anisocoria

Physiological anisocoria is when human pupils differ in size.

Pharmacological agents will cause anisocoria if instilled in one eye.

It should be considered an emergency if a patient develops acute onset anisocoria.

Old face photographs of patients often help to diagnose and establish the type of anisocoria.

This causes the reversal of anisocoria that is characteristic of Horner's.

At any given eye examination, up to 41% of healthy patients can shown an anisocoria of 0.4 mm or more at one time or another.

Clinically, it is important to establish whether Anisocoria is more apparent in Dim or Bright light:

Anisocoria is usually a benign finding, unaccompanied by other symptoms (physiological anisocoria).

Symptoms that are less common can include limitation of eye movements, other eye problems such as nystagmus or anisocoria, or mild hearing loss.

Alkaloids present in plants of the genera Brugmansia and Datura, such as scopolamine, may also induce anisocoria.

Physiological Anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiologic anisocoria.

Mechanical Anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.

Asymmetric pupil or dyscoria, potential causes of anisocoria, refer to an abnormal shape of the pupil which can happens due to developmental and intrauterine anomalies.

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

The main characteristic that distinguishes physiological anisocoria is an increase of pupil size with lower light or reduced illumination, such that the pupils differ in size between the two eyes.

The presence of physiologic anisocoria has been estimated at 20% of the normal population, so some degree of pupil difference may be expected in at least 1 in 5 clinic patients.

Different than Horner's syndrome, and similar to physiological anisocoria, a patient with damage in the dilatator muscle will show aniscoria on conditions of lower light, where the unaffected pupil will react normally, increasing its size.

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).

A patient with anisocoria (one pupil bigger than the other) whose pupil does not react to light (does not constrict when exposed to bright light) most likely has Adie syndrome - idiopathic degeneration of the ciliary ganglion.

DISCUSSION Horner syndrome-characterized by the constellation of miosis, ptosis, anhidrosis (lack of sweating), enophthalmos, and anisocoria (unequal pupil size)-is present in up to 58% of internal carotid artery dissections [1].

When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be presumed to be on the side of the ptosis.