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

Oval Pupil: Causes and Management

An oval pupil is a critical warning sign of serious intracranial pathology requiring immediate neuroimaging and neurosurgical evaluation, most commonly representing a transient phase of progressive oculomotor nerve injury from cerebrovascular catastrophe or increased intracranial pressure.

Primary Causes

Acute Angle-Closure Crisis (AACC)

• An oval pupil during or following AACC represents one of the cardinal signs of this ophthalmologic emergency 1
• The pupil is typically mid-dilated, asymmetric, or oval-shaped in the involved eye during the acute attack 1
• Pupillary reactivity is poor during AACC or may become nonreactive following the episode 1
• Associated findings include corneal edema, conjunctival hyperemia, markedly elevated IOP, and anterior chamber inflammation 1

Serious Cerebrovascular Disease

• Oval pupils most commonly indicate severe intracranial pathology, with 16 of 17 patients in one series having serious cerebrovascular illness 2
• Specific etiologies include:
  • Hypertensive cerebral hemorrhage 2
  • Ruptured saccular aneurysm 2
  • Epidural hemorrhage 2
  • Bilateral cerebral infarction 2
  • Brainstem strokes 2
• Oval pupils usually represent a transient, unstable phase in progressive injury to the oculomotor complex 2
• Less frequently, they may represent a transient phase of recovery from oculomotor palsy 2

Third Nerve Palsy

• Pupil-involving third nerve palsy can present with irregular or oval pupil shape 1
• A compressive lesion, especially posterior communicating artery aneurysm, must be ruled out urgently 1
• The pupil may be mid-dilated with poor or absent reactivity 1

Traumatic Brain Injury

• Pupillary abnormalities including oval configuration are commonly seen with severe TBI 3
• In patients with unilateral fixed dilated pupils from TBI, 72% of survivors had long-term ophthalmological deficits 3
• A fixed dilated pupil is a grave prognostic sign following TBI 3

Diagnostic Approach

Immediate Assessment

• Measure IOP immediately in both eyes using Goldmann applanation tonometry to rule out AACC 1, 4
• Perform gonioscopy if AACC is suspected (once cornea permits visualization) 1, 4
• Assess pupil size, shape, symmetry, and reactivity to light 1
• Check for relative afferent pupillary defect 1

Slit-Lamp Examination for AACC

• Look for conjunctival hyperemia, corneal edema (microcystic and stromal), and shallow anterior chamber 1
• Examine for iris abnormalities including diffuse or focal atrophy, posterior synechiae, and abnormal pupillary function 1
• Assess for glaukomflecken (patchy anterior subcapsular lens opacities) 1

Neuroimaging for Non-AACC Cases

• Obtain urgent MRI with gadolinium and MRA or CTA if pupil-involving third nerve palsy is suspected 1
• If high suspicion for aneurysm despite normal MRA/CTA, consider catheter angiography 1
• CT imaging may be complementary for detecting hemorrhage, bone involvement, or calcification 5

Treatment Based on Etiology

For Acute Angle-Closure Crisis

Immediate medical therapy followed by laser peripheral iridotomy (LPI) within hours is the standard of care 1, 4:

1. Acute IOP-lowering medications 1, 4:

   • Topical beta-blockers (timolol 0.5%) 1, 4
   • Topical alpha-2 agonists (brimonidine 0.2%) 1, 4
   • Topical or systemic carbonic anhydrase inhibitors 1, 4
   • Topical miotics (pilocarpine 1-2% once IOP begins decreasing) 1, 4
   • Oral or IV hyperosmotic agents (mannitol 1-2 g/kg IV or oral glycerol) for rapid IOP reduction 1, 4

2. Definitive laser peripheral iridotomy as soon as cornea clears 1, 4

   • LPI relieves pupillary block and eliminates pressure gradient between chambers 1, 4
   • Perform in superior iris to avoid visual symptoms 4
   • Confirm patency by visualizing lens structures through iridotomy 4

3. Prophylactic LPI in fellow eye 1, 4

   • The contralateral eye has similar anatomic predisposition 4

For Third Nerve Palsy

• Urgent neurosurgical consultation if compressive lesion identified 1
• Management directed at underlying cause (aneurysm, tumor, trauma) 1
• Temporary diplopia management with prisms or occlusion while awaiting recovery 1

For Cerebrovascular Disease

• Immediate neurosurgical evaluation for hemorrhagic lesions 2
• Stroke protocol management for ischemic events 5
• Secondary stroke prevention measures 5

Critical Pitfalls to Avoid

• Never dismiss an oval pupil as benign without excluding AACC or serious intracranial pathology 1, 2
• Do not delay LPI in AACC waiting for complete corneal clearing—topical hyperosmotic agents or paracentesis can facilitate the procedure 1, 4
• Avoid using miotics when IOP is markedly elevated, as pressure-induced ischemia renders the sphincter unresponsive 1
• Do not assume unilateral fixed dilated pupil localizes ipsilaterally—it can be a false-localizing sign 6
• In traumatic cases, recognize that oval pupils indicate severe injury with poor prognosis but favorable outcomes remain possible 3

Post-Treatment Monitoring

• Repeat gonioscopy after LPI to confirm angle opening 4
• Monitor for persistent IOP elevation suggesting trabecular damage, plateau iris syndrome, or non-pupillary block mechanisms 4
• Regular visual field testing if neurological etiology 5
• Repeat neuroimaging if new symptoms develop 5