While there are similarities in how they occur, the clinical nature of these two events have unique properties, management and out come.
Branch Retinal Vein Occlusion
A branch retinal vein occlusion is essentially 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, eventually 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. The occlusion site determines the extent or distribution of the hemorrhage, ranging from a small branch veins giving rise to a quadranic occlusion involving one fourth of the retina to a hemispheric (hemi-retinal) occlusion involving one half of the retina (see left photo) to an occlusion of the central retinal vein, which involves the entire retina (when the central vein is involved, this is called a central retinal vein occlusion which is discussed below).
Branch retinal vein occlusions are by far the most common cause of retinal vascular occlusive disease. Males and females are affected equally. Most occlusions occur after age 50, although younger patients are sometimes seen with this disorder (in this age group it is often called (papillophlebitis). The highest rate of occurrence is in individuals in their 60’s and 70’s.
These disorders are similar to those for vascular occlusive disease elsewhere in the body such as stroke and coronary artery disease. Specifically, aging, high blood pressure, diabetes, and smoking are all risk factors. It is very important to find out if there is an underlying cause to any vascular occlusive disease. This office will refer patients to their internist or Family practice physicians for the appropriate medical testing and evaluations.
Risk factors for Branch vein occlusion
Testing for Venous Occlusive Disease:
- CBC with differential
- Lipid profile/Sickle analysis in African American
- Fasting blood glucose
- Blood pressure
- SED rate with C reactive protein
- Prothrombin time/partial thromboplastin
- HIV if suspected
- Lyme filter if suspected
- Fasting plasma hemosycteine level
- Chest X-ray
The diagnosis of a retinal branch vein occlusion can be detected by your eye care provider who will see dilated blood vessels, hemorrhages, and swelling (edema) in the distribution of the vein. It appears that the more complete the blockage, the more intense the hemorrhages and the edema. In fact, the blockage may be so dramatic that the involved capillaries cease to function and close off blood supply to areas of the retina, we call the ischemia or capillary non-perfusion. About 10% of patients suffering from a branch vein occlusion will experience a branch or a central vein occlusion in the fellow eye in the future. Therefore as stated above, it is very important to perform the proper tests to determine if there is an underlying treatable cause.
There are three complications of branch retinal vein occlusion which threaten vision:
- Macular edema.
- Macular ischemia or non-perfusion (lack of blood supply).
- Neovascularization (growth of new abnormal blood vessels).
When the distribution of the vein involves the center of the retina (macula), bleeding and fluid leakage occure, producing symptoms. Leakage in the macula causes macular edema in which a patient will have blurred vision and loss of portions of the field of vision (corresponding to the distribution of the obstructed vein). Basically, the edema damages the architecture of the retina, causing these symptoms. These visual changes can be monitored with an Amsler grid. A fluorescein angiogram is a useful test in evaluating macular edema and determining whether treatment with laser is necessary (see below).
In the first three to six months after the occurrence of the branch vein occlusion, there is often significant hemorrhaging that involves the macula, making it difficult to predict the clinical course and visual outcome. After the first few months, it may be useful to do a fluorescein angiogram. This test is helpful in analyzing the retinal vessels, particularly the capillaries which may manifest abnormalities such as leakage or macular ischemia (non-perfusion: closure of blood vessels which supply the retina with oxygen and other nutrients). If the fluorescein angiogram indicates that capillary non-perfusion is the cause of the vision loss, it is unlikely that the vision will improve significantly over time on its own. However, 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.
The most devastating potential problem in vein occlusion is that of neovascularization. Neovascularization can be responsible for two kinds of problems:
- Neovascular Glaucoma
- Vitreous Hemorrhage
In advanced cases, where there is significant closure of capillaries, abnormal vessels may grow (neovascularization) and lead to bleeds into the overlying ocular cavity known as the vitreous (vitreous hemorrhage). In severe cases of neovascularization and subsequent bleeding, retinal detachment can occur from pulling by these vessels on the retina (traction detachment). Laser photocoagulation treatment is 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 usually 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.
There is no known medical treatment for retinal branch vein occlusion. Anti-coagulants such as heparin, coumadin and aspirin have not been shown to be of value in preventing branch vein occlusion or managing its complications. Because anti-coagulants may be associated with systemic complications, they are prescribed only in specific clinical circumstances, for example for patients with known clotting abnormalities.
Central Retinal Vein Occlusion
Central retinal vein occlusion is closure of the final retinal vein (located at the optic nerve) which collects all of the blood after it passes through the capillaries. The systemic risk factors for branch retinal vein occlusion mentioned above are also risk factors for central retinal vein occlusion.
Central retinal vein occlusion is generally categorized into two forms:
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 Ischemic or non-perfusion. This Ischemic group is predisposed to a peculiar type of neovascularization that occurs in front of the eye on the iris (rubeosis irides). These eyes may develop a very high pressure known as neovascular glaucoma due to obstruction of the fluid outflow channels (see right thumbnail). This is a very serious complication which is associated with severe vision loss and may cause pain and loss of the eye itself. Laser photocoagulation treatment is useful in managing rubeosis irides or neovascular glaucoma. If performed early in the course (when iris neovascularization is first detected), it may help prevent these complications. Patients with recent central retinal vein occlusions must be followed monthly in order to detect this complication in a timely manner.
Less frequently than in branch vein occlusion, patients with central retinal vein occlusion, may also develop neovascularization in the back of the eye, causing vitreous hemorrhage and retinal detachment. Laser treatment may be useful in managing these complications.
As with branch retinal vein occlusion, macular edema and non-perfusion are frequently seen with central retinal vein occlusion. Macular edema, even without significant macular ischemia (lack of blood supply), is not treated routinely with laser photocoagulation. This is because a recent study failed to show a benefit for patients with central retinal vein occlusion, particularly for those who are elderly. (In contrast, laser treatment has been shown to be effective for patients with branch retinal vein occlusion). It is possible, but not proven, that some young patients with central vein occlusion of the non-ischemic type may benefit from localized laser treatment for macular edema.
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 (Branch and Central retinal vein occlusion) have a thorough medical work-up as outlined previously.
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. Some investigators have had good results with this approach while others have not yet confirmed its efficacy and safety.
In summary, 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. Some of the complications of retinal vein occlusion may be appropriately managed with laser treatment. It is hoped that through further research, even better strategies for prevention and management will be developed.
Please note that much of the above content was provided compliments of: Vitreous-Retina-Macular Consultants New York