Branch retinal vein occlusion occurs when a small artery, hardened by age and/or high blood pressure compresses or squashes a retinal vein where they cross over. It usually affects only one eye. Vision may be blurred, distorted or obscured by intraocular bleeding.
How does BRVO occur?
The retina is part of the brain and forms a thin nerve tissue lining within the eye. The retina functions like the film in a camera. 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 to take it back to the heart, while the arteries take the blood supply into and around the retina at high pressure.
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 so much that the blood stagnates. This can be imagined as the effect on watering the garden if you step down on the hose thereby blocking off or occluding the flow of water.
What does the blockage cause?
When blood flow through the vein is restricted, the pressure within the vein increases and forces fluid to leak out into the retina which causes blurred vision because the retina cannot function properly. The swelling in central vision is medically called ‘oedema’. The site of the blockage determines the degree or extent of the vision affected.
What are the risk factors?
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)
- 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.
How is BRVO diagnosed?
Diagnoses and then management of BRVO involves a thorough eye assessment including checking the pupil’s response to light, measurement of intraocular pressure and examination of the retina.
An OCT (Ocular Coherence Tomography) determines the degree of retinal swelling by scanning the eye with an ultrasound. This takes a very short time and is uninvasive.
A Fluorescein Angiogram is performed to assess the circulation and the degree of the blockage. This procedure is where a dye is injected into the hand and then the eye is photographed over a period of five minutes as the dye flows through.
What are the treatment options?
BRVO is a condition that can be significantly helped with modern treatment. The choice of what treatment is best can only be made on an individual basis where the clinical pattern and duration of the problem are assessed and then the options discussed in light of all the findings.
Management can range between periods of observation through to laser surgery.
Types of Treatment
Observation: In many patients, 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 kinking/blockage can be reduced if high blood pressure is controlled.
Avastin: This drug is very effective in reducing the retinal swelling (macular oedema). It is part of a class of drugs called anti-VEGF agents (the others are Lucentis and Eylea). Sluggish retinal circulation results in low oxygen levels which triggers production of “Vascular Endothelial Growth Factor” which makes retinal blood vessels leaky and occasionally grows in abnormal areas. Avastin has been routinely used by A/Prof Heriot and others worldwide for almost 10 years. The drug is injected painlessly into the eye in our consulting rooms.
Laser: Is the traditional treatment option which “prunes” areas of poor circulation just like one would trim a plant that is not doing well. This ensures that the nourishment goes to the key parts of the plant rather than trying to supply everything – with the consequence that nothing is well supplied. 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. Laser treatment can be very effective in simple branch vein occlusion particularly if there is not too much retinal bruising. Retinal bruising or haemorrhages prevents the laser working. As such, sometimes it is necessary to defer laser treatment until the haemorrhages diminish. This, unfortunately, leaves poor vision for a longer time and also increases the prospect of permanent visual reduction. The good thing about laser treatment is that it can be delivered in my consulting room and has virtually no direct side-effects. It is, however, effective in only a small group of patients with a branch vein occlusion.