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Retinal Vein Occlusions

Introduction

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. There are two main forms of retinal vein occlusion:

  • Branch retinal vein occlusion (BRVO)
  • 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.

Branch Retinal Vein Occlusion

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, 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. Typically, the artery crosses over the vein so that any hardening of the artery compresses the vein (which has a thinner wall). The occlusion site determines the extent or distribution of the hemorrhage, ranging from a small branch veins giving rise to occlusions involving part of the retina to a hemispheric (hemi-retinal) occlusion involving one half of the retina, 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. We typically refer patients to their internist or family practice physicians if medical testing and evaluations are felt to be needed.

Risk factors for branch vein occlusion (BRVO)

  • Hypertension
  • Glaucoma
  • Hyperviscosity syndromes
  • Diabetes mellitus
  • Cardiovascular disease
  • Carotid artery obstruction
  • Leukemia
  • Optic nerve drusen
  • Cavernous sinus fistula
  • Polycythemia
  • Anemia
  • Vasculitis

Possible Testing for Venous Occlusive Disease

  • CBC with differential
  • Chemistry profile
  • Lipid profile
  • Sickle analysis in African-Americans
  • Fasting blood glucose
  • Glaucoma
  • Blood pressure
  • ESR with C-reactive protein
  • Prothrombin time/partial thromboplastin
  • HIV if suspected
  • Lyme titre if suspected
  • Fasting plasma homocystine level
  • Chest X-ray

Diagnosis

The diagnosis of a branch retinal 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 are. 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. This is called retinal 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 modify any risk factors (hypertension, lipid levels), and to perform any indicated tests to determine if there is an underlying treatable cause.

Fundus photograph of a patient with a moderate BRVO. Because the central retina (macula) is involved, there is poor vision.
Fundus photograph of a patient with a small macular BRVO. Like the patient above, the central visual acuity is poor.

Complications of Branch Retinal Vein Occlusions

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 occur, producing symptoms. Leakage in the macula causes macular edema which causes a patient to have blurred vision and loss of portions of their 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 retinal circulation and macular edema. After 3-4 months, this test is used to determine 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 bleeding 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 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 are no known medical treatments 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 central 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 based on the amount of blockage:

  • Non-ischemic (perfused)
  • Ischemic (non-perfused)
Fundus photograph of a patient with a severe CRVO. Because all flow out of the eye is severely affected, vision is extremely poor.
Fundus photograph of a patient with a mild, non-ischemic CRVO. Because some circulation remains, the central visual acuity can remain good if there is minimal macular edema.

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. Laser photocoagulation and/or freezing treatment are 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. In some patients an injection of a drug called Avastin is indicated as well. 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 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. Unlike the case with BRVO patients, macular edema, even without significant macular ischemia (lack of blood supply), is not treated with laser photocoagulation. This is because a large study failed to show a benefit for patients with central retinal vein occlusion, particularly for those who are elderly. 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 (BRVO or CRVO) have a thorough medical work-up as indicated previously.

New Treatments

Intravitreal Kenalog (steroid)

Within the past couple of years, interest in injecting a steroid, triamcinolone (Kenalog), has received much interest. After topical anesthetic, some subconjunctival lidocaine is administered. Then, 4 mg (0.1 cc) of Kenalog is injected directly into the vitreous cavity. Patients are seen monthly for intraocular pressure monitoring, and repeat injections may be needed after 4 months. While large studies have not been done, the reported responses to this procedure range from no response to dramatic improvements in vision and reduction of edema.

Avastin

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. Large clinical studies are underway. Specific information about this procedure can be found at their website http://www.crvotreatment.com

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. In his small studies, this has been associated with an improvement in circulation and vision. His office in Columbus can be contacted at 614-464-3937.

Chorioretinal anastamoses

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.

Summary

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.