Retinal Vein Occlusion


OVERVIEW

Retinal vein occlusion occurs when the circulation of a retinal vein becomes obstructed by an adjacent blood vessel, causing hemorrhages in the retina. Swelling and ischemia (lack of oxygen) of the retina as well as glaucoma are fairly common complications.

Causes and Risk Factor: The retinal vein carries blood away from the retina. When the vein is blocked, blood flow backs up and causes tiny hemorrhages, areas of swelling, and other pressure-related damage in portions of the retina that are located near the blocked blood vessels. This can cause minimal or substantial loss of vision, depending on the extent of this retinal damage. Some common risk factors for this form of retinal vessel occlusion include high blood pressure, diabetes, open-angle glaucoma, lymphoma, leukemia, multiple myeloma, syphilis and use of oral contraceptives.

There are two forms of retinal vein occlusion - Branch Retinal Occlusion and Central Retinal Occlusion

1. 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 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).

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). 


2. 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.

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. If a patient develops an occlusion of the central vein in both eyes, there is a greater possibility of an underlying systemic cause.
 

SIGNS & SYMPTOMS:

  Sudden onset
  Blurred or missing area of vision (if a branch vein is involved)
  Severe loss of central vision (if a central vein is involved)





DIAGNOSTIC TESTING:

  Retinal examination
  Visual acuity
  Slit lamp examination
  Ultrasound
  Optical Coherence Tomography
  Fluorescein Angiogram





TREATMENT:

Treatment depends on the extent of blockage:

  Partial blockage � When only a small branch of the central retinal vein is blocked, sealing the damaged area with a laser (laser photocoagulation) may improve vision.

  Total blockage � When the entire central retinal vein is blocked, there is no effective treatment. However, laser photocoagulation may be used to prevent complications, such as glaucoma.

Also being used with some positive results in the intervetral injection of a anti-VEGF medication.
 
The following are common risk factors for vein occlusion:

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