Central Vein Occlusion
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- What is a Central Retinal Vein Occlusion?
A central retinal vein occlusion (CRVO) is when blood flow leaving the eye is blocked and the blood backs up into the retina. Imagine your bathtub – a clog in the drain causes water from the faucet to fill faster than it can leave and soon the tub is overfilled with water – this is similar to a CRVO. The retina lines the back wall of the eye. It is responsible for receiving light from the outside world and sending the light image to the brain. The retina needs nutrients and oxygen to survive, it receives these through a central retinal artery. When the retina is done feeding on nutrients and oxygen, the remainder is brought out of the eye by the central retinal vein. The vein and artery share space at the back of the eye. The vein is softer than the artery – so when the space gets tight from glaucoma, high blood pressure or having thick blood – the vein collapses, a clot forms, and blood can no longer drain from the eye.
- Who is at risk for having a Central Retinal Vein Occlusion?
Patients with high blood pressure, glaucoma, diabetes and more rare conditions that cause thick blood like multiple myeloma. Often, patients develop CRVO without having risk factors.
- What causes a Central Retinal Vein Occlusion?
As the central retinal vein collapses, blood flow slows down, more blood sticks to the wall of the vein, eventually becoming a clot, and preventing any blood to drain from the retina. As this occurs, the blood backs up into the retina filling the normally dry retina with fluid and expanding it like a sponge. A wet retina does not work normally and this causes vision to worsen. Sometimes blood backs up so much that there is no room for fresh blood carrying oxygen and nutrients. Without their proper nutrients these areas of retina may die.
- How is a Central Retinal Vein Occlusion diagnosed?
Usually someone notices blurry vision in one eye that can develop over one to several days. There can be a wide range in vision loss, from a subtle fogging of the vision, to severe vision loss where someone may only be able to appreciate a hand moving close to their face. Sometimes a patient may go to the general eye doctor to see if new glasses help, but this type of vision loss does not improve with glasses. Examination of the retina with specialized lights and lenses after dilation of the pupils can discover signs of CRVO. Computerized photographic tests such as a fluorescein angiogram (FA) and optical coherence tomography (OCT) help in evaluating the blood vessels and assessing the amount of fluid that has accumulated in the retina. An FA is done by injecting an orange dye into a vein of the arm and taking special digital photographs of the dye as it flows through the blood vessels in the retina to look for abnormalities. An OCT is a painless computerized scan of the retina that provides a detailed view of the inner retinal structures.
- What can be done for a Central Retinal Vein Occlusion?
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In areas of retina that have been damaged due to lack of nutrients and oxygen, laser can be applied to prevent further damage. Historically, lasers have been used more frequently, but with the success of injectable steroids and anti-VEGFs, lasers have had a more secondary role. For vision that is reduced because of fluid accumulation, anti-VEGF medications can be used to help fluid reabsorb. Anti-VEGF medications were developed to remove VEGF (Vascular Endothelial Growth Factor), a major factor in making blood vessels leaky. These medications must be delivered as an injection in the eye after anesthetic and antiseptic treatment to the eye to make the injection as comfortable and safe as possible. Since the introduction of anti-VEGF medications, many clinical trials have proven their efficacy. Results show that 2 out of 3 patients with fluid in the retina can have visual gains with monthly injections. Bevacizumab (Avastin), Ranibizumab (Lucentis), and Aflibercept (Eylea) are the most useful Anti-VEGF drugs we have available today. In addition, a longer acting dexamethasone steroid implant (Ozurdex) has been found to be helpful in improving vision. Your retinal consultant will help decide which medicine is right for you.
- How frequently do I need Injections?
The Anti-VEGF agents currently available last for 4-6 weeks before their effects fade and a new injection is typically needed. The steroid implants may last even longer. Most clinical trials show that treatment every 4-8 weeks gives the best results. Some patients need more frequent injections and others need less frequent injections. The intervals required by any one patient may change with time. Your doctor will decide with you how frequently you need treatment.
- Does the injection hurt?
The procedure is quick and practically pain free for most patients. A sterile lid speculum helps keep the eye open and an antiseptic kills any germs. It is common for the eye to feel irritated and scratchy for a day after the injection. Worsening vision and severe pain, especially if it is not improving after the first day may be signs of an infection after an eye injection and if you have these symptoms you must contact your doctor.
- Will I go blind from Central Retinal Vein Occlusion?
There is a wide range in visual outcomes for patients with CRVO and the final visual outcome cannot be predicted. In general the worse the vision is after the initial occurrence, the worse the prognosis. In eyes where the nutrient and oxygen flow has been disrupted there is a higher likelihood of severe vision loss. However if the nutrient and oxygen flow is not severely disrupted, more than half of patients can expect an improvement in vision with time. That said, almost certainly the vision will not be the same compared to before the CRVO.