other uses in medicine, ranging...

 and scopolamine

Scopolamine

Scopolamine, also known as levo-duboisine, and hyoscine, is a tropane alkaloid drug with muscarinic antagonist effects. It is among the secondary metabolites of plants from Solanaceae family of plants, such as henbane, jimson weed and Angel's Trumpets , and corkwood...

. Such alkaloids present in plants of the genus Brugmansia

Brugmansia

Brugmansia is a genus of seven species of flowering plants in the family Solanaceae, native to subtropical regions of South America, along the Andes from Colombia to northern Chile, and also in southeastern Brazil. They are known as Angel's Trumpets, sharing that name with the closely related genus...

 may also induce anisocoria.

Additionally, dilation of the pupil is termed mydriasis

Mydriasis

Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...

 and constriction of the pupil is termed miosis

Miosis

Miosis is the constriction of the pupil of the eye to two millimeters or less...

.

Anisocoria (up to 0.5mm) can also be a benign and idiopathic condition, sometimes referred as physiological anisocoria.

Interpretation

Clinically, it is important to establish which of the two pupils is behaving abnormally.

• If the smaller of the two pupils is the abnormal one, dimming the ambient light will not cause it to dilate, in which case a defect in sympathetic fibers is suspected, as seen in Horner's syndrome
  Horner's syndrome
  Horner's syndrome is the combination of drooping of the eyelid and constriction of the pupil , sometimes accompanied by decreased sweating of the face on the same side; redness of the conjunctiva of the eye is often also present...
  
  .
• Alternatively, if the abnormal pupil is the larger one, it will fail to contract in response to light, raising suspicion for a parasympathetic nerve defect, possibly an oculomotor nerve
  Oculomotor nerve
  The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...
  
   palsy.

A relative afferent pupillary defect or RAPD also known as a Marcus Gunn pupil

Marcus Gunn pupil

Marcus Gunn pupil is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less when a bright light is swung from the unaffected eye to the affected eye...

 does not cause anisocoria.

When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis

Ptosis (eyelid)

Ptosis is a drooping of the upper or lower eyelid. The drooping may be worse after being awake longer, when the individual's muscles are tired. This condition is sometimes called "lazy eye", but that term normally refers to amblyopia...

 is present then the abnormally sized pupil can be presumed to be the one on the side of the ptosis, as a Horner's syndrome [sympathetic lesion], and an Oculomotor nerve lesion both cause ptosis.

Anisocoria in the presence of confusion, decreased mental status, severe headache, etc. can be a sign of blood, tumour or other pathology inside the brain pressing down on some critical nerves. This is a neurosurgical emergency requiring emergency treatment and possibly surgery.

See also

• Adie syndrome
  Adie syndrome
  Adie syndrome, sometimes known as Holmes-Adie's syndrome or Adie's Tonic Pupil, is a neurological disorder characterized by a tonically dilated pupil. It is named after the British neurologist William John Adie...
  
  
• Cycloplegia
  Cycloplegia
  Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation.-Anatomy:The iris is the heavily pigmented colored part of the eye. It has a contractile diaphragm in front of the lens with a central opening called the pupil...
  
  
• Marcus Gunn pupil
  Marcus Gunn pupil
  Marcus Gunn pupil is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less when a bright light is swung from the unaffected eye to the affected eye...
  
  
• Miosis
  Miosis
  Miosis is the constriction of the pupil of the eye to two millimeters or less...
  
  
• Mydriasis
  Mydriasis
  Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
  
  
• Parinaud's syndrome
  Parinaud's syndrome
  Parinaud's Syndrome, also known as dorsal midbrain syndrome is a group of abnormalities of eye movement and pupil dysfunction. It is caused by lesions of the upper brain stem and is named for Henri Parinaud , considered to be the father of French ophthalmology...
  
  

External links

• http://www.kellogg.umich.edu/theeyeshaveit/symptoms/anisocoria.html