What are the other Names for this Condition? (Also known as/Synonyms)

• BRVO (Branch Retinal Vein Occlusion)
• Central Retinal Vein Occlusion (CRVO)
• RVO (Retinal Vein Occlusion)

What is Retinal Vein Occlusion? (Definition/Background Information)

• Retinal Vein Occlusion (RVO) is defined as a blockage in the retinal vein, which drains blood away from the retina. The blockage causes blood to pool into the retinal blood vessels. This causes the walls of the vein to leak blood and excess fluid into the retina, resulting in hemorrhages (or bleeding) and edema (swelling due to leakage of fluid)
• The retina is a thin layer lining the back of the eye. It is the site where the image gets focused by the eye lens. It is made up of neurons (nerve cells) and connected to the optic nerve. Its main function is to transmit the visual stimulus it receives to the brain
• The retina is nourished by blood flow from the central retinal artery that supplies oxygen and nutrients that the nerve cells need. Conversely, the central retinal vein, takes away metabolic waste products away from the retina
• There are two types of RVO, based on where the blockage occurs:
  • Central Retinal Vein Occlusion (CRVO); if the clot occurs in the main retinal vein. CRVO may be of 2 types - ischemic or non-ischemic
  • Branch Retinal Vein Occlusion (BRVO); when the clot occurs in one or more branches of the main retinal vein
• Retinal Vein Occlusion is most common in individuals with conditions that lead to thickening of blood vessels. The risk factors include health conditions, such as diabetes, atherosclerosis, and high blood pressure, smoking habit, and certain congenital disorders
• The signs and symptoms of Retinal Vein Occlusion may include dark specks in the field of vision (called eye floaters) and partial or complete blurring of the visual field
• The condition is diagnosed on the basis of assessment of symptoms and eye examinations that include vision acuity, fluorescein angiography, and testing of the retina and macula
• There is no effective cure for most cases of Retinal Vein Occlusion. The treatment measures are aimed at delaying progression of the condition and preventing further retinal damage (such as by managing pre-existing medical conditions)
• The preventive measures for Retinal Vein Occlusion may include maintaining a good glycemic index, routine physical activity, keeping blood pressure under control, and managing one’s body weight
• The type of Retinal Vein Occlusion and the extent of its progression, prior to medical intervention, may determine the prognosis of the condition. Typically, those with non-ischemic CRVO have a better outcome than individuals with ischemic CRVO

Central Retinal Vein Occlusion is further classified into 2 types, based on whether the occlusion/blockage is complete or partial:

• Ischemic CRVO: The blood vessels are progressively closed-off, which causes the retinal tissue to be deprived of fresh blood carrying nutrients and oxygen. This in turn, triggers the formation of new blood vessels (capillaries), to seek fresh nutrients and oxygen
• Non-ischemic CRVO: It is the most common form of CRVO. It is a milder form and no ischemia and neovascularization are observed. Also, no significant complications are noted; however, the non-ischemic type can change to the ischemic type over the course of a few months to years, if left untreated

Who gets Retinal Vein Occlusion? (Age and Sex Distribution)

• Retinal Vein Occlusion is the second most common retinal cause of vision loss after diabetic retinopathy. One study reports approximately 16 million people having this condition
• The condition commonly occurs after the age of 65 years
• One eye is usually affected. However, the disease may also involve the fellow eye over time, and about 10% of individuals present with the disease in both eyes
• Some studies suggest higher prevalence of CRVO in Japanese population

What are the Risk Factors for Retinal Vein Occlusion? (Predisposing Factors)

The risk factors for Retinal Vein Occlusion may include:

• Systemic conditions:
  • Atherosclerosis: Hardening of blood vessel wall, commonly due to aging
  • Hypertension (high blood pressure)
  • Diabetes
  • Hyperlipidemia (high cholesterol can block small veins in the eye)
  • Some studies have found an increased risk of thrombosis (clots) in individuals with congenital and acquired disorders such as hyperhomocysteinemia, polycythemia, and factor V Leiden deficiency, which affect the body’s normal blood clotting mechanism and increase likelihood of developing clots.
• Ocular or eye-related factors:
  • Glaucoma (increased pressure within the eyeball)
  • Vitreous hemorrhage or hemorrhage in the fluid-filled cavity in the eye
• Other factors that include:
  • Use of oral contraceptives also increases the risk of CRVO in younger women
  • Use of diuretics
  • Using medication for low blood pressure (hypotensive drugs)
  • Smoking

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Retinal Vein Occlusion? (Etiology)

Retinal Vein Occlusion (RVO) occurs when a blood clot blocks the retinal vein. Its exact cause is unknown.

• Any factor that damages or hardens the blood vessels, or increases the viscosity of blood, or creates a turbulent blood flow can predispose one to a thrombus (blood clot). It is therefore more likely to occur in those with diabetes, high blood pressure, high cholesterol levels, or other health conditions that affect blood flow
• In some cases, hardening of the central retinal artery due to atherosclerosis may also compress the central retinal vein, as the two blood vessels are in close proximity to each other

Irrespective of the reason for clot formation, there are 2 main types of Retinal Vein Occlusion, based on where the blockage occurs:

• Branch Retinal Vein Occlusion (BRVO), when the clot occurs in one or more branches of the main retinal vein
• Central Retinal Vein Occlusion (CRVO), in which the clot occurs in the main retinal vein

CRVO is further classified into the ischemic and non-ischemic subtypes:

• Ischemic CRVO: The blood vessels are progressively occluded/obstructed, which causes the retinal tissue to be deprived of fresh blood carrying nutrients and oxygen. This in turn triggers the formation of new blood vessels (capillaries), to seek fresh nutrients and oxygen; these new vessels are called collaterals
  • The collaterals proliferate and grow over the macula (part of retina where many nerve cells converge and which is crucial to vision) and vitreous (fluid-filled cavity inside the eye)
  • However, these new vessels are friable and leaky, which causes fluid leakage and swelling in the macula (termed as macular edema), and bleeding into the vitreous. This can lead to retinal detachment
  • The new vessels also increase the intra-ocular pressure by clogging outflow of normal eye fluids, called neovascular glaucoma
  • All these changes lead to visual impairment and blindness
• Non- ischemic CRVO: It is the most common subtype of Central Retinal Vein Occlusion (around 75% of the cases)
  • It is less severe, with no ischemia and without neovascularization (new blood vessel formation) being noted
  • There are no significant complications; however, the non-ischemic type can convert to the ischemic type over the course of a few months to years if left untreated

What are the Signs and Symptoms of Retinal Vein Occlusion?

The signs and symptoms of Retinal Vein Occlusion may be subtle or obvious.

• The classic symptom is a progressive and painless loss of vision in the affected eye. This may start-off as a blurring of a part of, or whole of the visual field initially. But, it may progress to complete blindness in the affected eye in the course of a few hours to days
• Small specks, called floaters, that may be seen moving through one's field of vision. These occur mostly due to vitreous hemorrhages. When the retinal blood vessels are damaged, the retina grows new, fragile vessels that can bleed into the vitreous (the fluid that fills the center of the eye). These vessels can rupture, and the blood is seen as dark specks in the field of vision

How is Retinal Vein Occlusion Diagnosed?

The diagnosis of Retinal Vein Occlusion is undertaken through the following tests and exams:

• A general physical and eye examination that can help identify an acute and painless loss of vision in the affected eye
• An assessment of medical history, which may suggest the presence of risk factors
• Ophthalmoscopy or fundoscopy (examination of the retina after dilating the pupil) that may help reveal the following:
  • Flame-shaped or dot-and-blot hemorrhages on the retina
  • Dilated tortuous veins
  • Macular edema (swelling of area of the retina that is involved in vision)
  • Cotton wool spots (due to fluid leaking from defective blood vessels)
• Visual field testing: It will help show defects in the visual field; one’s visual acuity may be decreased
• Checking intra-ocular pressure using tonometry (it may help identify glaucoma)
• Optical coherence tomography (OCT) can show areas of macular edema by measuring thickness of the retina; this can indicate an impending CRVO
• Fluorescein angiography: A dye is injected into the arm. It travels up to the retinal blood vessels and shows if any blockages are present
• In addition, testing blood pressure, ECG, blood sugar levels, complete blood count, complete metabolic panel including urea, electrolytes, creatinine (to look for underlying renal disease), ESR, cholesterol levels etc. may also be required to check for other risk factors or systemic disease

Note: Generally, no lab investigations are needed except in bilateral eye involvement, when systemic conditions are thought to be the cause.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Retinal Vein Occlusion?

The potential complications of severe or untreated Retinal Vein Occlusion may include:

• Permanent loss of vision
• Macular edema (swelling of area of the retina that is involved in vision)
• Vitreous hemorrhage: A condition in which the new vessels formed are friable and tend to bleed
• Neovascular glaucoma: A condition in which new vessels formed increase the pressure within the eye, by clogging drainage of normal eye fluids. This may occur 3 months or more after CRVO begins

How is Retinal Vein Occlusion Treated?

Retinal Vein Occlusion is mostly incurable, because the blocked veins cannot be unblocked. The treatment is therefore aimed at preventing complications and progression of the condition, such as by preventing further blockages from taking place in the affected or unaffected eye.

The following treatment measures for RVO may be considered:

• It is important to establish the cause of obstruction/blockage, control the risk factors, and treat the underlying condition (if any present)
• Intraocular injections of anti-vascular endothelial growth factor (anti-VEGF) drugs, can help block the growth of new blood vessels, which can potentially cause glaucoma and vitreous hemorrhage
• Intraocular corticosteroid injections, to prevent inflammation which causes edema
• The intravitreal administration of certain medications may also be used to decrease macular edema
• Laser photocoagulation to reduce swelling in the retina. The aim of the procedure is to stabilize vision by sealing-off leaky blood vessels and decrease new blood vessel formation that cause impairment of macular function

Note:

• Individuals with non-ischemic CRVO should report vision deterioration immediately. Otherwise, a follow-up should be scheduled after 3 months, to look for conversion to the ischemic type
• Those with ischemic CRVO should schedule monthly follow-ups for a period ranging from 6 months to 2 years. This may help detect or avoid any significant complications from developing

How can Retinal Vein Occlusion be Prevented?

The following are some recommended preventive measures for Retinal Vein Occlusion and/or to delay disease progression:

• Ensure the control of high blood pressure
• Maintain good glycemic index by suitably managing blood sugar levels
• Increase physical exercise
• Avoid smoking
• Maintain a healthy body weight
• Some research articles have also considered the use of exogenous estrogens in postmenopausal women. However, it is always recommended to consult one’s healthcare provider on any medication use
• Getting a vision examination performed at regular intervals (every one or two years). An early detection of macular edema or abnormal blood vessels by fundoscopy is important; most patients can avoid severe vision loss, if treatment is begun before the onset of substantial damage in the eye

What is the Prognosis of Retinal Vein Occlusion? (Outcomes/Resolutions)

The prognosis of Retinal Vein Occlusion depends on the type of disorder and the extent of progression prior to medical intervention:

• About 60% of individuals with Branch Retinal Vein Occlusion may be able to retain 20/40 vision after 1 year
• In non-ischemic Central Retinal Vein Occlusion, the outcome is generally good with return of vision to normal or near normalcy in about 50% of the individuals, following treatment
• The prognosis of ischemic CRVO is extremely poor due to macular ischemia; this means that the retinal cells have died due to a lack of oxygen. The lost vision cannot be returned, and additionally, there is also a high risk for developing glaucoma

Additional and Relevant Useful Information for Retinal Vein Occlusion:

• Retinal artery occlusion is a condition wherein a blockage occurs in the arteries, which carry blood to the retina

The following link will help you understand retinal artery occlusion:

http://www.dovemed.com/diseases-conditions/retinal-artery-occlusion/