Dr Ben Wild
Overview |
Our vision comes from light waves stimulating retinal photoreceptors and these photoreceptors transferring their signals through a multitude of other cells to the ganglion nerve cells then to the brain. To help keep these photoreceptors healthy, there are 2 sources of blood flow. One is behind the eye located in the choroid and the other is inside the eye either resting on or inside the retina. Both of these sources represent very strong blood vessels that help create the blood-retinal barrier.
A frontal view of a healthy retina.
A retinal vein occlusion occurs when one of the veins that extends into the eye is blocked. This usually occurs due to health conditions that cause arteries to thicken (atherosclerosis) which leads to veins being compresses at cross over points. When a vein is blocked, the pressure inside the vessel increases, blood flow stops, and the retina may become oxygen deprived (hypoxic). Fluid then starts to leak into the retina.
A frontal view of a retina with a central retinal vein occlusion (top) showing a swollen optic nerve and retinal hemorrhaging all over and a branch retinal vein occlusion (bottom) where the vein is occluded by an artery crossing overtop, retinal hemorrhages are noticed and the vein is white.
If the blockage occurs inside the optic nerve it is called a central retinal vein occlusion (CRVO) and affects the entire field of view, if it occurs in a vein on the retina it is called a branch retinal vein occlusion (BRVO) and affects only the part of the visual field corresponding to where the vein was occluded. If blood flow is completely stopped, the vein occlusion is deemed ischemic, and if it is partially blocked, it is deemed non-ischemic.
Signs and Symptoms |
Signs
CRVO | Absent or mild effect on pupil reactivity, dilated veins, bleeding in the retina, cotton wool spots in the retina (indicating lack of oxygen), swollen retina, swollen optic nerve. |
BRVO | Dilated veins, bleeding in the retina, cotton wool spots in the retina (indicating lack of oxygen), may see plaque in the vein, swollen retina. |
Symptoms
CRVO | Sudden painless vision loss, black/dark red spots in vision. |
BRVO | Often no symptoms, sometimes sudden painless blurred and/or distorted vision, black/dark red spots in vision. |
Causes and Risk Factors |
Causes
Blocked retinal vein.
Risk Factors
Age (over 65), high blood pressure, high cholesterol, diabetes, glaucoma/elevated eye pressure, oral contraceptives, smoking, dehydration, kidney failure, inflammatory autoimmune disease.
Prevention and Treatment |
Prevention
Avoid all cardiovascular risk factors (high blood pressure, diabetes, etc.), avoid smoking, avoid oral contraception.
Treatments
· Monitor the eye while doing a full stroke work up including blood pressure testing, blood viscosity testing, complete blood count, random glucose, and cholesterol. If this occurs multiple times or in both eyes, also include chest x-ray, homocysteine levels, rheumatoid factor, anti-nuclear antigen, carotid artery imaging, adenosine, angiotensin-converting enzyme, and antineutrophilic cytoplasmic antibody.
· If vision is worse than 20/30
o Anti-VEGF injections.
o Steroid injections or implant.
· If blood vessels grow into the retina
o Same as above
o Laser photocoagulation.
Prognosis |
If there is an ischemic (total blockage) CRVO, the possibility of full recovery is low due to the high likelihood of macular degeneration, glaucoma and/or optic nerve damage in. Non-ischemic CRVOs often resolve on their own within 6-12 months sometimes with permanent retinal bleeding and blood vessel scarring but usually do not affect long-term vision.
Ischemic and non-ischemic BRVOs resolve on their own within 6-12 months, however, the retina does experience oxygen deprivation for several weeks or months. This can stimulate the growth of blood vessels (neovascularization) into the retina and/or iris and cause glaucoma 3 months after the vein occlusion in 8% of cases.