Impact of Retinal Vein Occlusions on the Eye
There are two major types of Retinal Vein Occlusion (RVO) that can affect an eye. Each type of RVO can have a slightly different type of impact and prognosis on the eye. The two major types of RVO are : Central Retinal vein occlusion (CRVO) and Branch Retinal Vein Occlusion (BRVO).
Learn more about each type of RVO and the impact it can have on the eye.
- Central Retinal Vein Occlusion
This occurs when the major vein taking blood away from the retina back to the heart becomes blocked. The typical patient would be over 50 years but around 10% can be under this age. As the condition affects the whole of the retina this is usually a more serious problem than its sister condition the branch retinal vein occlusion.
The precise level of eyesight decline varies markedly – but around 20-25% of patients would have vision decline such that the top letter on a chart would be difficult to identify. The good news is that in many more patients vision reduction is less severe and in around 10% of cases vision is barely affected at all.
The reasons for this wide variation are complex but essentially come down to how much impairment is produced on the tiny blood vessels that feed into the veins – called capillaries. If there is extensive damage to retinal capillaries as a result of the CRVO then very often the vision is very poor and prognosis for recovery is poor. However in many cases capillary damage is not severe and in such cases the potential for a beneficial impact of treatment is much more reasonable.
The other major cause of poor eyesight in CRVO is the development of swelling of the very central part of the retina – called the macula. The macula is the most sensitive part of the retina and provides us with our detailed vision. Any damage in the macula can produce a significant decline of vision. CRVO is prone to causing swelling of the macula – called macula oedema. If this is there are a number of ways we can treat this and a careful evaluation to determine the eligibility of treatment for macular oedema is required.
The final major potential impact from CRVO can occur weeks or even month after the onset of this condition. The development of abnormal blood vessel growth either in the retina or more commonly in CRVO over the iris can lead to the development of a very high eye pressure – this is called rubeotic glaucoma. Rubeotic glaucoma is perhaps the most feared end result of CRVO. patients with CRVO will be examined on a fairly regular interval to detect the earliest signs of abnormal blood vessel growth and if identified a recommendation for Laser treatment of the retina is usually made.
- Branch Retinal Vein Occlusion
Its estimated that around 6 in 1000 people over the age 64 will develop a BRVO over a four year period. This makes BRVO significantly more common than CRVO. Here only a single one of the four major branches of the central retinal vein are blocked. The impact of the blockage will to some extent depend on the precise branch involved and one the severity of the blockage. As with CRVO the extent of capillary damage that arises as a result of the BRVO is a major factor in determining the visual impact of BRVO on the eye. It is somewhat less common to develop very poor eyesight in BRVO.
Aside from capillary damage the other two major reasons for developing sight decline in BRVO are physical haemorrhage on the surface of the retina – especially when it involves the central part of the retina – the macula. The other major cause of poor sight is macular swelling as in CRVO. Finally months or even years down there can be abnormal blood vessel growth taking place in the retina in BRVO cases. Its generally very uncommon for the more serious blood vessel growth developing over the iris as in CRVO though this can happen too. More commonly new blood vessels growing in the retina may cause some internal bleeding – called vitreous haemorrhage – which can also result in further eyesight decline. For these reasons patients who develop BRVO will remain under some form of surveillance for some time – often for up-to two or three years to detect the early changes in this direction. If identified it is thought possible to alter the course of the condition by applying various forms of treatment including Retina laser photocoagulation treatment.
Both BRVO and CRVO can produce a very wide range of eye problems as characterised above. In addition these conditions are also notoriously variable and dynamic – the features and prognosis can change within weeks or even years after the initial onset.