Retinal Vein Occlusion
What is a retinal vein occlusion?
Retinal vein occlusion is a common cause of sudden painless reduction in vision. It occurs when a blood clot forms in a retinal vein. The retina is the thin membrane that lines the inner surface of the back of the eye. It is similar to the film of a camera. Blockage of one of the veins draining blood out of the eye causes blood and other fluids to leak into the retina causing swelling as well as lack of oxygen. This interferes with the light receptor cells and reduces vision.
The condition is uncommon under the age of 60 but becomes more frequent in later life. There are two types of retinal vein occlusion, Central Retinal and Branch Retinal Occlusion.
• Central Retinal Vein Occlusion is due to obstruction of the main vein formed from the four branches.
• Branch Retinal Vein occlusions are due to obstruction in any of the retinal veins.
What causes a retinal vein occlusion?
A clot forming in the retinal vein results in complete or near-complete obstruction of blood flow. The exact cause of this event is generally unknown but a number of common conditions increase the risk of retinal vein occlusion occurring.
• High blood pressure
• High cholesterol
• A number of rare blood disorders
Prevention and systemic treatment
It is essential to identify and treat any risk factors in order to minimize the risk to the other eye and prevent a further vein occlusion in the affected eye. Treatment of the following risk factors reduces the risk of a further vein occlusion in both eyes. Without treatment there is a high risk of recurrence causing further damage to the sight of the affected eye and also damaging the sight of the other eye:
• High blood pressure: If your blood pressure is higher than 140/80 on several occasions, treatment is normally advisable.
• Raised blood cholesterol: Discuss diet modification with your general practitioner or dietician. Treatment with tablets is normally highly effective.
• Glaucoma: In this common eye condition, the pressure in the eye is raised and can cause gradual loss of peripheral vision. It can also increase the risk of another retinal vein occlusion. Treatment with drops to reduce the pressure is normally highly effective at preserving sight and presenting further retinal vein occlusions.
• Diabetes: Retinal vein occlusions are more common amongst people with diabetes. Detection of diabetes and good control is essential in order to preserve vision
• Smoking: The more you smoke, the greater the risk of another vein occlusion. Ask you general practitioner if you need help to stop smoking
• Rare blood disorders: these are normally identified by simple blood tests. In the unlikely event that this is the case, treatment is supervised by a specialist in blood disorders
Treatment of the eye
Persistent swelling (edema) at the centre of the retina (the macula) is the main cause of permanent loss of central vision. Several treatment options exist, depending on the severity and amount of retinal ischemia caused by the vein occlusion.
• Intravitreal injections: these are usually the mainstay of treatment, and help to alleviate the macular edema as well as decrease the ‘drive’ in the eye for new vessel formation.
• Laser: This may assist at a later stage. Not everyone requires laser.
Are there any later complications?
In certain cases, the retina does not get enough oxygen and produces a chemical factor which causes new blood vessels to grow on the retina and iris. This can cause high pressure in the eye which is painful and can lead to blindness. Timeous follow-up and treatment may help to prevent these new blood vessels from growing.
Will the other eye become affected?
The second eye may become affected in approximately 10% of people, but only 25% of these occur within 5 years. Thus is there is an increased risk, but with adequate risk factor modification, most people will not have a second eye involved.
Will glasses help?
Not specifically. The reason for poor vision is macular edema, which is treated as discussed above.
Patients with a central retinal vein occlusion are reviewed every four to eight weeks for approximately 6 months. Thereafter, follow-up intervals are usually spaced out on an individual basis, depending on the response to treatment.
Patients with a branch retinal vein occlusion may be followed up less frequently. The follow-up intervals and treatment are individualized on a patient-by-patient basis, depending on retinal perfusion and macular edema.