What Is Uncal Herniation (Vision)?

Why it affects the eyes and vision

Compression of the third cranial nerve disrupts parasympathetic control of the pupil, which can produce a large, poorly reactive pupil. Eye movement abnormalities may follow as the nerve becomes more compromised. If the posterior cerebral artery is compressed, reduced blood flow to the occipital lobe can cause contralateral homonymous hemianopia. These findings often occur alongside declining consciousness and other signs of raised intracranial pressure.

Warning signs

Symptoms can escalate quickly and may include severe headache, vomiting, confusion, and rapid neurologic decline. Eye findings are a critical clue but do not occur in isolation in most cases.

• New unilateral fixed dilated pupil
• Ptosis or abnormal eye position
• Sudden decreased alertness or coma
• New weakness, abnormal breathing, or seizures

How it is diagnosed

Diagnosis is clinical suspicion plus urgent neuroimaging, typically computed tomography of the head for rapid assessment. Imaging looks for a mass effect, midline shift, and signs of transtentorial herniation. Clinicians also assess pupil responses, eye movements, and other neurologic findings repeatedly to track progression. This is managed in emergency or critical care settings.

Emergency treatment

Treatment focuses on relieving intracranial pressure and addressing the underlying cause, such as hemorrhage, tumor, or swelling. Measures may include airway and ventilation support, hyperosmolar therapy, and urgent neurosurgical intervention when indicated. Time is critical because ongoing compression can cause irreversible brain injury. Do not attempt home management if uncal herniation is suspected.