Ocular Ischemic Syndrome: Protecting Your Vision
Understanding Ocular Ischemic Syndrome
Ocular ischemic syndrome (OIS) develops when chronic, severe narrowing or blockage of the internal carotid artery reduces blood flow to the eye. The ophthalmic artery, which supplies blood to the eye, is the first major branch of the internal carotid artery. When blood flow through the carotid artery is significantly reduced, the eye does not receive enough oxygen and nutrients to function properly.
Blood flow to the eye remains relatively normal until the carotid artery is blocked by roughly more than half (AAO, EyeNet). When the blockage reaches about the vast majority, the blood pressure inside the central retinal artery drops by roughly half (AAO, EyeNet). This severe drop in blood flow triggers the signs and symptoms of ocular ischemic syndrome.
Atherosclerosis, the buildup of fatty deposits inside artery walls, is the primary cause of carotid artery narrowing that leads to OIS. As plaques build up inside the carotid artery, less blood reaches the ophthalmic artery and the retina. The retina is the light-sensitive tissue at the back of the eye that converts light into signals sent to the brain.
When the retina does not receive enough blood, it becomes ischemic, meaning it is starved of oxygen. This oxygen deprivation can damage retinal cells, trigger abnormal blood vessel growth, and lead to progressive vision loss if not treated.
Not everyone with severe carotid artery disease develops ocular ischemic syndrome. The body has backup pathways called collateral circulation that can reroute blood to the eye. Patients with healthy collateral connections between the internal and external carotid arteries may avoid OIS even with a complete blockage of one internal carotid artery. In contrast, patients with poor collateral circulation may develop OIS with relatively modest carotid artery narrowing (AAO, EyeNet).
Who Is Affected and Risk Factors
Ocular ischemic syndrome most commonly affects people between the ages of 50 and 80. The average age of onset is around 65 years. Men are affected about twice as often as women, primarily because cardiovascular disease is more prevalent in men (AAO, EyeNet).
OIS is closely linked to conditions that promote atherosclerosis. Studies have found the following conditions are significantly more common in patients with OIS (Sivalingam et al., 1991):
- Systemic arterial hypertension, present in approximately more than half of OIS patients
- Diabetes mellitus, present in approximately more than half of OIS patients
- Peripheral vascular disease, present in approximately a notable percentage of OIS patients
- Coronary artery disease and history of heart attack
- Previous stroke or transient ischemic attack (mini-stroke)
- History of hemodialysis
Ocular ischemic syndrome is uncommon. The estimated incidence is 7.5 cases per million people per year (AAO, EyeNet). Despite its rarity, OIS carries serious implications. Research has shown that about 5 percent of patients with significant carotid artery occlusion or stenosis develop ocular signs of this condition (AAO, EyeNet).
Signs and Symptoms
Vision loss is the most common symptom of ocular ischemic syndrome. It affects over the vast majority of patients at the time of diagnosis (Sivalingam et al., 1991). The vision loss typically develops gradually over days to weeks, though some patients experience more sudden changes. About a notable percentage of patients have no visual symptoms when the condition is first detected during an eye examination (AAO, EyeNet).
Many patients with OIS report a dull, aching pain over the affected eye and eyebrow. This discomfort, sometimes called ocular angina, is caused by reduced blood flow to the eye and surrounding tissues. Some patients notice that the pain improves when they lie down, because the position change may slightly improve blood flow. Pain may also result from elevated eye pressure caused by neovascular glaucoma (a type of glaucoma triggered by abnormal blood vessel growth).
Patients with OIS may experience several additional visual disturbances:
- Amaurosis fugax, a temporary loss of vision in one eye lasting seconds to minutes, caused by brief interruptions in blood flow
- Prolonged recovery of vision after exposure to bright light, caused by severe swelling in the macula (the central part of the retina)
- Gradual dimming or blurring of vision in one eye
A retina specialist can identify several telltale signs of OIS during a dilated eye exam. The front of the eye may show neovascularization of the iris (abnormal new blood vessels on the colored part of the eye). This finding is present in 60 to 66 percent of OIS cases (AAO, EyeNet). Inflammation inside the eye occurs in 20 to 50 percent of patients (AAO, EyeNet).
The back of the eye often shows the most characteristic findings. These include narrowed retinal arteries, dilated retinal veins, and mid-peripheral retinal hemorrhages (bleeding). Microaneurysms (tiny bulges in blood vessel walls), cotton-wool spots (white patches indicating nerve fiber damage), and macular swelling may also be present. In advanced cases, abnormal new blood vessels may grow on the optic disc or retina.
Diagnosis and Testing
Diagnosis of ocular ischemic syndrome begins with a thorough eye examination by a retina specialist. This includes checking visual acuity, measuring eye pressure, and performing a dilated examination of the retina. The retina specialist will look for the combination of signs described above. The pattern of retinal hemorrhages and blood vessel changes helps distinguish OIS from other retinal vascular conditions.
Several imaging tests help confirm the diagnosis and assess severity. Fluorescein angiography is a test in which a special dye is injected into a vein in the arm. Photographs are taken as the dye travels through the retinal blood vessels. In OIS, this test typically shows delayed filling of the retinal arteries and veins, along with areas of leakage. Optical coherence tomography (OCT) provides detailed cross-sectional images of the retina to detect macular edema (swelling). OCT angiography, a newer non-invasive technique, can reveal decreased retinal vessel density.
Because OIS is caused by carotid artery disease, imaging of the neck arteries is essential. A retina specialist who suspects OIS will refer the patient for carotid artery evaluation. Carotid duplex ultrasound is usually the first test performed. It uses sound waves to create images of the carotid arteries and measure blood flow. CT angiography or MR angiography may be needed to determine the exact degree of narrowing and plan treatment.
Patients diagnosed with OIS need a complete cardiovascular evaluation. A retina specialist will coordinate with the patient's primary care physician and vascular surgery team. This evaluation typically includes assessment of blood pressure, blood sugar, cholesterol, and heart function. OIS signals a high risk of heart attack and stroke.
Treatment Options
The definitive treatment for ocular ischemic syndrome is restoring blood flow through the blocked carotid artery. This is accomplished through carotid endarterectomy (CEA), a surgical procedure to remove plaque from inside the artery, or carotid artery stenting, in which a small mesh tube holds the artery open. Carotid reperfusion surgery can prevent the progression of chronic ocular ischemia and reduce the risk of stroke. A retina specialist who suspects OIS will refer the patient to the appropriate vascular surgery team.
Panretinal photocoagulation (PRP) is a laser treatment applied to the peripheral retina. It is used when abnormal new blood vessels have developed on the iris or retina. The laser reduces the oxygen demand of the retina, which helps decrease signals that drive abnormal blood vessel growth. Research shows that PRP causes regression of iris and angle neovascularization in about 35 percent of treated eyes (AAO, EyeNet). If neovascular glaucoma has caused the drainage angle of the eye to close, PRP should be performed before glaucoma surgery.
Anti-VEGF medications block vascular endothelial growth factor, a protein that drives abnormal blood vessel growth. These drugs can be injected directly into the eye to treat complications of OIS. Avastin (bevacizumab), which is FDA-approved for cancer treatment and used off-label for eye conditions, has been used to treat neovascularization and macular edema caused by OIS. Other anti-VEGF agents such as Eylea (aflibercept), Lucentis (ranibizumab), and Vabysmo (faricimab) may also be considered.
Intravitreal triamcinolone acetonide, a steroid medication, is another option for treating macular edema associated with OIS. However, this approach often requires multiple injections over time.
Treating the systemic conditions that contribute to carotid artery disease is a critical part of managing OIS. This includes controlling high blood pressure, managing diabetes, lowering cholesterol, and addressing other cardiovascular risk factors. These measures are typically coordinated by the patient's primary care physician and cardiologist, working alongside the retina specialist.
What to Expect
The visual outcome in ocular ischemic syndrome depends on the severity at the time of diagnosis and how quickly blood flow is restored. Even with treatment, visual improvement can be limited because the retina may have sustained significant damage from prolonged ischemia. Some patients experience stabilization or modest improvement after carotid surgery and ocular treatment. Others may continue to lose vision despite treatment.
Ocular ischemic syndrome is a marker of serious, widespread vascular disease. Research has shown that the five-year mortality rate among patients with OIS is approximately 40 percent, compared to 11 percent in an age- and sex-matched control group (Sivalingam et al., 1991). The leading cause of death among OIS patients is cardiac disease, accounting for more than half of deaths, while stroke accounts for a notable percentage (Sivalingam et al., 1991). These statistics underscore the importance of aggressive management of cardiovascular risk factors.
Patients with OIS require regular follow-up with both a retina specialist and their primary care team. The retina specialist will monitor the eye for progression, development of complications such as neovascular glaucoma, and response to treatment. Imaging tests such as OCT and fluorescein angiography may be repeated periodically. OCT angiography studies have shown that retinal vessel density can improve after carotid artery reperfusion surgery.
Living With Ocular Ischemic Syndrome
Living with ocular ischemic syndrome involves making changes that support overall cardiovascular health. A heart-healthy diet low in saturated fats, regular physical activity as recommended by a doctor, smoking cessation, and weight management all help slow the progression of atherosclerosis. These lifestyle changes benefit not only the eyes but also the heart and brain.
Patients with OIS often work with several specialists. These may include a retina specialist, a vascular surgeon, a cardiologist, and a primary care physician. Keeping all members of the care team informed is important for coordinated treatment. Patients should bring updated medication lists to every appointment and report any new symptoms promptly.
A diagnosis of ocular ischemic syndrome can be concerning because it affects both vision and overall health. Patients may benefit from low-vision resources if significant vision loss has occurred. Support from family members and community resources can help with daily tasks that become more challenging. Speaking openly with the retina specialist about expectations and concerns is an important part of managing this condition.
When to See a Retina Specialist
Certain symptoms require immediate medical attention. See a retina specialist or go to the emergency room immediately if you experience any of the following:
- Sudden loss of vision in one eye
- A curtain or shadow moving across your field of vision
- Sudden increase in floaters (spots or lines drifting in your vision)
- Flashes of light in one eye
- Temporary vision loss in one eye lasting seconds to minutes
You should request an evaluation by a retina specialist if you have gradual vision loss in one eye. This is especially important if you have known carotid artery disease or cardiovascular risk factors such as high blood pressure, diabetes, high cholesterol, or a history of stroke. A dull ache around one eye that improves when lying down is another reason to seek prompt evaluation. Early detection of ocular ischemic syndrome provides the best opportunity to preserve vision and reduce the risk of stroke and heart attack.
Questions and Answers
OIS most commonly affects one eye, but it can involve both eyes in patients who have significant atherosclerosis in both carotid arteries. When both eyes are affected, the condition is typically worse on the side with greater carotid artery narrowing. A retina specialist will evaluate both eyes and may recommend imaging of both carotid arteries.
Because OIS is caused by atherosclerosis, the same strategies that reduce cardiovascular risk also help lower the risk of developing this condition. Controlling blood pressure, managing diabetes, maintaining healthy cholesterol levels, exercising regularly, and not smoking all reduce plaque buildup in the arteries. Regular medical checkups that include cardiovascular risk assessment are important, particularly for people over age 50.
Ocular ischemic syndrome is a visible sign that the carotid arteries are severely narrowed. Because the same arteries supply blood to the brain, patients with OIS are at high risk for stroke. The five-year mortality rate of approximately a substantial proportion in OIS patients, primarily from heart attack and stroke, demonstrates that this is not just an eye condition (Sivalingam et al., 1991). Treating the underlying carotid artery disease is essential for protecting both vision and life.
Retinal vein occlusion and OIS can appear similar because both involve retinal hemorrhages and dilated veins. However, they have different causes. A retinal vein occlusion is caused by a blockage in the veins draining blood from the retina. OIS is caused by reduced blood flow into the eye from carotid artery disease. Findings on examination and imaging help a retina specialist distinguish between the two. For example, delayed arterial filling on fluorescein angiography and low eye pressure suggest OIS, while high eye pressure is more typical of vein occlusion.
Not all patients with OIS require intravitreal injections. Injections are used when specific complications develop, such as macular edema or neovascularization. The primary treatment goal is restoring blood flow through the carotid artery. A retina specialist will determine whether injections or other treatments are needed based on the findings in your eye. Some patients may require a combination of carotid surgery, laser treatment, and injections.