What is BRVO?
Branch retinal vein occlusion (BRVO) is when one of the smaller veins in the retina becomes blocked. This can occur from the formation of a blood clot, usually located at the spot where a small artery, hardened by age and/or high blood pressure compresses a retinal vein where they cross over. It usually affects one eye only. Vision may be blurred, distorted or obscured by intraocular bleeding.
The retina is an extension of the brain and forms a thin nerve tissue lining within the eye. It converts the light that is passed through the eye into electrical signals that travel along the optic nerve to your brain. The retina, like all other parts of the body needs a blood supply to keep it functioning.
The retinal veins drain the ‘used’ blood from the retina and take it back to the heart, while the arteries deliver nutrient and oxygen rich blood supply into and around the retina.
The blocking of a retinal vein, medically called an occlusion, occurs when a retinal artery compresses a vein as they cross, slowing the blood flow.
When blood flow through the vein is restricted, the pressure within the vein increases and forces fluid to leak out into the retina, causing blurred vision. The swelling in central vision is medically called ‘oedema’. The site of the blockage determines the degree of vision affected.
In more severe or untreated cases, the circulation is static such that retinal tissue starts to die off. When there are large areas of retina without sufficient nutrient and oxygen supply, the retina responds with the formation of a natural compound called vascular endothelial growth factor (VEGF). This process triggers abnormal new blood vessels to grow which can fill the eye cavity with blood causing complete vision loss or severe pain due to very high pressure (known as Rubeotic Glaucoma).
The eye is unusual in that the arteries and veins travel alongside each other in the retina as it is a thin film-like structure. At irregular intervals an artery can cross over an adjacent vein and thus predisposing the occlusion to happen.
The artery is most likely to do this if:
- Hypertension (high blood pressure)
- Diabetes
- Cholesterol
- Cardiovascular disease
- Smoking & obesity
It is essential to optimise the cardiovascular risk factors by insuring that the blood pressure, cholesterol and diabetes are optimally control.
Diagnoses and management involves a thorough eye assessment including checking the pupils’ response to bright light, measurement of intraocular pressure and examination of the retina after drops dilate the pupil. These drops will blur your vision and increase glare for a few hours. You are strongly discouraged from driving home after the assessment.
Ocular Coherence Tomography (OCT) ) is performed determine the degree of retinal swelling. It does not take long to acquire the OCT images, and it is non-invasive.
A Fluorescein Angiogram may be indicated in some patients. Fluorescein angiography has been performed for over 30 years and has been proven to be safe and well tolerated. The procedure involves injecting fluorescein dye into a vein in the back of the hand or in the bend of the elbow joint. Once the dye is injected, you will have a series of photos to document the dye circulating inside the eye, for a period of 5-10 minutes.
General Health: It is always essential for the blood pressure to be monitored and diabetes to be excluded so you will be encouraged to check with your local GP regarding your general health. Further blood tests may be necessary depending on each individual circumstance.
The eye is unusual in that the arteries and veins travel alongside each other in the retina. At irregular intervals an artery can cross over an adjacent vein, causing the occlusion to happen. There are a number of common risk factors that contribute to both the arteries and veins becoming damaged. These include:
- Hypertension (high blood pressure)
- Diabetes
- Cholesterol
- Cardiovascular disease
- Smoking & obesity
Less commonly the blood can become thick and sticky from a variety of causes including:
- Too much protein in the blood which causes circulation to slow down
- Hormone supplements or the contraceptive pill
It is important that these risk factors are controlled – regular visits to the GP to help regulate circulation problems, maintain good diabetic control and promote a healthy diet and lifestyle.
Treatment options vary depending on the severity of the occlusion. The choice of what treatment is best is made on an individual basis, where the clinical pattern and duration of the problem is assessed and taken into consideration.
Management can range between periods of observation through to injection and laser treatments.
Observation: In cases of BRVO, observation is the best approach for a couple of months to determine whether the occlusion will begin to resolve itself by creating ‘bypass channels’ so the blood can flow out of the eye again. Sometimes the blockage can be reduced if high blood pressure is controlled.
Anti-VEGF Drugs (Avastin/Eylea/Lucentis): Intravitreal Anti-VEGF drugs are very effective in reducing the retinal swelling (macular oedema) and have been routinely used worldwide for more than 10 years. The injections are performed in the clinic with antiseptic and local anaesthetic drops. The injections are safe and virtually pain-free. The risk of an infection is 1 in 20,000 (based on recent review of results at Bascom Palmer Eye Centre) and the injections rarely cause cataract formation.
Laser: In some cases of BRVO, laser treatment can be an effective management option. Laser treatment involves a procedure where a bright flashing light is used to cauterise leaking blood vessels and to facilitate drying of the leaking fluid by making little outflow channels. However, in some instances laser treatment needs to be deferred to a later stage, particularly if there are haemorrhages present within the retina.
It is crucial that the eye is checked at regular intervals, as directed by ophthalmologist, to detect and control any further deterioration. These visits are critically important to prevent any further vision loss and to preserve as much sight as possible.
What is CRVO?
Similar to BRVO, central retinal vein occlusion (CRVO) is a blockage to the central or ‘main’ retinal vein, located at the optic nerve. Haemorrhages can be scattered throughout the retina, and often the central portion of the retina, the macula, can become swollen.
The retina is an extension of the brain and forms a thin nerve tissue lining within the eye. It converts the light that is passed through the eye into electrical signals that travel along the optic nerve to your brain. The retina, like all other parts of the body needs a blood supply to keep it functioning.
The retina has the highest oxygen demands in the body and has 2 circulation systems: the retinal blood vessels within the inner layers of the retina and the choroid (vessels to nourish the deeper layers). The retinal veins drain the ‘used’ blood from the retina and take it back to the heart, while the arteries deliver nutrient and oxygen rich blood supply into and around the retina through the Central Retinal Vein within the Optic Nerve.
If the central retinal vein is kinked or blocked by a hardened artery, the blocked venous drainage causes the circulation to stagnate and the internal pressure elevates.
Unfortunately, with a CRVO sight is generally affected. This may range from mild to severe blurred and dim vision.
When blood flow through the vein is restricted, the pressure within the vein increases and forces fluid to leak out into the retina, causing blurred vision. The swelling in central vision is medically called ‘oedema’. The site of the blockage determines the degree of vision affected.
Typically, multiple small haemorrhages also occur because blood cells themselves also leak out into the retina due to the high venous pressure.
In more severe or untreated cases, the circulation is static such that retinal tissue starts to die off. When there are large areas of retina without sufficient nutrient and oxygen supply, the retina responds with the formation of a natural compound called vascular endothelial growth factor (VEGF). This process triggers abnormal new blood vessels to grow which can fill the eye cavity with blood causing complete vision loss or severe pain due to very high pressure (known as Rubeotic Glaucoma).
The risk factors that make people susceptible to CRVO are:
- Increasing age
- High blood pressure
- Cholesterol or triglyceride problems
- Glaucoma
- Diabetes
Less commonly the blood can become thick and sticky from a variety of causes including:
- Too much protein in the blood which causes circulation to slow down
- Hormone supplements or the contraceptive pill
Diagnosis and management of central retinal vein occlusion involves a thorough eye assessment including checking the pupils’ response to bright light, measurement of intraocular pressure and examination of the retina after drops dilate the pupil.
A Fluorescein Angiogram may be indicated in some patients. Fluorescein angiography has been performed for over 30 years and has been proven to be safe and well tolerated. The procedure involves injecting fluorescein dye into a vein in the back of the hand or in the bend of the elbow joint. Once the dye is injected, you will have a series of photos to document the dye circulating inside the eye and asses the degree of blockage, for a period of 5-10 minutes.
An OCT (Ocular Coherence Tomography) determines the degree of retinal swelling by scanning the eye like an ultrasound. This takes a very short time and is non-invasive.
General Health: It is always essential for the blood pressure to be monitored and diabetes to be excluded so you will be encouraged to check with your local GP regarding your general health. Further blood tests may be necessary depending on each individual circumstance.
Treatment options vary depending on the severity of the CRVO. The benefits and potential complications of the different treatment options need detailed discussion after a thorough initial assessment of the eye. In most cases some benefit can be achieved with treatment options.
Anti-VEGF Drugs (Avastin/Eylea/Lucentis): Intravitreal Anti-VEGF drugs are very effective in reducing the retinal swelling (macular oedema) and have been routinely used worldwide for more than 10 years. The injections are performed in the clinic with antiseptic and local anaesthetic drops. The injections are safe and virtually pain-free. The risk of an infection is 1 in 20,000 (based on recent review of results at Bascom Palmer Eye Centre) and the injections rarely cause cataract formation.
Choroidal Anastomosis Bypass: A special high powered laser creates a connection between the retina and a deeper (choroidal) circulation layer within the eye. This procedure can re-establish retinal circulation but takes several months to achieve adequate flow and often requires anti-VEGF therapy for up to 12 months.
Follow up
It is crucial with CRVO that the eye is checked at regular intervals to detect and control any further deterioration. These visits are critically important to prevent the eye becoming totally blind and painful and to preserve as much sight as possible.