What is retinal vascular occlusion?

What is retinal vascular occlusion?

The retina is located at the back of the eye, and it is responsible for converting light into electrical impulses and transmitting it to the brain which turns it into images. There is a network of blood vessels supplying nutrients and oxygen called arteries, as well as a network of blood vessels removing the de-oxygenated blood called veins.

There is one main artery (central retinal artery) that enters the back of the eye through the optic nerve. The central retinal artery splits at the point of entry into two branches, one supplying the top part and the other supplying the bottom part of the retina. These two branches in turn split again in two, one to supply blood to the left, and the other to the right of the retina.

Like the arteries, there are four branch veins that join to form the central retinal vein that leaves the eye through the optic nerve at the back of your eye. The branch veins split into other much smaller veins which spread out all over the retina.

Retinal vascular occlusion is caused by a blockage (occlusion) in one of the blood vessels in the retina, obstructing or completely blocking the normal blood flow.

Types of RVO

There are two main types of retinal vascular occlusions:

1. Retinal artery occlusion (RAO) is commonly caused by atherosclerosis or an embolus. Atherosclerosis is the build-up and hardening of fat, cholesterol, calcium, and other blood substances called plaque. The plaque causes arteries to narrow over time, impeding or even completely cutting off blood flow.

In some instances, pieces of plaque formed in bigger arteries near the heart or in the neck, can break off creating a blood clot or an embolism which can potentially block other smaller arteries like those in the retina. In less common instances, retinal artery occlusion can be caused by the inflammation of an artery wall called vasculitis, trauma, or other systemic diseases such as sickle cell disease.

Central retinal artery ccclusion (CRAO) is caused if the central artery has a blockage before it enters the eye, therefore allowing little to no blood to enter the eye, leading to all of the vision being affected in that eye.

Branch retinal artery occlusion (BRAO) is caused if one of the branches has a blockage, only affecting a certain area of your vision.

When any of the retinal arteries become blocked, it prevents the inflow of blood to the retinal cells and tissue, depriving it from the oxygen and nutrients it needs to function and live, potentially causing damage to these cells and tissue and affecting your vision

2. Retinal vein occlusion (RVO) is commonly caused by blood clots forming in the vein called thrombosis. In some cases, it can be caused by atherosclerosis where the affected artery presses onto the vein causing it to narrow, impeding the blood flow which can a clot to form, blocking the vein.

Central Retinal Vein Occlusion (CRVO) is caused if the central vein leaving the retina has a blockage, therefore allowing little to no blood to exit the eye. This can lead to all of the vision being affected in that eye.

Branch Retinal Vein Occlusion (BRVO) is caused if one of the branches has a blockage, only affecting a certain area of your vision.

When any of the retinal veins become blocked, it prevents the outflow of blood which can cause swelling, pooling, and potentially the leaking of blood and fluid (haemorrhaging) into the retina which could cause damage to the retina and affect your vision.

How common is it?

RVO is the most common of the two occlusions, affecting about one to two percent of people over 40, with most cases occurring in people over 60. It usually only occurs in one eye. RVO is the second most common retinal vascular disease, or condition that affects the retinal blood vessels, following diabetic retinopathy. If you notice any symptoms, even if it disappears after seconds or minutes, see a practitioner immediately.

Symptoms

Symptoms may vary from person to person depending on the type of the blockage, the severity of the blockage, the location, and the retinal damage that occurred during the blockage. It is usually painless and only occurs in one eye.

In some cases, you can have no noticeable symptoms, particularly if it happens in a smaller branch vessel towards the side of your vision. In other cases, it may present as:

• Blurred vision or loss of vision in one eye (full or partial) which may be permanent or may gradually get better depending on the degree of damage to the retina. Generally, in the case of a RAO, the chance of restoring vision is very low, resulting in permanent vision loss.
• An increase in eye pressure (in more severe cases).
• Floaters or dark spots in your vision.
• Difficulty judging distances, feeling clumsy, or misjudging steps or the position of objects due to the impact on three-dimensional vision. After a few months, you might find this becomes less of a problem when your brain starts to adjust to the new visual input it receives from your eyes, making the eye with the better vision your dominant eye.

Causes and risk factors

There are risk factors that can increase your likelihood of having retinal vascular occlusion, including:

• Age.
• Diabetes.
• High blood pressure.
• Blood clotting disorders.
• Glaucoma.
• Smoking.
• High cholesterol.
• Being overweight.

Reducing the risk of RVO

You can lower your risk by making healthy changes such as:

• Eating healthy.
• Controlling your blood pressure and keeping it in the normal range.
• If you have heart disease, getting treatment.
• Not smoking.
• Staying a healthy weight.
• Staying active.
• Controlling your cholesterol and keeping it in the normal range.
• If you have diabetes, controlling your diabetes and keeping your blood sugar at a normal rate.
• Speaking to your general practitioner if you have a family history of heart disease, high blood pressure, cholesterol, or strokes.

Diagnosis

Your eye care professional will conduct an examination of your eyes which may include:

• Checking your visual acuity, which is your ability to see at different distances. This can include recognising letters at varying distances.
• Assessing your peripheral vision with a visual field test, which is your ability to see in your side vision.
• Checking the retina at the back of your eye with an ophthalmoscope by shining a light into your eye and looking through different lenses, or using an optical coherence tomography scan (OCT) which creates a 3D cross section image to see the layers in the retina or taking a digital colour photo of the retina.
• Checking the surface of your eye and other structures within the eye with a microscope called a slit lamp.
• Measuring the pressure in your eyes.

Treatment

Your treatment will depend on the cause, location, severity of the blockage, and the extent of retinal damage. The goal of treatment is to prevent further sight loss from occurring. This may include:

• Injections in your eye called Anti-VEGF injections which can reduce inflammation and reduce the formation of abnormal blood vessels. Read this article for more information on Anti-VEGF injections.
• Steroid injections to reduce swelling.
• Laser treatment or panretinal photocoagulation (PRP), which can lessen the growth of new abnormal blood vessels and reduce fluid from leaking under the retina.
• Further tests by your general practitioner to determine any underlying causes.

As retinal vascular occlusions can often have no symptoms, it is important to have regular eye tests which can detect any abnormalities and allow for timely treatment to prevent further damage.

For more information

• Visit the Macular Disease Foundation’s RVO webpage.
• Always speak to your GP and eye care professional about the best treatment options for you.