Central retinal vein occlusion (CRVO) causes very poor vision because the circulation within the eye slows down. The effects can range from slightly blurry vision through to a blind, painful eye.
How does CRVO occur?
The retina is an extension of the brain and forming a thin light sensitive lining inside the eye and functions like a camera film or digital chip. The retina has the highest oxygen demands in the body and has 2 circulation systems to cope: The retinal blood vessels within the inner layers of the retina itself and the choroidal; vessels to nourish the deeper layers. The arteries bring in fresh blood and the veins channel the ‘used’ blood out 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.
What does the blockage cause?
Unfortunately, with a CRVO sight is generally affected. This may range from mild to severe blurred and dim. This occurs due the same thigs that control the watering from a garden sprinkler system: fluid seeps out just like a “soaker hose” because the pipes develop “punctures” due to the low oxygen supply nourishing the blood vessels themselves and the higher the pressure the more fluid leaks out. This accumulation of fluid is medically called ‘oedema’ and diminishes sight. Usually multiple small haemorrhages occur because blood cells themselves get out not just the fluid due to the high venous pressure. In severe or untreated cases the circulation is so static that retinal tissue starts to die off. When there are large areas “screaming out for oxygen” the retina responds with the formation of a natural compound called Vascular Endothelial Growth Factor (VEGF) This triggers abnormal new blood vessels to grow which can fill the eye cavity with blood causing virtually complete vision loss or severe pain due to very high pressure (known as Rubeotic Glaucoma).
What are the risk factors?
The risk factors that make people susceptible to CRVO are:
- Incerasing age
- High blood pressure
- Cholesterol or triglyceride problems
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
How is CRVO diagnosed?
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 is performed to assess the circulation and the degree of blockage. During this procedure a dye is injected into a vein on the back of your hand and the eye photographed over a period of five minutes as the dye runs through the body. The dye is eliminated through the kidneys over the next 24 hours.
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.
What are the treatment options?
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.
Lucentis, Eylea or Avastin: These drugs are the usual treatment for macular oedema (retinal swelling) caused by the slowdown and high pressure within the retinal vessels. These are called anti-VEGF drugs because the sluggish retinal circulation results in low oxygen levels and this triggers production of “vascular endothelial growth factor” (VEGF) which makes retinal blood vessels leaky and occasionally grow in abnormal areas. Both of Eylea and Lucentis are covered under the pharmaceutical benefits scheme and are injected painlessly into the eye in the consulting rooms.
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.
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.