Retinal Vascular Occlusion
When a blood vessel in the retina becomes occluded, it can lead to serious and sudden vision loss. The treatment options and prognosis depend on which type of blood vessel becomes occluded and the severity of the obstruction.
Retina vein occlusion vs retinal artery occlusion
It is important to differentiate whether it is the retinal artery or vein that is blocked because the treatment is different as well as the causes.
Retinal vein occlusion. The retinal vein are vessels that carry the blood out of the eye, after it rich oxygen supply has been utilized in the capillary beds by the cells and tissues. A blockage in the vein is called a retinal vein occlusion.
Retinal artery occlusion. The artery carries freshly oxygenated blood into the eye and an obstruction in these vessels are often due to a piece of plaque that has broken off in the heart valve or carotid artery and travels to the retina and lodges in a small vessel. This prevents the tissue from receiving vital oxygen and blood and leads to sudden, painless loss of vision. Currently, unfortunately, there is no proven method to improve vision once it is lost. Immediate diagnosis and treatment similar to sudden onset stroke can in some cases, reduce the degree of vision loss, but this needs to be addressed within several hours of the onset of the condition, and requires going to the emergency room for stroke work up.
Other treatments such as hyperbaric chamber or trying to reduce the intraocular pressure have yielded benefit in sporadic cases but have not been proven, reliable, nor reproducible in most patients.
Treatment for central retinal vein occlusion
Central retinal vein occlusion
When the large main vein, called the central retinal vein, becomes occluded it can lead to serious obstruction that prevents used blood from exiting the eye. This blockage creates back pressure, like in a plumbing system, and the cascading effects causes stasis of the blood flow. The intravascular pressure and damage caused by lack of normal blood flow damages the vessels causing bleeding into the tissue (retinal hemorrhage) as well as swelling due to fluid build up (retinal edema). Since old blood cannot exit the eye, and the blood circulation is slowed down significantly, new fresh blood carrying oxygen also cannot get in to supply the nutrients that the retina needs. This oxygen deprivation is called ischemia, and it causes damage to the photoreceptors, the cells responsible for vision. Severe and prolonged ischemia leads to irreversible damage and loss of vision.
The causes of CRVO, or central vein occlusion, are not clearly understood, but there are conditions that have been strongly associated with it. Systemic medical conditions that cause a tendency to damage blood vessels, cause vascular inflammation, cause blood clots to develop, and alter the normal blood coagulation process, including some medications, as well as smoking are risk factors. High blood pressure, diabetes, hormonal contraceptive medications, hereditary blood clotting abnormalities, auto immune diseases, hematological protein abnormalities, and unknown (idiopathic) are associated with CRVO.
Treatment for CRVO is based on the risk factors, as well as retinal diagnostic test results and examination. First line treatment is usually a medication that is injected (intravitreal injection) into the middle of the eye cavity that is filled with a gelatinous fluid (vitreous). The medication then targets certain molecules and cells to reduce inflammation and swelling. In some cases, laser photocoagulation may be necessary to reduce risk of recurrent bleeding that causes vision loss (vitreous hemorrhage). In more severe cases, where the cloudy vision does not improve due to vitreous hemorrhage, a surgery may be necessary (vitrectomy) to help regain vision.
Most patients with CRVO will need ongoing treatment to control the central swelling of the retina (macular edema) that causes the vision to become obscured. Treatment helps to improve the edema, but as it is not a cure, additional treatment is necessary to maintain the best possible vision in light of the injury and damage caused by the condition.
Treatment for branch retinal vein occlusion (or tributary vein occlusion)
BRVO, branch retinal vein occlusion or Tributary retinal vein occlusion
When a vein other than the main (central) vein is occluded, it is called a branch retinal vein (a smaller tributary vein. The mechanism of occlusion is thought to be different than the central retinal vein occlusion in that instead of a blood clot or fibrin blocking the main vein, the blockage involves a retinal artery that has hardened (arteriosclerosis) that crosses over the vein causing compression as well as causing a fibrin and blood clot to develop.
The risk factors for BRVO are similar to those for CRVO, as well as the management. In general, BRVO carries a better prognosis for vision than CRVO, since a smaller area or region of the retina is affected by the ischemia instead of all of the retina. Milder forms of the condition have better long-term visual prognosis and in some cases after initial treatment, it may stabilize enough to not warrant additional treatments. In moderate to severe cases, however, treatment for macular edema is necessary to maintain the best vision possible if recurrent edema is present.