An “eye stroke” is a non-medical term describing a sudden, often painless loss of vision that occurs when blood flow to the retina is blocked. The retina, a light-sensitive tissue at the back of the eye, requires a constant supply of oxygen and nutrients. The formal medical term is a Retinal Artery or Retinal Vein Occlusion. When blood flow is interrupted, retinal cells are deprived of oxygen, leading to rapid damage and potential permanent vision loss.
Understanding Ocular Vascular Occlusion
The physical mechanism of an eye stroke involves a blockage in one of the two main types of retinal blood vessels: arteries or veins. A Retinal Artery Occlusion (RAO) is caused by an obstruction, typically an embolus or clot, within the artery that supplies oxygenated blood to the retina. This blockage immediately halts the oxygen supply, leading to rapid cell death and vision loss (ischemia). RAO is considered the more severe type of eye stroke because the damage can be irreversible within hours.
A Retinal Vein Occlusion (RVO), conversely, occurs when the vein that drains deoxygenated blood away from the retina becomes blocked or compressed. This is often caused by a clot or thickening of the arterial wall where an artery crosses over a vein. The blockage causes blood to back up, leading to high pressure, swelling, and leakage of fluid and blood into the retinal tissue. While RVO can also cause severe vision loss, it typically presents with a more gradual onset of blurry vision compared to the sudden blackout associated with RAO.
Systemic Conditions That Damage Blood Vessels
The underlying causes of both artery and vein occlusions are often chronic systemic diseases that compromise the health of the body’s blood vessels. Hypertension, or high blood pressure, is a primary risk factor. The chronic force of elevated pressure damages the delicate walls of the retinal vessels, causing them to thicken and stiffen. This process narrows the internal diameter, making the vessels susceptible to blockage.
Atherosclerosis, often linked with high cholesterol, involves the buildup of fatty plaques inside the artery walls. This plaque accumulation narrows the arteries throughout the body, including those feeding the eye, and creates rough surfaces where blood clots can form.
Diabetes Mellitus complicates vascular health by damaging the microvasculature, known as diabetic retinopathy. Chronically high blood sugar levels damage the inner lining of blood vessels, increasing the risk for both arterial and venous blockages. Diabetes also contributes to blood viscosity changes and accelerates atherosclerosis, often combining with hypertension to significantly increase stroke risk.
Specific Sources of Emboli and Inflammation
Retinal artery occlusions are often caused by emboli that originate outside the eye and travel through the bloodstream until they become trapped. Carotid artery disease is a frequent source, where atherosclerotic plaques in the large carotid arteries in the neck shed fragments. These emboli then travel up the ophthalmic artery and into the smaller retinal arteries, causing an immediate blockage.
Heart conditions are another major source of emboli that can lead to an eye stroke. Irregular heart rhythms, such as Atrial Fibrillation, can cause blood to pool and clot within the heart chambers. These clots can be pumped out and travel to the eye’s circulation. Issues with heart valves can similarly lead to the formation of emboli that obstruct the retinal artery.
Direct vessel inflammation, known as vasculitis, also causes a specific type of eye stroke. Giant Cell Arteritis (GCA) causes the walls of medium- and large-sized arteries to swell. This swelling mechanically narrows the vessel lumen, leading to ischemia in the optic nerve and retina. GCA-related occlusions require immediate treatment with high-dose steroids to prevent permanent vision loss and protect the other eye.