Can retinal arteritis be reliably distinguished from retinal phlebitis (inflammation of the vein) on slit lamp examination?

Distinguishing Retinal Arteritis from Phlebitis on Slit Lamp Examination

No, you cannot reliably distinguish retinal arteritis from phlebitis on slit lamp examination alone—fluorescein angiography is required for definitive differentiation. 1

Clinical Examination Limitations

While slit-lamp biomicroscopy with appropriate lenses allows visualization of retinal vessels, the clinical findings overlap significantly between arteritis and phlebitis, making definitive distinction unreliable without angiography. 1

What You Can Observe on Slit Lamp

Findings suggestive of arteritis:

• Cotton-wool spots indicating focal ischemia 1
• Arterial narrowing or "boxcarring" (segmental blood column interruption) 2
• Retinal emboli within arterioles 2
• Peripapillary or retinal hemorrhages (though less common than in phlebitis) 3

Findings suggestive of phlebitis:

• Perivenular hemorrhages (more prominent and extensive) 1
• Irregular venous caliber with dilated segments 1
• Venous tortuosity and dilation 2
• More extensive intraretinal hemorrhages 4

Common to both:

• Vascular sheathing (can affect arteries or veins) 1, 3
• Retinal edema 4
• Vitreous inflammation 5

Why Fluorescein Angiography is Essential

Fluorescein angiography provides the definitive diagnostic distinction by revealing dynamic vascular flow patterns that cannot be appreciated on clinical examination alone. 1

Arteritis-specific angiographic findings:

• Delayed arterial filling in early phases 1
• Arterial wall staining 1
• Segmental arterial occlusion 1
• Areas of capillary nonperfusion 2

Phlebitis-specific angiographic findings:

• Venous wall staining (late-phase leakage) 1
• Delayed venous drainage 2
• Venous beading patterns 2
• Cystoid macular edema (more common) 2

Critical Clinical Context: Giant Cell Arteritis

If you suspect arteritis in a patient over 50 years old, immediately obtain ESR and CRP before any imaging, as giant cell arteritis requires urgent high-dose corticosteroids before temporal artery biopsy. 1 This is a medical emergency where hours matter for preventing bilateral blindness. 2

Red flags requiring immediate workup:

• Age >50 years with acute vision loss 2
• Headache, scalp tenderness, or jaw claudication 2
• Cotton-wool spots with arterial narrowing 1
• Relative afferent pupillary defect 2

Practical Diagnostic Algorithm

Step 1: Perform slit-lamp biomicroscopy with dilated fundus examination 2

• Document vascular caliber changes, hemorrhage patterns, and cotton-wool spots 2
• Assess for anterior chamber or vitreous inflammation 5

Step 2: If vasculitis is suspected, obtain fluorescein angiography (and consider ICG angiography for choroidal involvement) 1, 6

• This definitively distinguishes arteritis from phlebitis 1
• ICG may be superior for detecting choroidal hypoperfusion in giant cell arteritis 6

Step 3: Use OCT as adjunctive imaging 1

• Detects macular edema (more common in phlebitis) 1
• Shows inner retinal thickening and hyperreflectivity in acute arterial occlusion 1
• Documents vitreoretinal interface changes 2

Step 4: Obtain fundus photography for documentation 1

• Tracks vascular sheathing patterns and caliber changes over time 1
• Documents hemorrhage distribution and disease progression 1

Key Distinguishing Research Findings

A 2020 study of 283 uveitis patients found that arterial involvement (arteritis 57.9%, inflammatory artery sheathing 33.7%, artery occlusion 22.1%) strongly suggests infectious etiology, while isolated phlebitis is more common in non-infectious inflammatory conditions. 3 This has important treatment implications, as infectious causes require antimicrobial therapy while non-infectious causes require immunosuppression.

Common Pitfalls to Avoid

• Don't rely on vascular sheathing alone—it occurs in both arteritis and phlebitis and cannot distinguish between them 3
• Don't assume bilateral involvement excludes arteritis—giant cell arteritis can be bilateral 2
• Don't delay angiography for "better clinical characterization"—the clinical exam cannot provide the information angiography reveals 1
• Don't forget gonioscopy—neovascularization of the iris or angle can occur with severe ischemia from either arteritis or phlebitis 2

When Angiography is Unavailable

If fluorescein angiography is not immediately accessible and you must make treatment decisions, err on the side of treating for arteritis if the patient has risk factors for giant cell arteritis or infectious causes, as these have higher morbidity and mortality. 1 However, arrange urgent transfer to a facility with angiography capabilities, as definitive diagnosis requires this imaging. 1