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ULY CLINIC

21 Septemba 2025, 01:43:54

Anisocoria

Anisocoria is defined as a difference in the diameter of the pupils, typically ranging from 0.5 to 2 mm. A small degree of anisocoria may be a normal physiologic variant, but when accompanied by abnormal light reactions or other neurologic signs, it may indicate ocular or neurologic disease.

Pathophysiology

Pupillary size and reactivity depend on a balance between:

Parasympathetic innervation (via the oculomotor nerve to the sphincter pupillae → constriction)
Sympathetic innervation (via the long ciliary nerves to the dilator pupillae → dilation)

Disruption of either pathway—at the level of the brain, brainstem, peripheral nerves, or eye—can result in anisocoria:

Parasympathetic lesions → impaired constriction, leaving the pupil larger.
Sympathetic lesions → impaired dilation, leaving the pupil smaller.
Structural or pharmacologic causes → direct effect on the iris muscles.

Causes of anisocoria

Category	Examples	Key Features
Physiologic anisocoria	Benign, found in ~2% of population	Stable difference (<1 mm), unchanged in light or dark
Neurologic causes	Horner syndrome, oculomotor (III) nerve palsy, Adie’s tonic pupil	Often associated with ptosis, diplopia, headache, or other deficits
Ophthalmic disease	Acute angle-closure glaucoma, iritis, traumatic mydriasis, synechiae	Pain, redness, blurred vision, irregular pupil
Pharmacologic	Atropine, scopolamine, pilocarpine, organophosphates	History of topical or systemic drug exposure
Structural lesions	Orbital tumor, aneurysm, carotid dissection	Often acute; may present with headache or visual field changes

Clinical Examination

Inspect pupils in both bright and dim light, noting size and symmetry.
Assess reactivity to light (direct and consensual).
Evaluate near response (accommodation).
Examine for associated signs: ptosis, extraocular movement deficits, facial sweating.
Take a history of trauma, drug use, or headache.

Diagnostic approach

Physiologic anisocoria: Small, stable difference; pupils respond normally to light and accommodation.
Pathologic anisocoria:
- Greater in bright light → abnormal pupil is larger (parasympathetic lesion).
- Greater in dim light → abnormal pupil is smaller (sympathetic lesion).

Urgent neuroimaging is indicated if anisocoria is accompanied by headache, oculomotor palsy, or altered mental status.

Clinical significance

May be the first sign of serious neurologic disease, such as:
- Intracranial aneurysm compressing CN III
- Carotid artery dissection causing Horner syndrome
- Uncal herniation in raised intracranial pressure
Benign cases require reassurance, but pathologic anisocoria warrants prompt investigation.

Patient counseling

Explain that mild, stable differences may be normal.
Advise immediate evaluation if anisocoria develops suddenly, is associated with pain, diplopia, or vision loss.

Key points

Not all anisocoria is pathologic—2% of healthy people have stable pupillary inequality.
Context, light response, and associated signs determine its clinical importance.
Early recognition of dangerous causes (e.g., aneurysm, herniation) can be life-saving.

References

Miller NR, Newman NJ, Biousse V, Kerrison JB. Walsh & Hoyt’s Clinical Neuro-Ophthalmology. 6th ed. Lippincott Williams & Wilkins; 2005.
Kline LB, Bajandas FJ. Neuro-Ophthalmology Review Manual. 7th ed. Slack Inc; 2013.
Biousse V, Newman NJ. Neuro-Ophthalmology Illustrated. 2nd ed. Thieme; 2015.