How do you diagnose and manage a patient with sudden, painless vision loss to rule out central retinal artery occlusion?

Ruling Out Central Retinal Artery Occlusion

To rule out CRAO, perform immediate funduscopic examination looking for the classic triad: retinal whitening, cherry red spot at the fovea, and boxcar segmentation of blood flow in retinal vessels—if these findings are absent and the patient has normal fundus appearance with normal retinal perfusion, CRAO is effectively ruled out. 1

Key Diagnostic Features to Confirm or Exclude CRAO

Clinical Presentation That Suggests CRAO

• Sudden, painless monocular vision loss occurring over seconds, with visual acuity of "count fingers" or worse in over 80% of cases 1, 2
• Presence of an ipsilateral relative afferent pupillary defect (unless contralateral optic neuropathy exists) 1
• Impaired color vision proportional to the degree of visual acuity loss 1

Funduscopic Examination Findings

Classic findings that confirm CRAO:

• Diffuse retinal whitening from opacification of swollen, ischemic parafoveal nerve fiber layers 1
• Cherry red spot at the foveal center (the normally perfused choroid appears red against the ischemic nerve fiber layer background) 1
• Boxcar segmentation of blood flow in retinal arterioles and veins, best visualized with slit-lamp biomicroscopy 1
• Attenuated retinal arteries with slow, segmental blood flow 1

Findings that help rule out CRAO:

• Normal retinal appearance without whitening or edema 1
• Absence of cherry red spot 1
• Normal caliber and flow in retinal vessels 1
• Presence of intraretinal hemorrhages and dilated, tortuous veins (suggests retinal vein occlusion instead) 1

Timing Considerations for Examination

• The classic appearance may be absent or very subtle in the early stages (first few hours), depending on timing of examination relative to onset 1
• Within several hours, the classic appearance of retinal whitening with cherry red spot becomes typical 1
• Deep retinal whitening from paracentral acute middle maculopathy (PAMM) with inner nuclear layer hyper-reflectivity may be noted initially before progression to complete CRAO 1

Important Diagnostic Caveats

Cilioretinal Artery Sparing

• Approximately 15-25% of eyes have a cilioretinal artery that perfuses part of the macula, which can spare central vision 1
• These patients may have nearly normal visual acuity despite CRAO, making diagnosis more challenging 1
• Visual acuity improvement occurs in 67% of NA-CRAO cases with cilioretinal artery sparing 3

Giant Cell Arteritis Must Be Excluded

• In patients over 50 years of age, arteritic CRAO from giant cell arteritis (GCA) must be ruled out immediately 4, 2
• Obtain ESR and CRP urgently in all patients over 50 2, 5
• GCA-induced CRAO may have coexistent arteritic anterior ischemic optic neuropathy (AION) and choroidal ischemia 1
• If GCA is diagnosed or highly suspected, initiate immediate high-dose systemic corticosteroids (typically IV methylprednisolone 1g daily for 3 days) to prevent vision loss in the contralateral eye 2

Concurrent Stroke Evaluation

• 19-25% of CRAO patients have concurrent silent brain infarctions on brain MRI with diffusion-weighted imaging 2
• Up to 24% have concurrent cerebrovascular accident on diffusion-weighted MRI 2
• Brain MRI with diffusion-weighted imaging and vascular imaging should be performed to assess for concurrent stroke and carotid artery disease 2, 5
• Up to 70% have clinically significant carotid stenosis, with 71% having ipsilateral carotid plaque 1, 2

Time-Critical Actions if CRAO is Confirmed

If funduscopic examination confirms CRAO, immediate transfer to a stroke center or emergency department is mandatory without delay for further outpatient evaluation, as CRAO is an ocular stroke requiring emergent evaluation within 4.5 hours for potential thrombolysis 4, 2