Anisocoria which is greater in bright light suggests the larger pupil (which should constrict in bright conditions) is the abnormal pupil.If the smaller pupil dilates in response to instillation of apraclonidine eye drops, this suggests Horner's syndrome is present. In Horner's syndrome sympathetic nerve fibers have a defect, therefore the pupil of the involved eye will not dilate in darkness. 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.Ĭauses of anisocoria range from benign (normal) to life-threatening conditions.Ĭlinically, 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. Alkaloids present in plants of the genera Brugmansia and Datura, such as scopolamine, may also induce anisocoria.

Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines. Pharmacological agents with anticholinergic or sympathomimetic properties will cause anisocoria, particularly if instilled in one eye.In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved.

Oculomotor nerve palsy: Ischemia, intracranial aneurysm, demyelinating diseases (e.g., multiple sclerosis), head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults.

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. It may be associated with loss of deep tendon reflex (Adie's syndrome).

Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women.

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

In this condition, the difference between pupils is usually less than 1 mm.

Physiological anisocoria: About 20% of population has a slight difference in pupil size which is known as physiological anisocoria.

Affecting up to 20% of the population, anisocoria is often entirely harmless, but can be a sign of more serious medical problems.Īnisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes. ə, ˌ æ n aɪ-/ Īnisocoria is a condition characterized by an unequal size of the eyes' pupils.

Cranial nerves for pupil measurement