Understanding Retinal Vascular Occlusion
Understanding Retinal Vascular Occlusion

Understanding Retinal Vascular Occlusion

Retinal vascular occlusion, also called retinal vein occlusion, is when the flow of blood through the retinal vein is interrupted or stopped. In this article, we look at the two types of retinal vascular occlusion, what causes the eye conditiona nd the treatment options available.

Retinal vascular occlusion, also called retinal vein occlusion, is when the flow of blood through the retinal vein is interrupted or stopped. The retina is a layer of cells at the back of the eye that is light sensitive and converts information on light and colour into electrical signals that are sent to the brain. If the flow of blood from the retina is stopped it can lead to leakage or swelling that interrupts the work of the eye. It is uncommon in people under 60, but chances of it happening are greater in later life.

There are two types of retinal vascular occlusion – BRVO and CRVO. Branch Retinal Vein Occlusion is when one of the four veins (the branches) that drains blood from the retina is obstructed. Central Retinal Vein Occlusion is when the main vein (where the four branch veins connect) is obstructed.

Signs and symptoms of Retinal Vascular Occlusion

Vascular occlusion is usually painless and minor blockages may have no symptoms at all. Symptoms can include:

What causes Retinal Vascular Occlusion?

Retinal Vascular Occlusion is caused by a blood clot forming in a branch vein or the central vein of the retina. There are a variety of factors that can increase the chances of a blood clot forming, including:

  • Smoking, which can thicken the blood and increase the chances of a clot.
  • High blood pressure.
  • Cholesterol.
  • Diabetes.
  • Glaucoma, which raises the pressure in the eye.
  • Blood disorders, which are rare but can cause dysfunction.

Taking steps to rectify or treat these conditions will help reduce the risk of blood clots forming as well as other complications.

Complications of Retinal Vascular Occlusion

There can be serious complications with retinal vascular occlusion that lead to further deterioration of your eyesight.

  • Macular Oedema. The macula is a central part of the retina, oedema is when the macula swells as a result of fluid build-up, impeding your vision.
  • Neovascularisation. When new blood vessels form and fluid from them is unable to drain away properly, it will increase pressure in the eye, causing further problems.
  • Detached retina. The retina is pulled away from the blood vessels that supply it with blood because of a build of fluid or irregular blood vessels forming.

Complications will not happen in every case, but can seriously impact the quality of vision, so it is important to follow up any early symptoms or side-effects.

The anatomy of the eye

The eye is constructed of four important components that work together to function:

The Cornea and Lens – These are at the front of the eye; they focus light directly onto the retina in the same way a camera lens focuses light onto film.

The Retina – This is a thin layer of cells at the back of the eye, they work by interpreting light and colour that enters through the lens and converts it into electrical signals.

The Optic Nerve – The nerve that connects to the eye and sends electric impulses to the brain where they are interpreted. 

The Retina

The retina is a light-sensitive layer of tissue that lines the back wall of the eye. Blood is carried to the retina by the retinal artery and taken away by the retinal vein, both can suffer from occlusion in the case of a blood clot or hardening/thinning of the inner walls.

Once the information has entered the eye through the lens, it reaches the retina and stimulates chemical and electrical impulses that are transmitted to the brain via the optic nerve. The photoreceptor cells on the retina are responsible for differentiating between colours and shades of light and dark. 

In the middle of the retina is the Fovea Centralis which is a tiny depression that is tightly packed with cones (a type of photoreceptor cell), and is responsible for activities that involve highly detailed visual activity like reading and driving.

How is Retinal Vascular Occlusion diagnosed? 

Initial diagnosis of retinal vascular occlusion will involve fairly standard eye tests used to detect a variety of eye conditions.

  • Visual Acuity Test. You will be asked to read increasingly small lines of letters on a standardised chart to check the sharpness of your vision.
  • Slit Lamp Examination. A test where a thin beam of light is shone into your eye to illuminate the front of it and inspected with a microscope.
  • Refraction Test. An eye doctor will ask you to look at various eye charts through lenses of different strengths. More in-depth tests may also be conducted, these include:
  • Fluorescein angiography. This is a test where a yellow fluorescein dye is injected into your bloodstream. Photographs of your retina, illuminated by the dye, will then be taken and allowing your doctor to examine the condition.
  • Optical coherence tomography. OCT is a non-invasive test that uses light waves to take cross-section images of your retina. It is used to measure the amount of retinal swelling and to determine which treatment will be beneficial.
  • Tonometry. A test that determines the intraocular pressure inside the eye. Increased pressure can cause glaucoma to develop, this test will help diagnose it.

You may also be given blood tests to check for rare blood disorders, diabetes, high cholesterol, or problems with blood clotting or thickening.

If a blockage is diagnosed, it may be necessary to continue to monitor how it progresses over a period of months to see if any complications arise from the initial problem.

How do you treat Retinal Vascular Occlusion? 

The key aim in treating retinal vascular occlusion is to ensure everything possible is done to prevent damage to the other eye if it is not too late. Currently, there are no treatments that can reverse the blockage, so if it is too severe then it is unlikely vision will be restored.

Less serious cases may result in some vision loss or none at all, depending on the severity and location of the blockage. If the central retinal vein is blocked, this is more likely to cause permanent vision loss than a blockage in a branch vein.

Treatment of underlying risks for Retinal Vascular Occlusion

Treatment of risk factors is the best way of preventing further problems, many of these recommendations are applicable to a wide range of health concerns including the eyes.

  • Treatment for high blood pressure. Losing weight, improving your diet, restricting consumption of salt, alcohol, and caffeine will help. Medication to lower blood pressure may also be necessary.
  • Treatment for glaucoma. Including eye drops, laser treatment, or surgery.
  • Managing diabetes. Managing blood sugar levels through diet, medication, or both.
  • Giving up smoking. Get advice from your GP or pharmacist on methods or products to quit smoking.
  • Treatment of blood disorders.
  • Lowering cholesterol. Losing weight, physical activity, quitting smoking, and potentially the use of statins can help with high cholesterol.

Without treatment, there is a high chance of reoccurrence, by addressing the various risk factors you can drastically reduce the risk of occlusion in the other eye and further problems in the affected eye.

Treatment of complications

If complications arise from the occlusion they will also need treatment – the two most serious complications are Macular Oedema and Neovascularisation.

Macular Oedema is swelling at the centre of the retina; the swelling is caused by leaky blood vessels. It can either be treated with medication that is injected into the eye or with laser treatment, sometimes both may be used.

  • Anti-VEGF drugs. Also known as “anti-vascular endothelial growth factor” drugs, this helps to reduce swelling in the eye and needs to be injected regularly over 1 – 2 years. Typically, they will be given every two months or less frequently as treatment continues.
  • Steroids. These are usually injected in the form of an implant four or five times over the course of a two-year treatment process.
  • Laser treatment. Typically, Macular Grid laser treatment is used, the aim is to stem the leakage from damaged blood vessels. 

Anti-VEGF and steroids can improve vision significantly – up to 55% of patients treated experienced notable improvement. Around a quarter of patients fail to experience any improvement with the use of injections. 

Neovascularisation is when new, abnormal blood vessels develop on the surface of the retina or at the front of the eye. Between twenty and thirty percent of people who suffer from retinal vascular occlusion will also get neovascularisation. Laser treatment is usually successful in preventing new blood vessels from developing – using a process called Pan Retinal Photocoagulation. This does not improve vision that has already deteriorated but is effective if performed at an early stage. 

Patients with central retinal vein occlusions will be reviewed quite regularly – once a month, or every two months – to try and use preventative treatment to stop the complications above. Those with branch retinal vein occlusions will be seen less often as there is less chance of complications and loss of vision.