What is central retinal vein occlusion (CRVO)?
Exactly why CRVO develops is not fully understood, but there are some specific things that happen within the eye that lead to vision disturbances:
- CRVO occurs when the central retinal vein becomes blocked, or occluded, and obstructs blood flow from the eye
- The central retinal artery compresses the central retinal vein, either due to hypertension or hardening of the arteries
- Compression of the central retinal vein leads to sluggish blood flow and, eventually, blockage
- The blockage also causes proteins to be released that weaken the blood vessel and cause it to leak fluid and blood into the retina, causing swelling
Vision loss in CRVO is primarily caused by macular edema. This involves the accumulation of fluid in the center and most visually sensitive portion of the retina, known as the macula.
- Macular edema requires prompt treatment to help improve vision or slow vision loss
Description: A cross section of the eye is drawn with an arrow pointing to the blood vessels in the eye.
Narration: Retinal vein occlusion or RVO is a vascular disorder which affects the blood vessels of the retina.
Description: A picture of three older adults which goes blurry as the script mentions blurred vision.
Narration: It most commonly affects older adults and, if left untreated, RVO and its potential complications can lead to blurred vision and vision loss.
Description: A cross section of an eye zoomed in to a section showing an artery in red and a vein in blue, side by side, with arrows showing which way the blood is flowing.
Narration: There are two types of blood vessels in the eye – arteries and veins. Arteries bring oxygenated blood into the eye and veins, on the other hand, take deoxygenated blood out of the eye, back to the heart and lungs to obtain fresh oxygen.
Description: A blockage is drawn into the vein picture. Two smaller boxes are drawn: the first shows an artery putting pressure on the vein, and the second shows a blood clot in the vein.
RVO occurs when there is a blockage of a vein in the retina. This usually happens when there is pressure from a nearby artery, or if a blood clot forms in the vein.
Description: Blood and fluid are shown leaking from the vein.
Narration: When a vein is blocked, it cannot drain blood from the retina. This can lead to bleeding and leakage of fluid from the blocked blood vessels.
Description: A picture of a cross section of an eye with two zoomed in sections. The first zoomed in section shows what CRVO looks like with the main vein blocked. The second zoomed in section shows a smaller vein being blocked.
Narration: There are 2 types of RVO: In a central retinal vein occlusion or CRVO, the main vein which carries blood out of the retina is blocked. In a branch retinal vein occlusion, or BRVO, there is a blockage in one of the smaller branch veins of the retina.
Description: the picture shows how CRVO affects the whole retina and how BRVO only affects a portion of the retina
Narration: A central retinal vein occlusion affects the whole retina whereas a branch retinal vein occlusion affects only a portion of the retina.
Description: Picture showing a cross section of the eye with the macula highlighted and showing that there is distress in the macula.
Narration: RVO can reduce vision in several ways. The most common way that RVO causes vision to be reduced is through macular edema, which is swelling of the macula.
Description: Smaller pictures are drawn of a man reading, a person driving a car, two people recognizing each other, and a colourful butterfly.
Narration: The macula is the most sensitive part of the retina and it is responsible for fine, detailed vision that allows you to read, drive, see faces, and distinguish colours.
Description: Picture of a male researcher pointing to a cross-sectional picture of an eye with a close-up section showing VEGF molecules.
Narration: Researchers have shown that with macular edema there are elevated levels of a protein called Vascular Endothelial Growth Factor or VEGF in the eye.
Description: A picture of a blood vessel is drawn with new blood vessels growing from it.
Narration: VEGF is one of the signals for the body to create new blood vessels in a process called angiogenesis.
Description: A close-up of a blood vessel is drawn, showing that it is leaking and then new blood vessels are drawn which are also shown to be bleeding and leaking.
Narration: However, when present in the eye, VEGF can affect existing blood vessels making them fragile and leaky. VEGF also stimulates angiogenesis and the growth of new, weak blood vessels in the eye which can also leak and cause bleeding. This leaking of fluids leads to macular edema which can negatively affect vision if left untreated.