What is the differential diagnosis for Ocular Ischemic Syndrome (OIS)?

Differential Diagnosis of Ocular Ischemic Syndrome

The differential diagnosis of Ocular Ischemic Syndrome (OIS) primarily includes diabetic retinopathy and central retinal vein occlusion (CRVO), with additional considerations for central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), and other retinal vascular disorders. 1, 2

Primary Differential Diagnoses

Diabetic Retinopathy

• Most commonly confused with OIS due to overlapping features including mid-peripheral retinal hemorrhages, microaneurysms, and neovascularization 1, 2
• Key distinguishing features in OIS: asymmetric presentation, narrowed retinal arteries, marked retinal circulatory stasis, and perifoveal telangiectasias 2
• Diabetic retinopathy typically presents bilaterally with more symmetric findings, whereas OIS is usually unilateral 2
• Fluorescein angiography shows prolonged arteriovenous transit time and delayed choroidal filling in OIS, which differs from diabetic retinopathy 1, 2

Central Retinal Vein Occlusion (CRVO)

• Second most common condition mimicking OIS, particularly moderate CRVO 1, 3
• Both conditions present with dilated retinal veins, retinal hemorrhages, and neovascularization 4, 2
• Critical distinction: CRVO shows dilated and tortuous veins throughout, while OIS demonstrates narrowed retinal arteries with variable venous caliber 2
• CRVO lacks the characteristic arterial narrowing and prolonged arterial filling time seen on fluorescein angiography in OIS 1
• Intraocular pressure in CRVO is typically normal or elevated, whereas OIS can present with hypotony or variable pressures (4-60 mmHg) 2

Secondary Differential Diagnoses

Central Retinal Artery Occlusion (CRAO)

• Presents with sudden, painless vision loss similar to acute OIS presentations 4
• CRAO shows cherry-red spot with retinal whitening in acute phase, which can also occur in OIS 4, 2
• Key difference: CRAO is an acute embolic event, while OIS represents chronic hypoperfusion from carotid stenosis 4, 1
• CRAO typically lacks the anterior segment neovascularization commonly seen in OIS (87% of OIS cases) 2

Branch Retinal Artery Occlusion (BRAO)

• Can present with sectoral vision loss and localized retinal whitening 4
• Distinguished from OIS by sectoral rather than diffuse retinal changes 4
• BRAO patients lack the widespread retinal circulatory stasis and anterior segment neovascularization characteristic of OIS 4, 2

Ophthalmic Artery Occlusion (OAO)

• Represents more severe ischemia affecting both retinal and choroidal circulations 4, 5, 6
• Both OAO and OIS can present with profound vision loss and optic disc changes 4, 2
• OAO shows both retinal and choroidal nonperfusion on fluorescein angiography with dark ring around optic nerve, whereas OIS shows primarily delayed arterial filling 4
• OAO is typically acute and complete, while OIS develops chronically with progressive symptoms 4, 1

Additional Considerations

Giant Cell Arteritis (GCA)

• Must be considered in patients over 50 years presenting with arterial occlusions 4
• GCA presents with systemic symptoms (headache, jaw claudication, temporal artery tenderness) typically absent in atherosclerotic OIS 4
• Requires immediate ESR and C-reactive protein testing, with urgent corticosteroid therapy if suspected 4

Inflammatory Conditions

• Posterior scleritis can present with serous retinal detachment and choroidal folds 4
• Vogt-Koyanagi-Harada disease shows bilateral involvement with vitritis and optic disc edema 4
• These conditions lack the characteristic arterial narrowing and carotid stenosis of OIS 4, 1

Critical Diagnostic Approach

When OIS is suspected, immediately obtain:

• Carotid artery imaging (duplex ultrasonography or CT angiography) to identify internal carotid artery stenosis (≥80%) or occlusion, present in 74% of OIS cases 2, 7
• Fundus fluorescein angiography showing prolonged arteriovenous transit time, delayed choroidal filling, and arterial narrowing 1, 2
• Assessment for systemic vascular disease: diabetes (56% of OIS patients), hypertension (50%), coronary artery disease (38%), and cerebrovascular disease (31%) 2

Common Pitfalls

• Misdiagnosing OIS as diabetic retinopathy in diabetic patients—always consider carotid disease when findings are asymmetric or unilateral 1, 2
• Overlooking the systemic implications—OIS may be the presenting sign of life-threatening cerebrovascular and cardiac disease requiring urgent multidisciplinary evaluation 2, 7, 8
• Failing to recognize that OIS can be asymptomatic with isolated findings like optic disc neovascularization, necessitating high index of suspicion 8
• Delaying carotid imaging—early diagnosis and prompt revascularization (CEA or CAS) can stabilize or improve vision in 93.3% of cases 7