Retinal Vein Occlusion
The retinas in each of our eyes receive light and transmit nerve signals to the brain. They're connected to the brain by bundles of optic nerves that transmit signals to it. The brain is where that light is transformed into meaningful images. Our retinas allow us to see in conditions that range from sunrise to midnight. They distinguish wavelengths that allow us to see colours and shades of colours. They provide us with a high degree of visual clarity that allows us to pick out images as fine as the brush strokes on a Monet painting or the tiny ripples made by a mayfly on a pond.
Retinal arteries and vessels
Arteries carry blood from the heart throughout the body. The retina has one major artery carrying blood to it. In turn, veins work to return blood back to the heart where it's scrubbed and recycled. The retina has one major vein with many branches for it. When a retinal vein becomes blocked, blood isn't returned to the heart from the retina. That's known as an occlusion and commonly referred to as an eye stroke. A retinal occlusion results in bleeding and fluid leakage from the retina.
Retinal vein occlusion (RVO) is the second most common sight-threatening retinal vascular disorder after diabetic retinopathy, in one eye or the other for people 65 years of age or older. Both males and females are affected equally. Racially, Caucasians have the lowest rate of retinal vein occlusions. Some people might not even experience any symptoms of a retinal vein occlusion at all. Others might suffer severe visual impairment. Common underlying causes for retinal vein occlusions include:
- Hardening of the arteries
- High blood pressure
- Increased pressure from glaucoma
- Leakage of fluid into the macula known as macular edema
- Blood clotting disorders
- Tobacco use
- high cholesterol
- people over the age of 60
Types of retinal vein occlusions
There are two types of retinal vein occlusions. Those are branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO). BVROs typically affect 50 percent or less of the retina. They're most often found where an artery and a vein cross. Studies suggest that a hardened artery can cause a blood vessel to rupture and result in a CRVO. A serious CRVO might affect the entire retina.
Branch retinal vein occlusion (BRVO)
BRVOs are far more common than CRVOs (0.5% - 2% in age> 65). A major, minor or peripheral branch retinal vein might become occluded without any pain at all. The victim might experience blurred vision, distorted images, an altitudinal defect or blind spots. Retinal examination might reveal an arc of hemorrhages like the arc of a football on a long pass to a receiver or that of a shooting star. These arcs provide a doctor with a strong basis for a diagnosis of a BRVO.
Central retinal vein occlusion (CRVO)
CRVOs are fairly rare (0.1 - 0.2% in age > 65). As opposed to BRVOs, CRVOs could be accompanied by considerable pain too. They have been categorized as non-ischemic and ischemic. An ischemic CRVO is a far more serious condition that can result in severe visual impairment. An ischemic condition will cut off the blood supply needed to keep tissue alive and cause a sudden loss of vision in one eye. Victims might not be able to see light or even count fingers in front of them. Most CRVO patients will have hardening of the arteries, high blood pressure, chronic glaucoma or diabetes. A non-ischemic CRVO isn't as dangerous, and it might not continue to get worse over time. The prognosis for a person with a non-ischemic CRVO is usually good to very good.
Diagnosis of BRVO and CRVO
BRVOs and CRVOs are best diagnosed by dilating a patient's pupils. By doing so, the examining doctor can get a good look at the retina. Any occlusions are easy for the trained eye to see and diagnose. Other tests might involve a fluorescein angiogram where a small amount of dye is injected into the arm. Once that dye travels to the eye, the central and branch blood vessels are readily apparent. Another diagnostic test is optical coherence tomography that uses light waves to take images of the retina in cross-sections.
Treatment of BRVO
Every case of BRVO is different. About 50 percent of all patients with a BRVO aren't even treated. An eye doctor might only tell a patient that the condition could require a period of frequent observation and monitoring as often as every two weeks for three to six months. With other patients, BRVOs can cause a degenerative condition, and central vision might be lost as a result irreparable scarring.
There is no cure for a BRVO. The treatment objectives are to manage the disorder, maintain vision stability by sealing leaking retinal abnormal new blood vessels that results in another condition called neovascularization. These new vessels can leak blood and fluid into the vitreous gel that fills the inside of the eye. This can result in the "floaters" that we sometimes see. In cases with severe neovascularization, the retina could be caused to detach from the back of the eye.
Some patients can't be treated after a BRVO due to the severity of the damage to the blood supply to the retina. If neovascularization develops, it might call for a laser treatment called sectoral panretinal photocoagulation. That procedure might be less effective than other alternatives. The procedure protects the affected eye against any other sudden vision damage that might result from bleeding into the eye's vitreous gel which raises other issues. Steroid implants have also shown promise, but they only last four to six months and must be repeated over a minimum course of two to three years. With steroids, the risk of cataracts increases as does the risk of steroid induced glaucoma.
Like BRVO, there's no cure for CRVO either, so the sooner that a CRVO has been diagnosed and treated, the lower the chances of having more severe damage done to an eye. Individuals who begin CRVO treatment within two weeks to a month after the occlusion event have the best chances for a favorable outcome. Blood and fluid from a CRVO build up in the macula which is the area of the retina that provides the sharpest vision. When that occurs, sight can become distorted. That condition is known as macular edema. It's the most common cause of vision loss for people with a CRVO. That's why doctors target the macula for treatment after a CRVO. At this point in time, treatment with anti-angiogenic and anti-vascular endothelial growth factor-A (VEGF-A) like Avastin, Lucentis or Eylea in the eye appear to be very promising. They target the proteins that stimulate growth of leaking eye vessels. They are also known to have frequently reversed the symptoms of CRVO and the macular edema that results from it. In certain cases, these medications have actually reversed loss of vision by inhibiting the growth of new blood vessels, diminishing leakage and preventing bleeding.
Reducing the risks for BRVO and CRVO
There are certain things that you can do on your own to reduce the risks of BRVO and CRVO. Maintaining your blood pressure, cholesterol levels and weight are important. Eating a low fat diet and regular exercise will help keep those under control. Follow your doctor's instructions and take any prescription medications as recommended. If you believe that you've suffered a BRVO or CRVO, get to an emergency department right away, and follow up on a timely basis with the doctor who the emergency department physician refers you to. Time is of the essence with these conditions. The sooner you treat for either BRVO or CRVO, the better opportunity you will have for saving at least some of your sight if not all of it.