What are the potential causes and treatments of an oval pupil?

Oval Pupil: Causes and Management

Critical Recognition

An oval pupil is a neurological emergency that typically indicates progressive injury to the oculomotor nerve complex or brainstem, most commonly from serious cerebrovascular disease, and demands immediate neuroimaging and neurosurgical consultation. 1

Primary Causes

Life-Threatening Cerebrovascular Emergencies (Most Common)

• Hypertensive cerebral hemorrhage - accounts for approximately 29% of cases with oval pupils 1
• Ruptured saccular aneurysm - particularly posterior communicating artery aneurysms causing third nerve compression 1, 2
• Epidural hemorrhage - from traumatic brain injury with mass effect 1
• Brainstem strokes - affecting the oculomotor nucleus or fascicle 1
• Bilateral cerebral infarction - with increased intracranial pressure 1

Acute Angle-Closure Crisis

• Mid-dilated, asymmetric, or oval pupil during or immediately following acute angle-closure crisis (AACC) 2, 3
• Associated with markedly elevated intraocular pressure (often >40 mmHg), corneal edema, conjunctival injection, and severe eye pain 2
• The pupil becomes oval due to iris ischemia from extremely high IOP 2

Third Nerve Palsy (Recovering or Progressive)

• Transient oval shape may occur during recovery from complete oculomotor palsy 1
• Pupil-involving third nerve palsy with compressive lesions (aneurysm, tumor, trauma) 2

Traumatic Brain Injury

• Fixed dilated pupils in severe TBI may transition through an oval phase 4
• Can be ipsilateral (66%) or contralateral (9%) to the CT abnormality, or associated with diffuse injury (49%) 4

Clinical Significance and Prognosis

Oval pupils represent a transient, unstable phase in progressive injury to the oculomotor complex and indicate impending herniation or worsening neurological status. 1 This is not a stable finding - it typically evolves toward either complete third nerve palsy with fixed dilated pupil or, less commonly, recovery. 1

Immediate Diagnostic Approach

Distinguish Between Ophthalmologic vs. Neurologic Emergency

First, measure intraocular pressure immediately - if IOP is markedly elevated (>30-40 mmHg) with corneal edema and eye pain, this is AACC requiring immediate medical IOP reduction. 3 If IOP is normal, proceed with neurological evaluation. 2

For Suspected Neurologic Cause

• Obtain emergent CT head without contrast as the initial study to identify hemorrhage, mass effect, or herniation 1
• Follow with MRI brain with and without gadolinium plus MRA or CTA if CT is negative or to better characterize lesions, particularly for suspected aneurysm 2
• Assess for other neurological signs: altered mental status, hemiparesis, cranial nerve deficits, signs of increased intracranial pressure 1
• Check vital signs for Cushing's triad (hypertension, bradycardia, irregular respirations) indicating herniation 2

For Suspected AACC

• Perform gonioscopy (when cornea permits visualization) to confirm angle closure 2, 3
• Examine for mid-dilated pupil, poor or absent pupillary reactivity, corneal edema, shallow anterior chamber, and conjunctival injection 2
• Check the fellow eye - it will typically show similar anatomic predisposition with narrow angles 3

Treatment Algorithm

If Acute Angle-Closure Crisis (Elevated IOP)

Initiate immediate medical therapy to lower IOP, followed by laser peripheral iridotomy within hours once the cornea clears. 3

Acute Medical Management

• Topical beta-blocker (timolol 0.5%) 2, 3
• Topical alpha-2 agonist (brimonidine 0.2%) 2, 3
• Topical or systemic carbonic anhydrase inhibitor (acetazolamide 500mg IV or PO) 2, 3
• Hyperosmotic agent (mannitol 1-2 g/kg IV or oral glycerol) for rapid IOP reduction 2, 3
• Pilocarpine 1-2% only after IOP begins to decrease (ineffective when IOP is markedly elevated due to iris ischemia) 2, 3

Definitive Treatment

• Laser peripheral iridotomy (LPI) as soon as cornea clears sufficiently to visualize iris 2, 3
• Prophylactic LPI in fellow eye due to similar anatomic risk 2, 3
• If LPI cannot be performed due to corneal edema despite medical therapy, consider anterior chamber paracentesis, corneal indentation, or surgical iridectomy 2, 3

If Neurologic Cause (Normal IOP)

Immediate neurosurgical consultation is mandatory. 1 The oval pupil indicates evolving herniation or progressive third nerve compression requiring urgent intervention.

For Suspected Aneurysm (Pupil-Involving Third Nerve Palsy)

• Emergent neurosurgical evaluation with MRA/CTA or catheter angiography if high suspicion persists despite normal noninvasive imaging 2
• Surgical clipping or endovascular coiling of aneurysm 2

For Intracranial Hemorrhage or Mass Effect

• Neurosurgical decompression (craniotomy, hematoma evacuation) as indicated 1
• Medical management of increased ICP (head elevation, hyperventilation, hyperosmolar therapy, sedation) as temporizing measures 1

For Traumatic Brain Injury

• ICP monitoring and management per severe TBI protocols 4
• Surgical evacuation of mass lesions causing herniation 4
• Note: 72% of TBI survivors with fixed dilated pupils have long-term ophthalmologic sequelae 4

Critical Pitfalls to Avoid

• Do not assume the oval pupil localizes to the ipsilateral hemisphere - it can be a false-localizing sign, occurring contralateral to the mass lesion in 9% of cases 4, 1
• Do not delay neuroimaging in patients with oval pupils and normal IOP - this represents evolving neurological deterioration 1
• Do not use pilocarpine in AACC when IOP is extremely elevated - the iris sphincter is ischemic and will not respond, potentially worsening pupillary block 2, 3
• Do not perform only CT without MRI/MRA when aneurysm is suspected - CT may miss small aneurysms 2
• Do not forget to treat the fellow eye prophylactically in AACC - it has an 88-89% risk of developing angle closure if left untreated 2

Post-Acute Management

After AACC Resolution

• Repeat gonioscopy to assess for peripheral anterior synechiae (PAS) and confirm angle opening 3
• Monitor IOP - persistent elevation may indicate trabecular damage, plateau iris syndrome, or need for cataract extraction 3
• Consider lens extraction if significant residual angle closure persists despite patent iridotomy 2, 3

After Neurologic Recovery

• Ophthalmology follow-up for management of residual third nerve palsy, if present 2
• Prism therapy or occlusion for diplopia during recovery phase 2
• Strabismus surgery may be considered after 6 months if no further recovery occurs 2