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The retina is a very thin sheet of nerve tissue that lines the inside of the back of the eye. The macula, the central part of the retina, is responsible for our central vision, allowing us to read, drive and recognize faces. Much like other parts of the body, the retina and macula have both arteries and veins. The arteries transport oxygenated blood to the retina from the heart, and the veins transport blood without oxygen from the retina back to the heart. Several small veins drain blood into the larger branch retinal veins, and those four branch retinal veins then come together to form the single central retinal vein, the major vei n of the retina. Proper functioning of the retinal vessels is crucial for appropriate delivery of oxygen to the retinal tissue.
A retinal vein occlusion (RVO ) is a blockage of blood flow in one of the retinal veins. It can occur in either a branch retinal vein (branch retinal vein occlusion, or BRVO ) or in the central retinal vein (central retinal vein occlusion, or CRVO ). The occlusion causes bleeding in either one section of the retina (BRVO ) or throughout the retina (CRVO ), and can also produce swelling of the macula (macular edema). The region of the retina in which the blockage occurs will be deprived of oxygen (ischemia). In severe vein occlusions, this oxygen deprivation can even occur in the macula (macular ischemia). If a significant amount of ischemia occurs, new blood vessels may begin to grow on top of the retina (neovascularization).
Retinal vein occlusion is a major cause of vision loss in the United States and is more common in patients 65 years of age and older. BRVO is slightly more common than CRVO , and once either occurs in one eye there is approximately a 10% chance of it developing in the other eye within the next three years.
Here’s what a person with normal vision sees
This is what that same image looks like to a a person with a retinal vein occlusion
A retinal vein occlusion is usually sudden, painless, and typically occurs in only one eye at a time. Patients may notice blurring either in their central vision, in one corner of their vision or throughout their entire field of vision, depending on the location of the blockage and the resulting macular edema or ischemia, if present.
Macular edema is the most common complication and most frequent reason for vision loss resulting from RVO . In severe vein occlusions, and more commonly in CRVO , new blood vessels begin to grow on top of the retinal tissue (neovascularization). The neovascularization can result in a vitreous hemorrhage (bleeding into the clear gel that fills the back of the eye) or retinal detachment (separation of the retina from the wall of the eye).
Patients affected by a vitreous hemorrhage will usually notice a sudden increase in dark floaters. With a retinal detachment, a shadow or blind spot will present itself in a corner of the vision and may gradually enlarge to involve the central vision. Sometimes, the neovascularization occurs in the front of the eye (on the iris), causing the eye pressure to rise to a dangerously high level (neovascular glaucoma) and often resulting in the eye becoming red and painful. If untreated, neovascular glaucoma can lead to blindness.
The most common causes of RVO include:
* More common in younger patients
Aside from a dilated eye examination, the standard test to confirm the diagnosis is a fluorescein angiogram (FA ). A dye called fluorescein is injected into a vein in the arm and photographs are taken of the dye flowing through the blood vessels, allowing a retina specialist to verify the location and severity of the blocked vein.
To detect and/or confirm macular edema, the standard test used is optical coherence tomography (OCT ), a non-invasive procedure that uses an infrared light source to scan the macular tissue, which allows for an accurate measurement of the thickness of the macu la. Both tests are safely and quickly performed in the office.
Since there is no cure for either BRVO or CRVO , the focus of management is on the following:
Anti-VEGF Injections: In both BRVO and CRVO , abnormally high levels of vascular endothelial growth factor (VEGF ) occur, promoting both macular edema and neovascularization. Anti-VEGF medications that counteract VEGF are injected directly into the vitreous through the sclera (white of the eye) after numbing the eye. The medications currently being used―Eylea® (aflibercept), Lucentis® (ranibizumab) and Avastin® (bevacizumab)―are all effective in reducing the edema and improving vision. Although only Eylea and Lucentis are approved by the FDA for treatment, Avastin is commonly used “offlabel,” and all are thought to be equally safe for the eye.
One treatment approach is to start with six monthly injections and continue as needed over the next several months. Often, continued injections are needed indefinitely to maintain control of the edema. Complications are very uncommon but can include a) infection (endophthalmitis) b) retinal detachment and c) vitreous hemorrhage, all of which are related to the injection itself an d not specifically to any of the medications.
Corticosteroids: Steroids are another type of medication that can decrease macular edema. Similar to anti-VEGF medications, the steroid is injected directly into the vitreous through the sclera. Two of the most commonly used steroids are preservative-free triamcinolone acetonide suspension and Ozurdex® (a dexamethasone implant). While the entire dose of triamcinolone is injected at once, small doses of dexamethasone are released from the implant over approximately three months. The complications that result from steroid injections are similar to those of the anti-VEGF injections, but can also include the progression of cataract and the development of glaucoma.
Laser photocoagulation: Laser has been shown to be effective in improving macular edema in BRVO but not CRVO. A usually painless laser beam is directed through the pupil toward the affected region of the macula. Alone, it typically is not as effective as anti-VEGF or steroids, but laser can be helpful in combination with the above. Complications are uncommon, but can include the creation of a blind spot (scotoma).
Laser Photocoagulation: Laser is the best way to control and decrease neovascularization in either BRVO or CRVO. A stronger laser is applied to the affected region of the retina. Mild peripheral vision loss can sometimes occur. This treatment is sometimes supplemented with intravitreal injections.
If the retina specialist is unable to perform the laser treatment due to vitreous hemorrhage or retinal detachment, a vitrectomy will likely be recommended. A vitrectomy is an outpatient surgical procedure performed in an operating room that involves the removal of the vitreous from the inside back of the eye through three openings made in the sclera using a microscope and several small instruments. As with anti-VEGF or steroid injections, there is a risk of infection, cataract, retinal detachment or permanent vision loss.
Prior to any treatment, it is critical that patients have a thorough discussion with their retina specialist regarding all of the treatment options, including the risks, benefits and alternatives, prior to choosing the appropriate course of action.