Differential Diagnosis for Unequal Pupils
Single Most Likely Diagnosis
- Physiological anisocoria: This condition is characterized by a normal, benign variation in pupil size, often less than 1 mm in difference. It is the most common cause of unequal pupils and is usually asymptomatic.
Other Likely Diagnoses
- Iris damage or inflammation: Trauma, infection, or inflammation of the iris can cause unequal pupils due to scarring or damage to the iris sphincter muscle.
- Third cranial nerve palsy: A palsy of the oculomotor nerve can result in a dilated pupil on the affected side due to loss of parasympathetic input.
- Adie's tonic pupil: A condition characterized by a dilated pupil that reacts poorly to light, often due to damage to the ciliary ganglion.
Do Not Miss Diagnoses
- Pupil-involving third cranial nerve palsy due to aneurysm: A third cranial nerve palsy caused by an aneurysm, such as a posterior communicating artery aneurysm, can present with a dilated pupil and is a medical emergency.
- Horner's syndrome due to carotid dissection or stroke: A Horner's syndrome caused by a carotid dissection or stroke can present with a constricted pupil and is a potentially life-threatening condition.
- Pupillary dysfunction due to increased intracranial pressure: Increased intracranial pressure can cause pupillary dysfunction, including unequal pupils, and is a medical emergency.
Rare Diagnoses
- Argyll Robertson pupil: A condition characterized by bilateral small, irregular pupils that constrict in response to near vision but not to light.
- Holmes-Adie syndrome: A rare condition characterized by a tonic pupil and areflexia.
- Sympathetic ophthalmia: A rare, inflammatory condition that can cause unequal pupils due to damage to the sympathetic nervous system.