What is Ocular Ischemic Syndrome?
The ophthalmic artery is the first branch of the carotid artery within the membrane-covered space of the brain. This artery tells us about the blood flow status of the vessel. Ocular Ischemic Syndrome (OIS) is an eye condition that happens due to a narrowing of the carotid artery, which carries blood to the head and neck. Sudden signs of this disease can include brief episodes of insufficient blood flow to the brain and blockage of the retinal artery, while long-term signs include damage to the retina, growth of new blood vessels, and related consequences.
The first case of OIS was reported in 1963 by a person named Hedges, who observed retinal bleeding and vein enlargement in a patient with a totally blocked internal carotid artery, an artery supplying blood to parts of the head. The same year, Kearnst and Hollenhorst gave the condition the name ‘venous stasis retinopathy’ after finding that about 5% of people with blocked or narrowed carotid arteries showed similar eye signs and symptoms. To avoid mixing up this condition with non-ischemic central retinal vein occlusion, which can also cause ‘venous stasis retinopathy’, the term Ocular Ischemic Syndrome (OIS) was introduced by Dr. Gary C Brown and Dr. Larry Magargal. The eyes of people with this disease usually didn’t show signs of inflammation, further distinguishing it from other conditions.
What Causes Ocular Ischemic Syndrome?
The main cause of this disease is atherosclerosis, which is a condition where fatty deposits build up inside the arteries, making them narrower. Other conditions that can also contribute to the disease include a dissecting aneurysm of carotid vessels, which is a tear in the inner lining of the artery, and conditions like Takayasu arteritis, giant cell arteritis, and aortic arch syndrome, which are all types of inflammation in the arteries. Conditions like fibrovascular dysplasia, a condition that causes abnormal growth in the walls of the blood vessels, Behcet’s disease, which causes inflammation throughout the body, and any trauma or inflammation can also lead to narrowing of carotid arteries.
In addition, if someone also has conditions like high blood pressure or diabetes, they should be closely monitored. Statistics show that 73% of people with this disease have high blood pressure, and 56% have diabetes. People with this disease and these conditions have a generally higher risk of heart attack and stroke compared to the rest of the population.
Risk Factors and Frequency for Ocular Ischemic Syndrome
OIS is a rare condition that affects approximately 7.5 out of a million people each year. However, this number might be higher due to late diagnoses and underreporting. It’s twice as common in males and tends to appear in individuals between the ages of 50 to 80, with the average age at diagnosis being 65. About 20% of people with OIS have the condition in both eyes.
Signs and Symptoms of Ocular Ischemic Syndrome
Ocular ischemic syndrome, or OIS, is primarily identified by a gradual loss of vision that occurs over weeks or months. This condition happens in 80% of the patients. Sometimes, vision loss can happen suddenly, often accompanied by a serious eye condition called neovascular glaucoma, and a distinct spot in the retina known as a “cherry-red spot” (seen in 12% of cases). Patients could either have a mild to moderate visual acuity (in 43% of cases) or a severe vision loss where they could only see fingers or worse (in 37% of cases). After a year of being diagnosed, 24% have mild to moderate visual acuity, and 58% continue to see only fingers or worse.
In addition to vision changes, patients may also experience a dull aching pain in or around the eye (40%. This pain, referred to as “ocular angina,” is caused by a lack of blood supply to the eye, increased pressure in the eye or due to lack of blood supply to the brain membranes on the same side. In 12% of the cases, patients could experience temporary blind spots. Some people might also have difficulty seeing when exposed to bright light because of damaged blood vessels in the eye that delay recovery of light-sensitive cells, known as photoreceptors.
OIS also has many physical features that doctors can observe during an examination. These include:
- New blood vessels in the iris (67% of patients)
- Mild inflammation in the front part of the eye
- Tightened or stuck together iris and lens (anterior synechiae) or iris and cornea (posterior synechiae)
- Partially dilated pupil with poor light response due to the weakened muscle controlling the pupil size
- Bleeding within the eye
- Cataract that develops differently in both eyes
- Red and swollen white part of the eyes
- Swollen cornea with distinctive folds (sometimes leading to severe corneal swelling), rarely causing softening of the white part of the eye
- Narrow blood vessels in the retina (90%)
- Widened and non-twisted veins in the retina (90%)
- Bleeding in the retina (80%)
- Small balloon-like bulges in the retina blood vessels (80%)
- Red spots in the retina (12%)
- White cholesterol fragments blocking the blood vessels
- Glaucoma caused by new blood vessels or without increased eye pressure
- New blood vessels growing in the optic disc (35% of patients) or the retina (8% of patients)
- White patches in the retina (6%)
- Bleeding into the jelly-like substance that fills the back of the eye (4%)
- Pulsations in the blood vessels of the retina (4%)
- Disease affecting the optic nerve due to low blood supply (2%)
- New blood vessels growing under the retina
- Areas in the retina and the layer underneath losing their function.
Testing for Ocular Ischemic Syndrome
A fluorescein angiogram is a critical test for diagnosing Ocular Ischemic Syndrome (OIS), an eye condition caused by reduced blood flow. The test involves injecting a dye into your bloodstream and taking pictures as the dye passes through the blood vessels in your eye. The most common sign of OIS found with this test is a delay in ‘choroidal filling’, where the dye takes more than five seconds to reach all the blood vessels in the choroid (layer of blood vessels and connective tissue lying between the retina and the white of the eye). In some severe cases, the delay can be more than 1 minute.
Late arterial staining is also a common sign seen in 85% of cases. This happens when the dye stains the blood vessels in the eye due to damage from reduced blood flow. In some cases, it can look similar to a condition known as frosted branch angiitis on the test images.
In 17% of the cases, the test might also show ‘macular edema’, which is swelling or thickening of the macula- the part of the eye needed for sharp, central vision. Other signs to look for include non-perfusion of retinal capillaries, small bulging pouches in blood vessels called microaneurysms, and unusual brightness of the optic nerve head.
Another test, Indocyanine Green Angiography (ICG), uses a different dye and can more clearly show any abnormalities in the choroid. As with the fluorescein angiogram, increased time for dye to reach the choroid or within it suggest OIS. The test may also show filling defects and blockage in this area.
An Electroretinogram (ERG) is a test that measures the electrical response of light-sensitive cells in your eyes. OIS can cause a decrease in the sizes of the waves in the ERG recording. This decrease can affect both inner and outer layers of the retina.
Visual-evoked Potentials (VEP) is a test that measures the electrical signals to your brain that are caused by visual stimuli. In OIS, the VEP shows delayed and decreased responses after exposure to bright light.
Ophthalmodynamometry is a test used to measure the pressure needed to make the arteries in the eye pulse. The values of this test are usually reduced in OIS patients and may improve after surgery on the carotid artery (main arteries in the neck supplying blood to the brain).
Now, let’s come to the imaging tests used for evaluating the blockage in the carotid arteries, which is the underlying issue in OIS. For instance, Color Doppler Imaging and Carotid Duplex Ultrasound are used to see the vessels behind your eyes and carotid arteries, looking for reversals in blood flow patterns and dampened Doppler effects.
Magnetic Resonance Angiography (MRA) and Computed Tomographic Angiography (CTA) are also highly accurate scans that can detect serious narrowing or complete blockages in your carotid arteries. Carotid arteriography, while once considered the gold standard, is reserved for ambiguous cases due to possible complications and high costs.
Treatment Options for Ocular Ischemic Syndrome
Managing ocular ischemic syndrome (OIS), a condition that affects the blood supply to the eyes, requires a three-part approach featuring ocular treatment, systemic treatment, and, if necessary, surgery. OIS treatment typically involves teams of different specialized doctors working together.
Ocular Treatment:
In OIS, high eye pressure (IOP) is often not responsive to medication. Drugs that slow down the fluid production in your eye, such as beta-blockers and alpha agonists can be utilized. However, medications that could potentially cause inflammation, such as prostaglandin analogs, pilocarpine, and anticholinergics should be avoided. If the doctor can visualize the eye clearly, laser treatment called panretinal photocoagulation might be performed to help control IOP and reduce iris blood vessel growth. In some cases, surgery could be needed to manage the eye pressure or to alleviate pain in a non-seeing eye. In these worst-case scenarios, stronger approaches like removing the eye (enucleation) or taking out the eye contents (evisceration) could be considered.
Eye drops containing steroids can be employed to manage inflammation in the front part of the eye. Other treatments include intravitreal AntiVEGF, an injection into the eye, which can control blood vessel growth and manage macular edema, a condition involving swelling in the center part of the retina.
Systemic Treatment:
Patients with OIS should also be assessed and treated for any associated health problems by a neurologist and a general physician.
Surgical Management:
Surgery could be potentially beneficial for the vision of a patient with OIS, but only before certain complications like neovascularization (growth of new blood vessels) of the iris (NVI) or neovascular glaucoma (NVG) set in, as they indicate irreversible damage.
One surgical treatment option is Carotid Artery Endarterectomy (CEA), a procedure that removes a blockage from the carotid artery. The most notable study on this procedure, the North American Symptomatic Carotid Endarterectomy trial, showed that CEA, combined with aspirin, provides a better chance of preventing stroke compared to aspirin alone in patients with carotid artery blockages, whether they’re experiencing symptoms or not. If the blockage is less severe, aspirin is typically the treatment of choice.
In some cases, another procedure called Carotid Artery Stenting (CAS), can be performed, especially in patients where CEA might have complications. This is a procedure where a tube is placed in the carotid artery to prevent any blockage.
A third surgical option, Bypass Surgery (Extracranial-Intracranial: EC-IC), involves connecting two arteries to bypass a blockage and prevent any damage due to the shortage of blood supply to the brain. This could be useful in cases where the carotid artery blockage can’t be assessed or treated directly.
What else can Ocular Ischemic Syndrome be?
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This health condition needs to be distinguished from two others: central retinal vein occlusion and diabetic retinopathy. Both seem similar but have different characteristics:
In central retinal vein occlusion, the veins in the eye are enlarged and twisty. There are usually flame-shaped bleeds in all areas of the retina. Unlike in diabetes, small bulges in the blood vessels and patches of fat deposit are not common at the back of the eye. There can also be abnormal blood vessels on the optic disk, which is often swollen. Even with these changes, the blood perfusion pressure in the main artery of the eye remains normal. A special eye test using a dye (fundus fluorescein angiography) would show a delay in the passage of blood from the arteries to the veins with staining of veins and pooling of the dye at the center of the retina suggesting swelling.
In people with diabetic retinopathy, the pathologic changes are seen at the back of the eye, with dilated and “beaded” blood vessels. They also have both dot and flame-shaped bleeds, and small bulges in the blood vessels that leak fat deposits. In a fundus fluorescein angiography test, there is no delay in the passage of blood from the arteries to the veins, but there will be leakage from the small bulging blood vessels and swelling. Also, the growth of new blood vessels that can leak can be observed.
What to expect with Ocular Ischemic Syndrome
The survival rate for patients with OIS is 60% over five years. Heart attacks are the cause in 67% of these cases, while strokes account for 19%.
The outlook for maintaining vision is also not very promising. In the year following diagnosis, about half of patients lose enough vision that they can’t see more than a finger count. For patients with NVG, the outlook is even worse—over 80% develop such poor vision within three months.
A study found that how long a patient’s macula (a part of the eye essential for sharp vision) has been starved of blood might indicate how their vision will fare more accurately than their eyesight when they were diagnosed.
Possible Complications When Diagnosed with Ocular Ischemic Syndrome
Eye-related complications can include the development of new blood vessels in the front and back of the eye, which can result in a type of condition called neovascular glaucoma. This is a possible complication that may lead to vision loss. There can also be disruptions to the optic nerve due to lack of blood supply in the front and back of the eye. Other complications may include bleeding within the eye, inability to move the eye, inflammation of the middle layer of the eye, and reduced eye pressure.
Common Eye-Related Complications:
- Development of new blood vessels in the front and back of the eye
- Neovascular glaucoma potentially leading to vision loss
- Disruption to the optic nerve due to lack of blood supply
- Bleeding within the eye
- Inability to move the eye
- Inflammation of the middle layer of the eye (uveitis)
- Reduced eye pressure
Preventing Ocular Ischemic Syndrome
If a patient is diagnosed with OIS, which stands for Ophthalmic Ischemic Syndrome, a condition that can affect vision, they should continuously seek care from eye doctors and general physicians. The reason for this is to spot and manage any possible serious complications that might threaten their life or their eyesight.
