Retinal vein occlusions are commonly seen in most eye care offices. They are second only to diabetic retinopathy as a cause of visual loss due to retinal vascular disease. Retinal vein occlusions develop from obstruction of the venous outflow from the eye. The blockage may vary in size and location, accounting for a wide range of retinal outcomes. There are two main forms of retinal vein occlusion: branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO). While there are similarities in how they occur, the clinical nature of these two events have unique properties, management, and outcome.
If a patient develops an occlusion of the central vein in both eyes, there is a greater possibility of an underlying systemic cause. It is recommended that all patients involved with one of the venous occlusive diseases (BRVO or CRVO) have a thorough medical work-up.
A branch retinal vein occlusion is a blockage of the portion of the circulation that drains the retina of blood. The arteries deliver blood to the retina. The red blood cells and plasma then course through the capillaries and eventually into the venous system, reaching the central retinal vein.
With blockage of any vein, there is back-up pressure in the capillaries, which leads to hemorrhaging and fluid leakage on the retina. Usually, the occlusion occurs at a site where an artery and vein cross. Typically, the artery crosses over the vein so that any hardening of the artery compresses the vein (which has a thinner wall). When the distribution of the vein involves the center of the retina (macula), bleeding and fluid leakage occur, producing symptoms.
- Macular edema
- Blurred vision
- Loss of portions of their field of vision (corresponding to the distribution of the obstructed vein)
- Neovascularization (which can be responsible for neovascular glaucoma or vitreous hemorrhage
- In severe cases of neovascularization and subsequent bleeding, retinal detachment can occur
Branch retinal vein occlusions are by far the most common cause of retinal vascular occlusive disease.
Central retinal vein occlusion is closure of the central retinal vein (located at the optic nerve) which collects all of the blood after it passes through the capillaries. Central retinal vein occlusion is generally categorized into two forms based on the amount of blockage: non-ischemic (perfused) and ischemic (non-perfused).
This means that some central retinal vein occlusions are associated with a significant enough obstruction of capillaries to cause areas with no blood supply. This is called an ischemic or non-perfused CRVO. These patients are predisposed to abnormal vessel growth called neovascularization. This is felt to occur when cells release a protein called vascular endothelial growth factor (VEGF) in an attempt to restore circulation. If vessel growth on the iris occurs (rubeosis iridis), these eyes may develop a very high pressure known as neovascular glaucoma due to obstruction of the fluid outflow channels. This is a very serious complication which is associated with severe vision loss and may cause pain and loss of the eye itself.
Less frequently than in branch vein occlusion, patients with central retinal vein occlusion may develop neovascularization in the back of the eye, causing vitreous hemorrhage and retinal detachment. As with branch retinal vein occlusion, macular edema and non-perfusion are frequently seen with central retinal vein occlusion.
There are no known medical treatments for retinal branch vein occlusion. Treatments only address symptoms and may help prevent listed complications.
Treatment options include:
- Observation and Management
- Photocoagulation Laser Therapy
- Intraocular Injections
Modifying risk factors associated with this condition can help lower or reduce a patient’s chance of acquiring this condition.
Risk factors for branch vein occlusion (BRVO) and central retinal vein occlusion (CRVO)
- Hyperviscosity syndromes
- Diabetes mellitus
- Cardiovascular disease
- Carotid artery obstruction
- Optic nerve drusen
- Cavernous sinus fistula
If the poor vision is due to edema or swelling, laser photocoagulation is very useful in sealing leaking capillaries to enhance resolution of the edema for stabilization and improvement of the vision. Sometimes in venous occlusive disease, scar tissue can form on the surface of the retina. This condition, which is called a macular pucker or an epiretinal membrane may result in distorted vision (metamorphopsia) which is not improved with laser treatment.
Laser photocoagulation treatment is also very useful in preventing neovascular glaucoma and stabilizing vitreous hemorrhage. Indeed, laser treatment can cause stabilization or, at times, regression of the vascular growth. This treatment, while important in helping to prevent further visual loss, is not associated with improvement in vision. The neovascularization may develop in 40% of those cases where branch vein occlusions produce large areas of capillary non-perfusion. This retinal neovascularization generally develops in the first 6 to 12 months after the occlusion. Unless laser treatment is performed, at least 60% of the patients with neovascularization will experience episodes of vitreous hemorrhage and or neovascular glaucoma.
Intravitreal Kenalog (steroid)
Within the past couple of years, interest in injecting a steroid, triamcinolone (Kenalog), has received much interest. After topical anesthetic, some lidocaine is administered followed by Kenalog that is injected directly into the vitreous cavity. Patients are seen monthly for intraocular pressure monitoring, and repeat injections may be needed after 4 months.
Avastin is an anti-cancer drug which binds to and inactivates vascular edoothelial growth factor (VEGF). Because this is found in elevated levels in patients with ischemic retinal vein occlusions, it is occasionally used in the treatment. Since this is an off-label use of the drug and is not consistently covered by insurance, only some patients will elect this treatment. For now, it is probably best given in additional to standard therapy or in some cases when standard therapy fails.
Vitrectomy with intravenous tissue plasminogen activator (tPA)
One surgical approach, pioneered by Dr. Jeffrey Weiss in Ft. Lauderdale, Florida, is to perform a vitrectomy followed by cannulation of a major retinal vein and injection of tPA (tissue plasminogen activator). Similar to its use in stroke patients, this clot-dissolving solution is used early in the course of the disease to attempt to relieve the obstruction and to allow restoration of blood flow.
Vitrectomy with radial optic neurotomy
Another approach, pioneered by Dr. Mitch Opremcak in Columbus, Ohio, is a standard vitrectomy followed by a radial incision in the optic nerve to decompress the nerve at the site of the venous obstruction.
Recently, a new, investigative approach to the treatment of central retinal vein occlusion has been introduced. This is the creation by laser of a communication between the retinal circulation and the circulation behind it (choroidal circulation) so that the obstructed venous blood can pass out of the eye through this other circulation. A select few investigators have had good results with this approach, while most have not yet confirmed its efficacy and safety.