Distinguishing Retinal Arteritis from Retinal Phlebitis on Slit Lamp Examination
Retinal arteritis and phlebitis cannot be reliably distinguished by slit lamp examination alone; fluorescein angiography is required for definitive differentiation. 1
Clinical Findings on Slit Lamp Biomicroscopy
While slit lamp examination with dilated fundus evaluation provides important clues, these findings are suggestive but not definitive:
Features Suggesting Arteritis:
- Arterial narrowing or "boxcarring" (segmental interruption of the blood column within arterioles) 1
- Retinal emboli visible within arterioles 1
- Cotton-wool spots indicating focal ischemia 1
- Relative afferent pupillary defect (RAPD), which signals significant ischemia 1
Features Suggesting Phlebitis:
- Venous tortuosity and dilation 1
- Perivenular hemorrhages distributed along venous pathways 1
- Irregular venous caliber with dilated segments 1
Critical limitation: These clinical findings overlap significantly, and slit lamp examination alone cannot definitively distinguish between the two conditions. 1
Why Fluorescein Angiography is Essential
Fluorescein angiography is the confirmatory diagnostic test that definitively distinguishes arteritis from phlebitis. 1
Arteritis-Specific Angiographic Findings:
- Delayed arterial filling in early phases 1
- Arterial wall staining 1
- Segmental arterial occlusion 1
- Areas of capillary nonperfusion 1
Phlebitis-Specific Angiographic Findings:
- Venous wall staining 1
- Delayed venous drainage 1
- Venous beading patterns 1
- Cystoid macular edema (more common in phlebitis) 1
Critical Clinical Context: Giant Cell Arteritis
If the patient is over 50 years old with suspected arteritis, immediately obtain ESR and CRP before any imaging, as giant cell arteritis requires urgent high-dose corticosteroids. 1
Red Flags Requiring Immediate Workup:
- Age >50 years with acute vision loss 1
- Headache 1
- Scalp tenderness 1
- Jaw claudication 1
- Non-embolic branch retinal artery occlusion in elderly patients 2
Do not delay treatment waiting for temporal artery biopsy if clinical suspicion is high. 1
Recommended Diagnostic Algorithm
Step 1: Slit Lamp Biomicroscopy
Perform dilated fundus examination documenting vascular caliber changes, hemorrhage patterns, and cotton-wool spots. 1 Check for RAPD, which indicates significant ischemia. 1
Step 2: Fluorescein Angiography
This is mandatory for definitive diagnosis and cannot be skipped if you need to distinguish arteritis from phlebitis. 1, 3 Indocyanine green angiography can be added for additional vascular detail. 3
Step 3: Adjunctive Imaging
- OCT detects macular edema (common in phlebitis) and shows inner retinal thickening/hyperreflectivity in acute arterial occlusion 1
- Fundus photography documents vascular sheathing patterns and tracks disease progression 1
- OCT angiography can detect vascular anomalies without contrast 4
Step 4: Gonioscopy
Do not forget gonioscopy, as neovascularization of the iris or angle can occur with severe ischemia from either arteritis or phlebitis. 1
Common Pitfalls to Avoid
Pitfall #1: Assuming clinical examination alone is sufficient. The literature demonstrates that even experienced clinicians cannot reliably distinguish these conditions without angiography. 1, 5
Pitfall #2: Delaying corticosteroids in suspected giant cell arteritis while waiting for confirmatory tests. In patients over 50 with appropriate symptoms, start treatment immediately after obtaining ESR/CRP. 1
Pitfall #3: Ordering extensive laboratory workups in young patients with isolated retinal vasculitis and negative review of systems. Studies show this yields false-positive results in 20.8% of cases without identifying underlying disease. 6
Pitfall #4: Missing the diagnosis of giant cell arteritis when it presents atypically as isolated branch retinal artery occlusion, particularly in elderly patients. 2