Vein & Artery Occlusions

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Retinal Artery Occlusions and Retinal Vein Occlusions

Within the eye, the retina plays a vital role. This photosensitive (sensitive to light forms) layer of tissue, located in the back of the eye, converts light and images that enter through the lens into nerve signals. These signals then travel along the optic nerve, which transforms them into images, enabling you to see.

For the retina to do this, a constant supply of blood and oxygen is needed. But should retinal artery occlusions (RAO) or retinal vein occlusions (RVO) develop, this precious
oxygenated blood is prevented from reaching the retina. This may result in eye inflammation and swelling, and eventually, unhealthy new blood vessel growth or permanent vision loss.

How Do Artery and Vein Occlusions Form?

Arteries transport blood from the heart throughout the body, while veins return all of the tissues’ blood to the heart. Oxygenated blood is delivered by the retinal vascular system; its main components are the central retinal artery (extending from the neck’s internal carotid artery) and the central retinal vein.

Branching off from the optic nerve, the arteries and veins (which have thin walls) travel together within the retina, becoming smaller, and eventually binding to each other. But for people with high blood pressure (hypertension), arterial walls can thicken and harden over time (atherosclerosis). This can compress the adjacent veins, slowing and stopping blood flow, and causing ruptures in the capillaries, the smallest and most numerous blood vessels. Pressure may build, leading to retinal bleeding and inflammation.

Significant retinal leakage can cause swelling in the macula (macular edema). This can be serious, as the macula controls sharp, straight-ahead vision. As the retinal blood loss worsens, this may lead to unhealthy new blood vessel growth or permanent vision loss.

• How Occlusions Affect Retinal Arteries

  While retinal and vein occlusions have some similarities, depending on the specific area affected, there are different types.

  A branch retinal artery occlusion (BRAO) develops when a blood clot forms in a branch that stems from the central retinal artery. If oxygenated blood doesn’t reach the macula, you may lose central vision. With the more serious central retinal artery occlusion (CRAO, or eye stroke), you may have blind spots, distorted vision, and peripheral vision loss. CRAOs’ main symptom is sudden, painless vision loss. They may prevent retinal blood flow and cause severe vision loss.

  Both BRAOs and CRAOs should be treated as medical emergencies, as they may indicate an increased risk of a cerebral stroke. Furthermore, CRAO can lead to irreversible vision loss if not treated within 24 hours. The sooner you treat it, the better your chances of preserving some vision.

• How Occlusions Affect Retinal Veins

  A blockage in the main retinal vein is a central retinal vein occlusion (CRVO). A blockage in a smaller vein is a branch retinal vein occlusion (BRVO). If BRVOs occur outside of the eye's center, you may have no symptoms. Typically, they cause a painless, sudden loss of vision, but they can cause blood and other fluids to leak into the retina. BRVO symptoms may include floaters, loss of peripheral vision, and distorted or blurry central vision. There may also be bleeding in the vitreous, the clear, jelly-like substance filling the eye’s center.

  With CRVOs, blockages can cause structural damage to the veins, leading to retinal bleeding and fluid leakage. This vein damage results in new, fragile veins forming. These veins are prone to bleeding and leaking and can cause floaters to appear. CRVOs are generally associated with such underlying conditions as high blood pressure, diabetes, glaucoma, and blood disorders.

• What Are Typical Risk Factors?

  Research suggests that retinal artery occlusion patients are usually in their 60s, with men developing it more than women. Occlusions generally last for only a few seconds or minutes if the blood flow is restored. They usually target a single eye; only 1-2% of cases involve both eyes. Among their common risk factors are:

  • Smoking
  • Being overweight or obese (having an increased body mass index)
  • Cardiovascular disease
  • Diabetes
  • High blood pressure, especially among senior patients
  • High cholesterol
  • Narrowing of the carotid artery
  • Glaucoma (for BRVOs)
  • For younger BRVO patients, there may be an abnormal blood clotting tendency

Occlusion Diagnosis and Treatment

If you suspect a vascular event, your retina specialist should perform a thorough eye exam. For a mild occlusion, they’ll typically just monitor your eyes. This exam allows doctors to assess your eye’s health and function by checking your vision, measuring your eye pressure, and taking your blood pressure.

Retinal specialists will dilate your eyes, by applying special eye drops that keep the pupil open, providing a closer look at your retina. Other diagnostic tests may include:

• Ophthalmoscopy – An instrument called an ophthalmoscope enables doctors to observe and assess any retinal damage. For patients with diabetes, this should be performed at least once every year.
• Fluorescein angiography – This test highlights the eye’s blood vessels, with a colored dye injected into the bloodstream. Your doctor uses it to take pictures and analyze the images for signs of closed, broken, or leaking blood vessels.
• Optical coherence tomography (OCT) – Infrared light captures cross-sectional retinal images to check if fluid leaks into the retinal tissue.
• Indocyanine green angiography – A dye that lights up when exposed to infrared light is used to examine the retina’s deeper blood vessels.

Currently, there are no cures for retinal artery or vein occlusions. You may be advised to properly manage any underlying conditions and risk factors, like high blood pressure or cardiovascular disease. For occlusions requiring treatment, the primary goal is to seal leaking blood vessels. Should you develop macular edema or bleeding, you may be treated with injectable medications called anti-vascular endothelial growth factor (anti-VEGF) medications.

Anti-VEGFs help stop the growth of abnormal blood vessels by inhibiting the responsible protein. They’re injected directly into the eye’s vitreous, using a very thin needle. Anti-VEGFs are effective in managing retinal vascular diseases and may help you maintain your vision. Focal laser therapy or surgery (photocoagulation) may also be necessary. With this procedure, a high-energy laser beam breaks down blood vessel damage or seals leaking blood vessels.

In most cases, retinal occlusion patients do well. If you have only macular edema, injections are effective, although they’ll need to be continued for several years until the blood vessels repair themselves. However, if you experience macular blood vessel loss, you may have permanent vision loss.