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Anisocoria (IPA: //) 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.
Anisocoria has various causes:
- Physiological anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiological anisocoria. In this condition, the difference between pupils is usually less than 1 mm.
- Horner's syndrome
- 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 the 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.
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:
- Anisocoria which is greater in dim light suggests Horner's syndrome or mechanical anisocoria. In Horner's syndrome sympathetic fibers have a defect, therefore the 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 (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 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 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, 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.
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- . 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
- Medscape, online. "Anisocoria Clinical Presentation". Retrieved 25 November 2012.
- "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