What diagnostic imaging is recommended for suspected retinal artery occlusion or optic nerve compression?

Diagnostic Imaging for Suspected Retinal Artery Occlusion or Optic Nerve Compression

Optical coherence tomography (OCT) is the primary imaging modality for suspected retinal artery occlusion, as it provides immediate, non-invasive confirmation even when fundus signs are absent, while fluorescein angiography serves as the definitive test to document flow patterns and extent of ischemia. 1, 2

Initial Imaging Algorithm for Retinal Artery Occlusion

First-Line Imaging: OCT

• OCT should be performed immediately as it detects paracentral acute middle maculopathy (PAMM), the earliest sign of acute retinal artery occlusion, before other clinical findings appear 1
• OCT reveals increased hyperreflectivity and thickening of inner retinal layers in acute occlusion, followed by inner retinal thinning in chronic cases 1, 2
• This modality is the most confirmative diagnostic method even when fundus examination appears normal 2

Second-Line Imaging: Fluorescein Angiography (FA)

• FA definitively documents arterial flow alterations, including delayed arterial filling, areas of capillary nonperfusion, and the extent of retinal vasculature involvement 1, 3
• Perform FA to demonstrate delayed arteriovenous transit time (>23 seconds indicates significant occlusion) and to identify retrograde filling patterns that may indicate better prognosis 2, 4
• FA distinguishes between arterial and venous occlusions through characteristic filling patterns: arteritis shows delayed arterial filling and arterial wall staining, while phlebitis shows venous wall staining and perivenular hemorrhages 3

Adjunctive Imaging: Indocyanine Green Angiography (ICG)

• ICG angiography is particularly valuable when giant cell arteritis (GCA) is suspected, as it visualizes choroidal circulation better than fluorescein due to deeper tissue penetration 1
• Use ICG when fluorescein angiography is blocked or when evaluating ophthalmic artery occlusion with suspected choroidal involvement 1

Documentation: Color Fundus Photography

• Fundus photography documents vascular caliber changes, retinal emboli characteristics, presence of "boxcarring" (segmental blood column interruption), cotton-wool spots, and retinal hemorrhages 1, 3
• Red-free photography enhances visualization of nerve fiber layer changes and vascular patterns 1

Imaging for Optic Nerve Compression

When Media Opacity Exists

• Ultrasonography is essential when vitreous hemorrhage or other media opacity prevents direct visualization, ruling out retinal detachment and other acute causes of vision loss 1
• B-scan ultrasonography can identify optic nerve head abnormalities and assess anatomic status when OCT cannot penetrate 1

Advanced Neuroimaging

• MRI with diffusion-weighted imaging (DWI) can detect optic nerve ischemia when central retinal artery occlusion extends proximally along the optic nerve 5
• Consider MRI when clinical findings suggest more proximal vascular occlusion or when embolic source is not identified on standard ophthalmologic examination 5

Critical Time-Sensitive Considerations

Do Not Delay Transfer for Imaging

• Ancillary imaging should never delay transfer to a stroke center in cases of acute, non-arteritic retinal artery occlusion, as stroke risk may be as high as 25% 1
• Acute retinal artery occlusions represent an ophthalmic emergency requiring prompt evaluation 1

Giant Cell Arteritis Workup Takes Priority

• In patients over 50 years with acute vision loss, obtain ESR and CRP immediately before any imaging if GCA is suspected based on headache, scalp tenderness, jaw claudication, temporal tenderness, or systemic symptoms 1, 3
• Poor choroidal circulation on FA or ICG is highly suggestive of ophthalmic artery occlusion from GCA 1

Common Pitfalls to Avoid

Fluorescein Angiography Risks

• Obtain informed consent and have emergency protocols in place, as severe complications including death occur in approximately 1 per 200,000 patients 1
• Question women of childbearing age about pregnancy and breastfeeding; fluorescein crosses the placenta, though fetal harm has not been documented 1

OCT Angiography Limitations

• OCT angiography confirms diagnosis by showing disruption of superficial and deep capillary plexuses, but cannot be performed in all cases due to media opacity or patient cooperation 2, 6
• When clear images are obtained (approximately 73% of cases), OCTA provides valuable confirmation of deep capillary ischemia 2

Gonioscopy Cannot Be Omitted

• Perform gonioscopy before dilation when neovascularization of the iris is suspected or intraocular pressure is elevated, as neovascularization can occur up to 4 months after acute arterial occlusion 1, 3