Retinal Venous Occlusion

CRVO (Central Retinal Venous Occlusion) and BRVO (Branch Retinal Venous Occlusion) are retinal diseases caused by outflow obstruction of blood, out of the retina. The resultant increased tissue pressure causes haemorrhages (bleeding) and retinal oedema (water-logging). The degree of ischaemia (or absence of blood circulation) can be variable and worse in CRVO as the entire venous drainage is impeded.

The two complications that can happen as a result are macular involvement (resulting in visual loss) and neovascularisation (abnormal blood vessels causing either bleeding inside the eye resulting in sudden and dramatic visual loss or significantly increased eye pressure causing pain and leading to Glaucoma).

Investigations

Retinal venous occlusion is a vascular disease. Eye involvement draws attention to the state of the vasculature all over the body. Blood pressure measurement and blood tests therefore form the first line of investigation for this condition. Smoking cessation is a major modifiable risk factor. Other modifiable risk factors should be addressed by a combination of diet, lifestyle changes and medication.

Eye Investigations

Apart from the tests associated with a comprehensive clinical examination to identify vascular risk factors like raised blood sugar or blood fats, eye investigations that may be required to make a decision to treat or monitor therapy are:

Ocular Coherence Tomography (OCT)

OCT is a relatively new technology that has changed the landscape of retinal investigation in the recent years. It is a non invasive imaging modality that uses a special light to scan the layers of the retina and finds its use in the management of Glaucoma, AMD, diabetic retinopathy and other macular diseases. The images take only a few minutes to acquire and the latest generation of OCT machines offer unsurpassed 3-D resolution to accurately identify the anatomy at different layers inside the human retina.

Fundus Fluorescence Angiography (FFA)

FFA has been around for a few decades providing valuable information for retinal specialist on the blood circulation of the retina. It involves an injection of a fluorescent dye through a vein in the arm. Within a few seconds the dye enters the general circulation of the body including the retinal circulation. Photographs of the retina are taken using special filters in rapid sequence, so that the blood vessels are observed as they fill up with the dye. Upon evaluating the series of photographs, your consultant is able to identify abnormal vessels as in AMD, leakage from vessels or absence of circulation in conditions such as diabetes or retinal vein occlusion.

From a patient’s perspective, the photographs would be taken for 5-10 minutes following the injection. They are then asked to be seated for a further hour for observation. The cannula that had been inserted into the vein for the purpose of injecting the drug, would then be removed and the patient sent off home.

Fluorescein also colours the skin (often with a lovely tan!) which fades away over a few days. Fluorescein is excreted by the kidneys and patients are asked not to be concerned to see a change in the colour (a bright yellow) of their urine for a few days afterwards as it is one of the ways by which the dye leaves the body. It is quite a safe drug although as with any drug that is being injected into the body it can be allergic to some people. A transient nauseating feeling is common and rarely patients experience a more severe allergic response. Although is possible in theory, a serious anaphylactic reaction resulting in death has not been observed in one large reported series of 100,000 patients who had FFA.

Treatments

Argon laser macular photocoagulation treatment has been shown to be beneficial by BVOS (Branch Vein Occlusion Study, 1984) for macular oedema due to BRVO. However it has a very limited role in CRVO.

Since then, two intravitreal therapies, Lucentis (anti-VEGF agent) and Ozurdex(steroid) have been licenced for use in macular oedema due to both CRVO and BRVO. Intravitreal therapies are administered via injections into the eyeball. Robust clinical trials (BRAVO, CRUISE, GENEVA) have shown their efficacy. Patients who have BRVO tend to do better when compared to CRVO. NICE has recommended the use of Ozurdex and Lucentis for patients who are not suitable for laser photocoagulation. The choice of agent that would be appropriate is a clinical decision that needs to be individualised. It is worth remembering that the degree of ischaemia as a result of the vascular event often dictates the extent of visual recovery with these treatments as they only address the oedema but not re-perfuse the retina. Lucentis is adminstered monthly to begin with followed by as-and-when-required schedule depending on the recurrence of oedema. Ozurdex is administered six monthly.

The treatment for neovascularisation is Argon laser scatter photocoagulation.

External Resources

Royal National Institute of Blind people (RNIB)

RNIB is a leading UK charity founded in 1824 and their website is the largest source of information available on the internet on blindness and partial sightedness. They also run a useful helpline.
http://www.rnib.org.uk/eyehealth/eyeconditions/eyecondi…