Retinal Vein Occlusions
The body’s circulatory system relies on arteries and veins. Arteries carry oxygenated blood and nutrients to various parts of the body, while veins carry used-up blood back to the heart. A vein occlusion is when an obstruction occurs in one of these veins, preventing the circulation system from functioning properly and removing waste. When this occurs in the retina, it is referred to as retinal vein occlusion. This blockage creates a backup in the system, resulting in the leakage of blood and plasma into the retinal tissue.
If the blockage occurs in the main vein leaving the eye through the optic nerve, this is known as a central retinal vein occlusion (CRVO). If one of the branches is blocked, this is called a branch retinal vein occlusion (BRVO). Retinal vein occlusions can cause retinal bleeding (hemorrhage) and swelling (edema), which can lead to significant visual loss. In addition, disruption of the blood supply can permanently damage the retinal tissue, due to a lack of oxygen and nutrition. This may result in the development of abnormal blood vessels as a response to the lack of oxygen.
Retinal vein occlusions typically occur in individuals greater than 50 years old, with men more likely to develop them. Sometimes, individuals with this condition are found to have blood clotting disorders or inflammatory conditions. The second eye is affected in approximately 10% of cases. Common risk factors for retinal vein occlusions include:
- Being overweight or obese; having an increased body mass index (BMI)
- Cardiovascular disease, including having uncontrolled high blood pressure, especially among senior patients
- High cholesterol
- Narrowing of the carotid artery
- Other eye conditions, such as glaucoma (high pressure in the eye), macular edema, or vitreous hemorrhage
- Raised intraocular pressure (IOP) has been shown to raise CRVO risks.
As retinal vein occlusion risks increase with age, older people have a greater likelihood, with more than 90% of cases affecting those over the age of 55 years. However, younger people may develop BRVOs, particularly those with blood clotting issues. It’s been shown that 25% of younger patients (under 50 years) develop CRVOs due to hypertension. Among younger women, there may be an association between taking the oral contraceptive pill and retinal vein occlusion development.
Clinical Appearance & Symptoms
As mentioned, retinal vein occlusions are classified as central retinal vein occlusion (CRVO) or branch retinal vein occlusion (BRVO). When patients have a retinal vein occlusion, they frequently complain of blurred vision, distortion, and/or a central blind spot. Occluded veins typically appear tortuous, like a hose twisting when water flow is blocked. There is bleeding seen in the distribution of the blocked vein in BRVO; the whole retina is involved in CRVO. You may also experience retinal swelling in the same distribution; macular edema is a common finding and is often a source of significant visual loss.
When there is a severe blockage, in which blood flow is cut off or significantly reduced, sensitive retinal tissue can become permanently damaged, in a process called ischemia. As a response to ischemia, the eye may develop abnormal new blood vessels called neovascularization. These new vessels are fragile and tend to bleed, potentially resulting in vitreous hemorrhage. They may also scar and pull on the retina, which may lead to traction retinal detachment. If these blood vessels grow in the drainage structure of the eye, a very serious form of glaucoma can develop called neovascular glaucoma.
When a retinal vein occlusion is suspected, certain diagnostic tests may be requested by your retinal specialist. Their purpose is to confirm the diagnosis, evaluate the severity of the blockage, and possibly guide treatment. Fluorescein angiography may be employed in the diagnosis of retinal vein occlusion. In this procedure, a dye is injected into an arm vein, which travels through the circulatory system to the eye. The dye acts as a tracer and is photographed as it passes through the ocular circulation, allowing the blockage site to be clearly identified. Dye leakage is also often seen from macular edema and areas of neovascularization, and ischemic areas can be identified and measured.
Optical coherence tomography (OCT) is commonly used to obtain a high-resolution image of the retina and any associated macular edema. This technique is very valuable in quantifying the degree of fluid and monitoring response to potential treatment.
A retinal vein occlusion is incurable, and most often, your ophthalmologist will advise that you properly manage any contributing, underlying conditions and risk factors, like high blood pressure or cardiovascular disease. In the event treatment is necessary, they focus on macular edema and the complications of neovascularization, with the goal of sealing any leaking blood vessels.
In regard to macular edema, this may be treated in two ways. For BRVO specifically, laser treatment has been shown to be effective in reducing retinal swelling and improving vision. However, this benefit has not been found for CRVO.
A newer treatment, medications injected into the vitreous cavity (see sections on “Intravitreal Injection” and “New Medications”), has been found to benefit macular edema. While currently experimental, it may help to stop abnormal blood vessel growth by inhibiting the responsible protein, thereby relieving macular edema and restoring vision. Current medications being injected include a corticosteroid (Kenalog) and an anti-neovascular agent (Avastin).
Generally, retinal vein occlusion patients who only have macular edema tend to do well. While the injections are effective, you’ll have to continue them for several years until the blood vessels have repaired themselves. However, should macular blood vessel loss develop, permanent vision loss may occur.
Complications of neovascularization include bleeding from abnormal blood vessels and a severe form of glaucoma, called neovascular glaucoma. At their earliest signs, your retinal specialist will recommend a different laser treatment, known as pan-retinal photocoagulation, to target the abnormal vessels. It may also help prevent any complications, which can cause blindness, and even result in the loss of an eye in the worst cases. Regardless of the treatment option, it’s vital to properly manage any related conditions, such as macular edema and glaucoma.
Recovery and Success Rates
The prognosis for retinal vein occlusion may depend on age, as younger patients have been found to have better outcomes. Among older patients, research shows that one-third improve without treatment, one-third stay the same, and one-third get worse. For central retinal vein occlusions, if ischemia hasn’t occurred, a return to “baseline” or “near baseline” vision occurs in about 50% of patients. “Baseline” refers to an earlier measurement of a condition compared to a later one, to compare for changes.
Chronic macular edema is usually poor vision’s main cause, with the prognosis generally correlating with initial visual acuity, the eye’s ability to distinguish details of objects at a given distance.
- If visual acuity is 20/60 or better, it’s likely to remain the same.
- If the patient has 20/80-20/200 vision, visual acuity may improve, stay the same, or worsen.
- In visual acuity worse than 20/200, improvement is unlikely.
With ischemic central retinal vein occlusion, the prognosis may vary among patients. Research shows that there may be higher neovascular glaucoma risks in 50% of patients’ eyes, usually between 2-4 months.
What To Expect After Treatment
How you fare after undergoing retinal vein occlusion treatment may depend on whether you have ischemia. Patients with nonischemic central retinal vein occlusion typically have a follow-up at 3 months, although you should come in sooner you experience deteriorating vision. For those with ischemic central retinal vein occlusion, it’s recommended that you be monitored on a monthly basis for 6 months.
If you were treated with injected medications, you should be observed for a similar duration after the treatment ends, for up to 2 years. Research shows that following the injections, you can expect to double the chances of gaining 3 lines or 15 letters on an eye chart. Additionally, it’s been shown that early treatment results in greater improvement in vision.
Following injections, you may find that your eyes are initially slightly sore and/or watery, and they may be bloodshot. These symptoms are normal and should soon wear off. Until the dilating eye drops’ effects wear off, your vision will be blurred. In the event you experience a more serious eye issue, you should alert your ophthalmologist. You should also contact them if you detect changes in your condition. You’ll also need to tell your primary care doctor about your retinal vein occlusion, so they can evaluate and treat any underlying systemic illnesses.
Retinal Artery Occlusion
A retinal artery occlusion occurs when the main artery servicing the eye or one of the arteries that branch off of it becomes occluded. This blockage is typically caused by tiny blood clots, fibrin plugs, or calcific emboli. This blockage causes the eye to lose its oxygen supply, causing permanent damage to the retinal tissue with loss of vision.
Signs and symptoms
Transient loss of vision prior to the artery occlusion in some cases
- Branch Artery Occlusion: sudden & painless partial loss of vision in one eye
- Central Artery Occlusion: sudden & painless total loss of vision in one eye
Diagnosis is usually made during a complete retinal exam and is made with an ophthalmoscope and a fluorescein angiogram
Unfortunately, there are no treatment options that can restore vision that may be lost from an artery occlusion. Infrequently laser treatment may be necessary for delayed complications such as new blood vessel formation (neovascularization). Risk factors for an artery occlusion are diabetes, valvular heart disease, glaucoma, hypertension, and high cholesterol levels.