Differential Diagnosis for Large Pupils

Single Most Likely Diagnosis

• Benign Physiologic Anisocoria: This condition is characterized by a small, normal variation in pupil size between the two eyes, often noticed in certain lighting conditions. It's a common and harmless condition.

Other Likely Diagnoses

• Pupil Dilation due to Medications: Certain medications, such as anticholinergics, sympathomimetics, and some anesthetics, can cause pupil dilation.
• Traumatic Mydriasis: Trauma to the eye can result in pupil dilation due to iris sphincter damage or third cranial nerve palsy.
• Adie's Pupil (Tonic Pupil): A condition characterized by a dilated pupil that reacts poorly to light, often associated with diminished or absent deep tendon reflexes.

Do Not Miss Diagnoses

• Third Cranial Nerve (Oculomotor Nerve) Palsy: This can be caused by an aneurysm, particularly a posterior communicating artery aneurysm, which is a medical emergency.
• Pupillary Dysfunction due to Increased Intracranial Pressure: Conditions like brain tumors or intracranial hemorrhage can cause pupillary dilation due to compression of the third cranial nerve.
• Ocular Sympathetic Dysfunction (Horner's Syndrome): Although typically associated with miosis (small pupil), in the acute phase, it can present with a dilated pupil on the affected side due to disruption of the sympathetic pathway.

Rare Diagnoses

• Autonomic Dysfunction: Certain rare autonomic disorders can affect pupil size, such as dysautonomia.
• Neurosyphilis: A rare condition that can cause a range of neurological symptoms, including pupillary abnormalities.
• Congenital Conditions: Such as congenital mydriasis or conditions affecting the iris and pupil development.