What Causes Retinal Vein Occlusion? Risk Factors Explained

Retinal vein occlusion is one of the more common causes of sudden vision loss in one eye, affecting an estimated one to two per cent of people over 40. It happens when a vein carrying blood away from the retina becomes blocked.

What makes the condition worth understanding is that it rarely happens in isolation. In most cases, it reflects the state of your blood vessels more broadly, which means the causes are often manageable. This page explains why occlusions develop, which risk factors carry the most weight, and what can be done to reduce your risk.

If you have already been diagnosed and want to know about symptoms, treatment and recovery, see our guide to living with retinal vein occlusion.

What causes retinal vein occlusion?

A retinal vein occlusion occurs when blood flow through a retinal vein is obstructed. Two mechanisms are usually involved, and they often work together.

The first is compression. Retinal arteries and veins run alongside each other and share a common outer sheath where they cross. When the artery wall thickens and stiffens, which happens with age, high blood pressure and atherosclerosis, it presses on the vein at the crossing point. The vein narrows, flow slows, and a clot can form.

The second is clot formation itself. Slower or more turbulent blood flow, along with conditions that make blood more likely to clot, allows a thrombus to develop and block the vein.

Once the vein is blocked, blood cannot drain properly. Pressure rises in the vessel, and blood and fluid leak into the retina. The resulting swelling, particularly at the macula, is what causes vision to blur.

Where the blockage sits determines the type. An occlusion in the main retinal vein is a central retinal vein occlusion (CRVO); one in a smaller branch vein, usually at an artery crossing point, is a branch retinal vein occlusion (BRVO). Occlusions are also described as ischaemic or non-ischaemic depending on how much circulation is lost, which affects both the outlook and the risk of further complications.

High blood pressure: the leading cause

Of all the contributing factors, high blood pressure is the most significant. It drives the arterial changes that compress retinal veins at crossing points, and it is present in a large proportion of people who develop an occlusion.

Blood pressure is also the risk factor most within reach. Uncontrolled hypertension is often only discovered after an eye event, which is why an occlusion is frequently the trigger for a broader health review. If you have been diagnosed with high blood pressure, keeping it within your target range is the single most effective step you can take to protect your remaining vision and your other eye.

Other medical conditions that raise your risk

Several other conditions are consistently associated with retinal vein occlusion:

• Diabetes. Raised blood glucose damages small blood vessels throughout the body, including those in the retina. People with diabetes are also at risk of diabetic retinopathy, a separate retinal vascular condition.
• High cholesterol. Elevated levels contribute to the arterial thickening that compresses retinal veins.
• Glaucoma and raised eye pressure. Increased pressure inside the eye is an established risk factor, particularly for central occlusions.
• Cardiovascular disease. Existing vascular disease reflects the same underlying processes that lead to retinal occlusions.
• Blood clotting disorders. These are an uncommon cause overall but are considered more seriously in younger patients, where the usual vascular risk factors are often absent.

Age and lifestyle risk factors

Age is the strongest non-modifiable factor. Most occlusions occur after 50, and risk climbs steadily from there as blood vessels stiffen with age.

Smoking raises risk through its effect on blood vessel walls and on clotting. Physical inactivity, excess weight and a diet that contributes to raised blood pressure and cholesterol all play a part, largely through their influence on the conditions above rather than as independent causes.

The practical implication is that a substantial share of overall risk sits in factors that respond to treatment or to changes in daily habits.

Why retinal vein occlusion can signal a wider health problem

Because retinal vein occlusion shares its risk factors with cardiovascular disease, people who experience one have a higher likelihood of other vascular events, including stroke. The retina offers a rare direct view of small blood vessels, so an occlusion can be the first visible evidence of a vascular problem elsewhere.

This is why assessment usually extends beyond the eye. A diagnosis is worth treating as a prompt for a full cardiovascular review with your GP, even where you have felt entirely well.

Protecting your other eye

One of the most common questions after a diagnosis is whether the same thing will happen in the other eye. It can. Reported figures suggest somewhere between 6 and 17 per cent of patients go on to develop an occlusion in the fellow eye, because the underlying risk factors affect both.

That risk is not fixed. Controlling blood pressure, cholesterol and blood glucose reduces it meaningfully. In some cases, particularly where clotting risk is a factor, your doctor may consider aspirin or other medication, though this is an individual decision that depends on your overall health and any bleeding risk. Regular eye examinations allow changes in the unaffected eye to be identified early.

How your risk is assessed

Assessment after a retinal vein occlusion looks at both the eye and your general vascular health. Alongside a dilated eye examination and retinal imaging, you can expect:

•   Blood pressure measurement, often repeated rather than taken once
•   Blood tests for cholesterol and blood glucose or HbA1c
•   Measurement of eye pressure to check for glaucoma
•   In younger patients, or where no usual risk factors are present, additional tests for clotting disorders

Your ophthalmologist and GP will usually share these results so that eye care and vascular management run together. If you notice any sudden change in your vision, seek assessment promptly. Our guide to living with retinal vein occlusion covers symptoms, diagnosis and treatment in detail.

Reducing your risk

Prevention centres on the same measures that protect your heart and blood vessels generally:

•   Keep blood pressure within the range your doctor has set, and take prescribed medication consistently
•   Manage cholesterol and blood glucose through diet, activity and medication where needed
•   Stop smoking. This is among the highest impact changes for vascular health
•   Stay physically active and maintain a healthy weight
•   Have regular eye examinations, particularly if you are over 50 or have diabetes, high blood pressure or glaucoma

None of these guarantee that an occlusion will not occur, but together they reduce the likelihood and improve outcomes if one does.

Frequently asked questions

What is the most common cause of central retinal vein occlusion?

High blood pressure is the most common underlying contributor. It drives the arterial changes that compress retinal veins and is present in a large proportion of cases, particularly in patients over 50. Diabetes, high cholesterol and glaucoma are also frequently involved

What is the main risk factor for retinal vein occlusion?

Advancing age combined with high blood pressure. Other significant factors include diabetes, atherosclerosis, glaucoma, high cholesterol and smoking.

Can retinal vein occlusion be prevented?

Not entirely, since age and some medical conditions cannot be removed as factors. But because most cases are driven by manageable vascular risk, controlling blood pressure, cholesterol and blood glucose, along with not smoking and having regular eye checks, meaningfully reduces the risk.

Speak with our retinal team

If you have risk factors for retinal vein occlusion, or you have noticed a change in your vision, an assessment is worthwhile. Mornington Peninsula Eye Clinic provides specialist retinal care including diagnosis, treatment and ongoing monitoring. Contact us on (03) 9070 3580 to arrange an appointment.

Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.

References:

Retinal Vein Occlusion (RVO)

https://my.clevelandclinic.org/health/diseases/14206-retinal-vein-occlusion-rvo#:~:text=Many%20people%20with%20retinal%20vein,tailor%20treatment%20to%20your%20needs.

Central Retinal Vein Occlusion

https://www.ncbi.nlm.nih.gov/books/NBK525985/

What Is Retinal Vein Occlusion?

https://www.webmd.com/eye-health/retinal-vein-occlusion

Retinal vein occlusion

https://medlineplus.gov/ency/article/007330.htm