The retina is a complex piece of tissue. It’s responsible for receiving light coming into the eye, converting it into a neural signal, and sending it through a series of cells, down the optic nerve, where it eventually reaches the visual parts of the brain. After the cells of the retina have sent on their signals, they need to reset to do it all over again. The retina is supported by various other tissues in order to achieve this, all of which need oxygen and nutrients to perform properly.
Blood Vessels of the Retina
Due to its constant activity, the retina needs a constant supply of oxygen and blood flow through its blood circulation system. The main retinal blood vessels include the central retinal artery and the central retinal vein. The central retinal artery carries high-oxygen and nutrient-rich blood flow into the retina while the central retinal vein takes deoxygenated blood out of the retina to be replenished back at the heart and lungs.
Similar to other blood vessels of the body, it is possible to develop a blockage in a retinal blood vessel, whether an artery or a vein. In medical terms, this is known as an artery or vein occlusion. The blood vessels of the eye can be subject to various different types of occlusions, including central retinal vein occlusion, branch retinal vein occlusion, central retinal artery occlusion, or branch retinal artery occlusion. Compared to blockages of the retinal arteries, retinal vein occlusions are more common.
What Causes a Retinal Vein Occlusion?
A retinal vein occlusion can occur in either the main retinal vein- the central retinal vein, which is then termed a central retinal vein occlusion (CRVO), or in a smaller blood vessel, called a branch retinal vein occlusion (BRVO).
The main cause of a retinal vein occlusion is the formation of a blood clot, which typically occurs at the point where a retinal artery crosses over a vein. The result of this is poor blood flow through that point of the retinal circulation. As the outflow of blood is slowed, it accumulates behind the point of blockage. This leads to swelling, including around the macula. This is known as macular edema, which can result in central vision loss.
Other effects of a retinal vein occlusion include haemorrhaging and fluid leakage into the retina (bleeding). This leakage of blood into the surrounding retinal tissues can cause further cellular damage and vision loss.
Symptoms of Retinal Vein Occlusion
The symptoms of retinal vein occlusions are non-specific. That means, there is not one single symptom that would make you realise you’re experiencing a retinal vein occlusion.
In most cases retinal vein occlusion occurs just in the one eye. If the retinal vessel occlusion results in swelling of the macula (macular edema), you will notice a gradual, painless loss of vision in your central sight. In some cases, the loss of vision can be quite sudden. However, if the blood clot occurs in a retinal vessel further away from the macula, you may actually not be aware of any changes to your vision. In situations that involve a large vitreous hemorrhage, where there is a significant bleed into the space of the eyeball containing the retina, you may experience sudden complete vision loss in that eye.
Some people also report seeing dark specks, lines, or squiggles in their vision. These are known as floaters. During a retinal vein occlusion, floaters are typically droplets of blood leaking into the vitreous.
Risk Factors for Retinal Vein Occlusion
Risk factors are characteristics of a person that make them more likely to experience a disease or condition. For any condition, including central or branch retinal vein occlusions, having a risk factor does not guarantee you will develop the condition. Conversely, not having any of the risk factors does not rule you out from ever experiencing the disease.
The risk factors relevant to retinal vein occlusions are similar to those for strokes and heart attacks. They include:
- Older age (particularly being over the age of 60)
- Hypertension (high blood pressure)
- Hypercholesterolaemia (high blood cholesterol levels)
- Diabetes (a systemic disease involving elevated blood sugar levels)
- Being overweight or obese
It is possible to reduce your risk of retinal vein occlusion by managing these modifiable risk factors. Apart from getting older, all other factors can be controlled.
Diagnosis and Treatment
Either an optometrist or ophthalmologist will be able to diagnose a retinal vein occlusion. They achieve this by viewing the whole retina and the retinal blood vessels, assessing for any haemorrhaging or retinal swelling that may be due to a blocked vein.
If you’ve attended to an optometrist who diagnoses a retinal vein occlusion, you’ll be then referred to an ophthalmologist for treatment.
For a better view of the whole retina, you will most likely have dilating eyedrops instilled, which widen the pupil and temporarily stop it from constricting, which its natural response to light.
Macular edema is most easily visualised using a test called optical coherence tomography. Optical coherence tomography will also be used to continue monitoring the improvement of the macular edema over time. Another test called fluorescein angiography involves the injection of a dye through you veins, which helps to highlight the location of blood clots, any abnormal blood vessels, and the overall state of your retinal veins and arteries.
Treatment options will depend on the specifics of your condition. If macular edema is present, you may be recommended an eye injection of a drug called anti vascular endothelial growth factor. These injections are typically repeated until the swelling has resolved. Anti vascular endothelial growth factor injections can also be used if the retina begins to develop abnormal new blood vessels. These new blood vessels are a risk for a secondary disease called neovascular glaucoma.
Laser treatment is also an option, both for managing any retinal swelling as well as the growth of new blood vessels. Any unusual changes to your vision should never be ignored, particularly areas of vision loss.
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Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.
Retinal vein occlusion.
What is Branch Retinal Vein occlusion (BRVo)?