What are retinal vein occlusions?
Retinal vein occlusions are blockages to the vein component of the retinal blood circulation. The blockage is usually associated with atheromatous hardening of an adjacent artery, which disrupts the flow of blood, setting up conditions predisposing to a thrombosis in the vein. Low flow causes the pressure in the veins to increase, which therefore leak fluid and bleed into the surrounding retina.
How do retinal vein occlusions affect my vision?
The vision is affected by:
i) blood overlying the retina
ii) fluid within the retina
iii) retinal ischaemia.
Retinal ischaemia means poor blood supply to the retina, which being complex neural tissue like the brain, requires adequate nutrition and oxygenation. When the venous drainage of the eye is blocked, the blood flow of the whole circulatory system, including the arterial retinal supply, is reduced. Just as in the brain, when disruption of the arterial supply causes a stroke, so to in the eye, when disruption to the arterial supply to the retina, causes loss of function (ie reduced vision).
What is the prognosis?
Retinal vein occlusions are amongst the worst things that can happen to the eye. The prognosis is very much related to age and extent/location of the vein occlusion. In patients under the age of 60, 95% of the vision may well recover, but I am afraid that in older patients, the prognosis is poor. While the vision may be affected by only a limited extent initially, usually further events occur over a period ot 18 months to 2 years which progressively impair vision at each stage. Branch retinal vein occlusions have a better prognosis than hemispheric or central retinal vein occlusions and only the latter are associated with the devastating late complication of neo-vascular glaucoma.
Is their any treatment?
Of the three causes of visual impairment noted above, haemorrhage will disperse without treatment over a period of about 18 months. Unforunately, there is no treatment for retinal ischaemia, so this leaves retinal oedema as the only area where treatment might be directed. Studies have shown that treatment of macular oedema in patients with branch retinal vein occlusions to be worthwhile and this can be undertaken either with argon photocoagulation laser or with intravitreally injections of triamcinolone. Recently, several publications have suggested that 2 to 3 injections of avastin, if given from 6 weeks to 4 months after the event, may be associated with better long-term visual acuites. Injections of avastin and triamcinolone are certainly more effective than laser in the early weeks after the onset of a retinal vein occlusion, when the view of the retina is obscured by blood. Unfortunately, in the presence of retinal ischaemia, treatment of retinal oedema is unrewarding. Nevertheless, an increasing number of my patients have been hugely helped with avastin injections. Most have needed 3 injections, although unfortunately one or two seem to need ongoing treatment
Why have I developed a retinal vein occlusion?
Most patients with retinal vein occlusions have a history of either high blood pressure or diabetes. In patients under the age of 50, especially in those with vein occlusions in both eyes, there may be problems with blood clotting and we would organise a thrombophilia screen. Having said this, I have yet to see a patient with an abnomral thrombophilia screen.
What is the risk of both eyes being affected?
Fortunately, only one is affected in most patients and in those with two eyes affected, one is usually only affected to a limited extent.
What are the long-term complications?
i) recurrent haemorrhages
A small proportion of patients with branch retinal vein occlusions develop fine new blood vessels growing forward from the retinal surface into the vitreous. These can bleed and blur the vision for a few weeks until the blood disperses. We would usually undertake some argon laser photocoagulation in these patient as a first step, in order to close down the vessels. In a proportion of patients, the vitreous gel can pull on the blood vessels and cause recurrent bleeding. These usually do well with a vitrectomy, when the vitreous tugging on the blood vessel is mechanically removed.
ii) neovascular glaucoma
This is the dread complication of a central retinal vein occlusion and classically occurs after 100 days. In practice, however, this may occur up to 2 years after the event and is the reason why we follow you up for some time afterwards. It is more likely to occur in badly affected patients with poor vision and can theoretically be prevented and to some extent treated with argon laser photocoagulation. A lot of burns are required, however, and this may have to be delivered in more than one treatment session.
Recently, some patients have been treated to good effect with one of the anti-VEGF drugs such as Avastin. I have started to use this in my patients and have noticed a remarkable improvement. Avastin injections are particularly useful when the view of the back of the eye is obscured which would make laser impossible.