An eye stroke, medically termed a retinal vessel occlusion, is a sudden loss of vision caused by impaired blood flow to the retina, the light-sensitive tissue at the back of the eye. Similar to a stroke in the brain, a blocked vessel starves the tissue of necessary oxygen and nutrients. This disruption causes rapid damage to the nerve cells responsible for sight. Because these nerve cells can die quickly without blood flow, an eye stroke is a serious medical emergency requiring immediate evaluation to prevent severe vision loss.
The Two Types of Ocular Vessel Occlusion
Eye strokes are categorized based on the type of blood vessel blocked: arteries or veins. A blockage in the central retinal artery, which carries oxygenated blood to the retina, is called a Central Retinal Artery Occlusion (CRAO). CRAO is often compared to an ischemic stroke and typically causes sudden, profound, and painless vision loss because the retina is deprived of oxygen.
Conversely, a blockage in the central retinal vein, which carries deoxygenated blood away from the retina, is known as a Central Retinal Vein Occlusion (CRVO). The blocked vein causes blood and fluid to back up, leading to hemorrhaging, swelling, and leakage within the retina. CRVO tends to cause a more gradual onset of blurred or distorted vision compared to the abrupt loss seen with CRAO.
Immediate Physical Causes of Blockage
The direct physical cause of an eye stroke is vessel obstruction, which primarily occurs through two mechanisms: embolism or thrombosis. An embolism involves a fragment of atherosclerotic plaque or a blood clot that breaks off from a larger vessel and travels until it lodges in a smaller retinal artery. This embolic event is the most common cause of CRAO, with debris typically originating from the carotid arteries in the neck or the heart. Cholesterol deposits, known as Hollenhorst plaques, are frequently identified as the cause of these arterial blockages.
Thrombosis describes a blood clot that forms locally within the retinal vessel itself, often due to damage to the vessel wall. This local clotting is a more frequent cause of CRVO, often occurring where a thickened artery compresses the adjacent vein, promoting clot formation at the crossing point. Other, less common direct causes of vessel closure include inflammation of the blood vessel wall, known as vasculitis, or a temporary, severe narrowing of the vessel called vasospasm.
Systemic Conditions That Create Risk
Underlying systemic health problems are the main drivers that increase the likelihood of the physical blockages causing eye strokes.
Atherosclerosis
Atherosclerosis, the hardening and narrowing of arteries due to fatty plaque buildup, creates a prime environment for embolism. Plaque deposits within the carotid arteries can become unstable, causing fragments to shear off and travel to the smaller retinal arteries, resulting in CRAO. This progressive disease diminishes the integrity of the vascular system, placing the delicate retinal circulation at risk.
Chronic Hypertension
Chronic hypertension, or high blood pressure, damages retinal vessel walls through persistently elevated force. The sustained pressure causes the small arteries in the retina to thicken and narrow, which promotes local clotting (thrombosis) and makes the vessels more susceptible to blockage. Hypertension is a major risk factor for both retinal artery and vein occlusions because it impairs the normal function of the vessel lining. Damage from high blood pressure can also be observed as arteriolar narrowing and arteriovenous nicking in the retina.
Diabetes Mellitus
Diabetes Mellitus significantly accelerates vascular damage throughout the body, including the small vessels of the retina. High blood sugar levels injure the walls of these tiny vessels, increasing the risk of clotting and leakage. This microvascular damage impairs blood flow and fosters insufficient oxygen supply, increasing the chance of retinal vessel occlusion. The presence of diabetic retinopathy, a condition where damaged vessels leak fluid or grow fragile new vessels, is a sign of severe underlying vascular compromise.
Cardiac Disease and Other Factors
Cardiac disease, particularly the irregular heart rhythm known as Atrial Fibrillation (AFib), is a major source of embolic material. AFib causes blood to pool in the upper chambers of the heart, which can lead to the formation of blood clots. These clots can then be pumped out and travel through the bloodstream, where they can ultimately lodge in the central retinal artery and cause a CRAO. Other contributing factors include high cholesterol, which fuels plaque formation, and blood clotting disorders.