Central Retinal Vein Occlusion (CRVO) affects the primary blood drainage system of the eye. It occurs when a blockage forms in the central retinal vein, the main vessel responsible for carrying deoxygenated blood away from the retina. This condition is second only to diabetic retinopathy as the most common retinal disorder. The sudden obstruction disrupts the eye’s circulatory balance, leading to a backup of blood and fluid. Since the retina relies on continuous blood flow, a blockage can result in severe visual impairment.
The Mechanism of Central Retinal Vein Occlusion
CRVO typically begins with a thrombus, or blood clot, forming in the central retinal vein where it crosses the central retinal artery near the optic nerve. The rigid artery, due to atherosclerotic changes, compresses the softer vein, causing turbulent blood flow and clot formation. This blockage forces blood to back up into the retinal capillaries, increasing pressure. The pressure causes fluid to leak out of the vessels into the retinal tissue, resulting in hemorrhage and edema.
The leakage causes the retina to swell, especially in the macula, the central area for sharp vision. Macular edema is the primary cause of vision reduction because accumulated fluid distorts the light-sensing cells. Vascular congestion leads to inadequate oxygen supply (ischemia). Oxygen deprivation causes the retina to release high levels of a signaling protein called Vascular Endothelial Growth Factor (VEGF). This protein, intended to stimulate new blood vessel growth, causes further vascular leakage and swelling.
CRVO is categorized into two subtypes: non-ischemic (perfused) and ischemic (non-perfused). Non-ischemic CRVO is more common, accounting for about 70% of cases, and generally carries a better visual outlook because blood flow is only partially compromised. Ischemic CRVO involves a more complete blockage and extensive capillary non-perfusion, leading to severe complications. Progression from the non-ischemic to the ischemic type can occur over time.
Identifying Common Risk Factors
High blood pressure (hypertension) is a major contributor to CRVO. Chronic stress on blood vessel walls promotes rigid changes in the central retinal artery that can compress the vein. Diabetes mellitus also damages and weakens blood vessels, making them more susceptible to blockages and clots.
High cholesterol and arteriosclerosis (hardening of the arteries) contribute to the narrowing of blood vessels. The condition primarily affects individuals over the age of 50, with risk increasing after age 65. Open-angle glaucoma, characterized by elevated pressure within the eye, is a local ocular risk factor. A tendency toward abnormal blood clotting (hypercoagulable state) may also be a factor.
Recognizing the Symptoms and Diagnosis
CRVO’s primary symptom is sudden, painless blurring or loss of vision, usually in one eye. Patients may notice this upon waking, though the onset is not always immediate. The severity of vision loss varies widely, depending on the extent of the blockage and subsequent macular swelling.
An ophthalmologist confirms the diagnosis through a dilated fundus examination, which provides a direct view of the retina. The characteristic appearance involves widespread retinal hemorrhages, often described as having a “blood and thunder” appearance, along with dilated and twisted retinal veins. The presence of swelling in the optic nerve head and cotton-wool spots, which are areas of nerve fiber layer damage, also supports the diagnosis.
Physicians rely on specialized imaging techniques to assess the damage. Optical Coherence Tomography (OCT) is a non-invasive scan that provides cross-sectional, high-resolution images of the retina. OCT is used to measure the thickness of the macula, quantifying the degree of fluid accumulation and swelling, which is the main cause of vision loss.
Fluorescein Angiography (FA) involves injecting a fluorescent dye into an arm vein and photographing the retina as the dye travels through the vessels. This test evaluates overall blood flow and determines the subtype of CRVO. FA helps differentiate between non-ischemic and ischemic forms by identifying areas of capillary non-perfusion, where blood flow has stopped. Non-perfusion helps predict the risk of developing neovascularization.
Treatment Strategies and Long-Term Management
CRVO treatment aims to resolve macular edema and prevent vision-threatening complications. The standard of care involves anti-VEGF agents, which are medications injected directly into the vitreous gel of the eye. These agents block the VEGF protein, preventing blood vessels from leaking and swelling.
Injections reduce macular thickness and improve visual acuity in many patients. Treatment often begins with a series of monthly injections, followed by a regimen that extends the interval between treatments. A steroid implant may be used as an alternative treatment, as it helps reduce inflammation and fluid leakage within the retina.
A risk of ischemic CRVO is the development of neovascularization, where fragile, abnormal new blood vessels grow on the retina or iris due to oxygen deprivation. These new vessels can bleed easily or lead to a rise in eye pressure, known as neovascular glaucoma. If neovascularization is detected, Panretinal Photocoagulation (PRP) laser treatment destroys the oxygen-starved peripheral retinal tissue, reducing the stimulus for VEGF production.
Long-term management involves regular follow-up visits to monitor for recurrence of macular edema or neovascularization. Patients require ongoing surveillance using OCT to track retinal thickness and visual acuity. Managing the underlying systemic risk factors, such as blood pressure, diabetes, and cholesterol levels, is essential to reduce the risk of future vascular events.