A sudden change in vision can be alarming. The phrase “blood clot in the eye” describes Retinal Vein Occlusion (RVO), a serious medical event where blood flow from the eye is blocked. This blockage causes leakage and subsequent vision loss. RVO is one of the most common causes of vision impairment linked to vascular issues in the retina. Although localized to the eye, RVO often signals broader health issues, making prompt evaluation and treatment by an eye care professional necessary.
Understanding Retinal Vein Occlusion (RVO)
The retina relies on a constant flow of blood to function properly. Retinal arteries deliver oxygenated blood, and retinal veins carry deoxygenated blood away. RVO occurs when a thrombus, or blood clot, obstructs a vein, preventing blood from draining. This blockage causes pressure to build up, leading to blood and fluid leaking into the surrounding retinal tissue.
The location of the occlusion determines the type and severity of RVO. Central Retinal Vein Occlusion (CRVO) involves the main retinal vein. This type typically causes more widespread damage and profound vision loss. Branch Retinal Vein Occlusion (BRVO) is more common and occurs when a smaller tributary vein is blocked. BRVO usually affects a smaller section of the retina, often resulting in less severe vision impairment compared to CRVO.
Systemic Conditions That Cause RVO
The formation of a retinal vein clot is usually a manifestation of underlying systemic health problems affecting the entire vascular system. The most frequent cause of RVO is the stiffening and narrowing of the adjacent retinal artery, known as atherosclerosis, often driven by high blood pressure. Because the retinal artery and vein often share a common sheath, the hardened artery can compress the soft vein where they cross, damaging the vein wall and triggering clot formation.
Chronic high blood pressure (systemic hypertension) is the primary risk factor because it accelerates atherosclerosis throughout the body. Diabetes mellitus also significantly increases the risk. Sustained high blood sugar levels damage the walls of small blood vessels and increase blood viscosity, contributing to thrombosis.
Other risk factors involve issues with blood flow or composition. Glaucoma, characterized by elevated pressure inside the eye, can compress the central retinal vein at the optic nerve head, contributing to CRVO. Blood clotting disorders (hypercoagulable states) can predispose an individual to clot formation, including in the retinal veins. High cholesterol (hyperlipidemia) and certain autoimmune diseases also increase the likelihood of RVO.
Diagnosing RVO and Potential Complications
Diagnosing RVO and assessing retinal damage requires specialized imaging by an ophthalmologist. Optical Coherence Tomography (OCT) is a non-invasive scan that provides cross-sectional images of the retina. OCT is used to measure the thickness and degree of fluid accumulation. Fluorescein Angiography involves injecting a fluorescent dye and taking rapid photographs of the retina to map blood flow. This test helps determine which areas of the retina are deprived of blood supply.
The most common threat to vision following RVO is Macular Edema, the swelling of the macula responsible for sharp, detailed vision. Leakage from the blocked vein causes this fluid accumulation, blurring central vision. Another serious complication is Neovascularization, the growth of fragile, abnormal new blood vessels in the retina or on the iris. This occurs because the oxygen-starved retina releases chemical signals that promote new vessel growth.
These new vessels are prone to leaking and bleeding into the vitreous gel, causing a vitreous hemorrhage and sudden, severe vision loss. If these vessels grow on the iris, they can block the eye’s natural drainage system. This leads to a dangerous spike in intraocular pressure called neovascular glaucoma. Early recognition of these complications is important because they dictate the necessary treatment to preserve sight.
Current Approaches to RVO Treatment
Since it is not possible to directly dissolve the clot and unblock the retinal vein, modern medical treatments focus on managing the complications that cause vision loss. The primary goal is reducing Macular Edema. The most common first-line treatment involves intravitreal injections, which deliver medication directly into the eye.
These injections often contain anti-Vascular Endothelial Growth Factor (anti-VEGF) agents, such as ranibizumab or aflibercept. Anti-VEGF agents block the growth factor responsible for causing blood vessel leakage and fluid accumulation. These treatments are highly effective at drying up retinal swelling and improving visual acuity. Corticosteroid medications, delivered via injection or sustained-release implant, are also used to reduce inflammation and leakage if the response to anti-VEGF agents is inadequate.
Managing Neovascularization requires a different approach to prevent vitreous hemorrhage and neovascular glaucoma. Laser therapy, specifically Panretinal Photocoagulation (PRP), is used to destroy the peripheral retina that is starved of oxygen and producing harmful growth factors. This targeted destruction reduces the overall demand for oxygen, causing the abnormal new vessels to regress. The long-term prognosis requires close collaboration with a primary care physician to manage underlying systemic conditions, such as optimizing blood pressure and blood sugar levels, to prevent future vascular events.