Central Retinal Vein Occlusion ?

Retina (back part of the eye) receives its blood supply through a single artery and vein called central retinal artery and vein respectively. This artery and vein can get blocked in some patients similar to stroke seen in brain or heart. This blockage could be in one of the branches (Branch retinal vein occlusion, BRVO) or may block the central vein itself (Central retinal vein occlusion, CRVO). Any blockage in the central retinal vein blocks the exit path of blood leading to a scenario similar to a traffic jam. Due to this blockage, the vein becomes dilated and eventually may rupture leading to bleeding and swelling. This swelling gets collected at the center of retina called macula causing macular edema. This macular edema leads to decreased vision.

CRVO develops from a blood clot or decreased blood flow in the central retina vein. CRVO can be caused by multiple factors. Age is the most important risk factor. The other risk factors associated with CRVO are Hypertension, Diabetes, Smoking, Glaucoma (Raised eye pressure) etc. The specific cause for the clot to form is unknown.

There is no significant link between hereditary factors and CRVO. However, certain hereditary diseases like thrombophilia, spherocytosis, sickle cell disease increase the risk of CRVO.

CRVO is one of the leading retinal vascular diseases causing decreased vision after diabetic retinopathy. It is commonly seen in patients with risk factors like hypertension, smoking, diabetes and old age. If one eye develops CRVO then the risk of other eye also developing CRVO is 6 – 17 %.

CRVO causes sudden decrease in vision. The severity of vision loss depends on the type of CRVO and extent of swelling of retina. There are 2 types of CRVO: i] Non Ischemic CRVO (81%): The vision loss in this type is reversible with treatment. 5% patients may improve without treatment also however majority will worsen without adequate treatment. If it is not treated for many months, the edema may cause degenerative changes in retina leading to permanent decrease in vision. With treatment patients with non ischemic CRVO generally show significant vision improvement. ii] Ischemic CRVO (19%): This is the more serious variant of CRVO where the vision is very poor with less chance for improvement even with treatment. The rate of complications are also higher in this type.

CRVO patients have sudden drop in vision. It needs prompt retinal evaluation and treatment by retina specialist. However, it is not an emergency where we need to treat it immediately the same day. A prompt evaluation and treatment helps limit the damage to eye.

The acute signs resolve over 6 - 12 months with disc collateral and pigmentary changes at macula as residual changes. In some patients (more commonly in Ischemic type) long term complications in the form of neovascularisation with secondary glaucoma may develop. In acute stage, patient may need frequent follow ups and treatment.

CRVO generally presents as sudden painless decrease in vision in the acute stage. Some patients may have distorted / wavy vision where objects appear distorted. Occasionally patients may complain of painful red eye if neovascular glaucoma has developed due to ischemic CRVO / inadequate treatment or follow up. Pain in CRVO generally happens only in the later stages as a result of complication (Neovascularisation) secondary to CRVO. Therefore, it is important to have regular follow up to identify and treat these complications at an early stage and prevent severe pain and blindness. CRVO can cause headache if ocular pressure increases as a result of neovascular glaucoma.

CRVO can be diagnosed clinically with the presence of retinal bleeding, swelling in the retina and dilated and tortuous vessels. OCT helps to assess the extent of swelling of retina and also treatment response. FFA is occasionally required to look for ischemic CRVO.

CRVO is like a stroke of the eye where the blood vessel in the retina gets occluded partially or completely. It is important to identify the cause for this blockage so as to prevent the stroke in other eye or elsewhere in the body. Therefore, systemic workup in the form of blood tests like CBC, blood sugar, lipid profile, homocysteine levels is essential to identify the underlying pathology.

To answer the first question there is no fixed number of injections that are required. Each patient responds differently and the number of injections depends on how the eye responds to treatment. The treatment is to be continued till the patient shows visual improvement with reduction in swelling. I generally give an estimate of 3-4 injections as most patients need 3-4 injections to stabilize. However, some patient may need fewer injections and some patients may need more. The injections are usually given on 1 month intervals. The injection is given inside the white part of the eye and is not painful. You can resume your daily activities immediately following the injection with no additional restrictions post injection, no admission required.

To answer the second question, the aim of treatment is to decrease the swelling in the retina. Usually patients show good improvement in vision with treatment with some patients regaining near normal vision back. However, in ischemic CRVO the patient may not have significant improvement in vision with treatment and thus may need treatment to be stopped. Rarely, some patients show improvement in the initial stage of treatment but then do not improve further with treatment due to conversion of non ischemic to ischemic CRVO.

In patients who do not undergo adequate treatment or do not follow up regularly as advised, secondary complications may develop in the form of neovascularization. In such patients laser therapy may be required in addition to intravitreal injection.

There is no cure for the occlusion in CRVO. Unlike in other strokes, we cannot lyse or remove the clot as the blood vessels in the retina are very narrow. The treatment is primarily aimed at preventing vision loss and treating any complications that may arise.

Optimal control of known risk factors and systemic diseases may reduce the incidence of CRVO. There is some evidence that controlling ocular pressure can also lead to decreased chance of CRVO.