What is the incidence of ocular ischemic syndrome?

Incidence of Ocular Ischemic Syndrome

Ocular ischemic syndrome is a rare condition with no precise incidence data available in the published literature, though it occurs far less frequently than central retinal artery occlusion (CRAO), which itself has an incidence of only 1.9 per 100,000 person-years in the United States. 1

Epidemiological Context

The incidence of ocular ischemic syndrome (OIS) has not been systematically quantified in population-based studies. However, we can contextualize its rarity by comparing it to related retinal arterial occlusive conditions:

Central Retinal Artery Occlusion (CRAO) Incidence

• United States: 1.9 per 100,000 person-years 1
• South Korea: 1.8 per 100,000 person-years 1
• Japan: 2.5 per 100,000 person-years 1
• Olmsted County, Minnesota: approximately 1 per 100,000 1
• Korea (ages 65-89): 7-10 per 100,000, increasing with age 1

Age-Related Patterns

• Incidence rises dramatically with age, reaching 10.1 per 100,000 person-years in those >80 years of age 1
• Peak incidence occurs near age 80 1
• Men have slightly higher incidence than women 1

Why OIS is Even Rarer Than CRAO

Ocular ischemic syndrome represents a distinct and more severe manifestation of chronic ocular hypoperfusion compared to acute retinal artery occlusion. 2, 3 While CRAO results from acute embolic or thrombotic occlusion of the central retinal artery, OIS develops from chronic, severe stenosis or occlusion of the internal carotid or ophthalmic artery. 2, 3, 4

Key Distinguishing Features

• OIS requires 74% of cases to have 80-99% stenosis or complete occlusion of the ipsilateral internal carotid artery 2
• The condition is progressive and results from chronic hypoperfusion rather than acute occlusion 3, 4
• OIS remains significantly underdiagnosed due to lack of awareness among clinicians 5

Clinical Implications of Rarity

Patient Demographics

When OIS does occur, it affects:

• Mean age of 68 ± 8 years 2
• Predominantly patients with severe systemic atherosclerotic disease 2, 3
• 56% have diabetes mellitus (much higher than general population) 2
• 50% have arterial hypertension 2
• 38% have coronary artery disease 2
• 31% have previous stroke or transient ischemic attack 2

Critical Pitfall to Avoid

Do not confuse OIS with CRAO or other acute retinal arterial occlusions. 1, 6 OIS presents with gradual visual loss (28% of cases) or sudden visual loss (41%), often preceded by amaurosis fugax (15%), and is characterized by chronic ischemic changes including iris neovascularization (87% of cases), rather than the acute cherry-red spot typical of CRAO. 2

Prognostic Significance

• Visual acuity ≤20/400 in 64% of affected eyes at presentation 2
• The condition carries poor visual prognosis but serves as a critical warning sign of severe systemic cardiovascular and cerebrovascular disease 2, 3
• Early diagnosis and prompt carotid revascularization can stabilize or improve vision in 93.3% of cases 5