Differential Diagnosis for Dilated Unreactive Pupil
- Single Most Likely Diagnosis
- Oculomotor Nerve (Third Cranial Nerve) Palsy: This condition often presents with a dilated pupil that is unreactive to light, along with ptosis (drooping eyelid) and outward deviation of the eye. The third cranial nerve controls several muscles involved in eye movement and the constriction of the pupil, making its palsy a common cause of a dilated, unreactive pupil.
- Other Likely Diagnoses
- Traumatic Iris Damage: Trauma to the eye can cause damage to the iris, leading to a fixed, dilated pupil. This could be due to direct injury to the iris sphincter muscle or other structures within the eye.
- Adie's Pupil (Tonic Pupil): Characterized by a dilated pupil that reacts poorly to light but has a more pronounced reaction to near vision (accommodation). It's often associated with diminished or absent deep tendon reflexes.
- Pharmacologic Mydriasis: Certain medications or substances (e.g., anticholinergics, sympathomimetics) can cause pupil dilation that may not react to light.
- Do Not Miss Diagnoses
- Acute Angle-Closure Glaucoma: A medical emergency where increased intraocular pressure causes a dilated, often painful, red eye with decreased vision. The pupil may be mid-dilated and unreactive. Prompt treatment is necessary to prevent permanent vision loss.
- Pupillary Involvement in Stroke or Intracranial Hemorrhage: Certain types of stroke or intracranial hemorrhage can affect the brainstem or other areas controlling pupil function, leading to anisocoria (unequal pupil sizes) or a dilated, unreactive pupil.
- Rare Diagnoses
- Syphilis (Argyll Robertson Pupil): A condition where pupils are bilaterally small and irregular, reacting to near vision but not to light. Though classically described in the context of syphilis, this presentation is rare and usually associated with other neurosyphilis symptoms.
- Holmes-Adie Syndrome with Areflexia: While Adie's pupil is more common, the full syndrome including areflexia (absent reflexes) is less frequent and may present with a dilated pupil among other symptoms.