Retinal vein occlusion (RVO) is a blockage in a small blood vessel that carries blood away from the retina in the eye. RVO can cause visual disturbances like blurry vision and can also lead to severe complications such as swelling or bleeding in the eye. Without treatment, it can lead to vision loss.

Overview

Retinal vein occlusion is a blockage of the small blood vessels that carry blood away from the retina in the eye, due to the formation of a clot in the blood vessel. RVO can cause vision difficulties such as blurry vision and sudden loss of vision. It is one of the most common causes of vascular abnormalities in the retina and a frequent cause of vision loss. Retinal vein occlusion is caused by an obstruction of the retinal veins by the formation of a clot (known as a thrombus). The blockage can occur in the central, hemi-central or branch retinal vein.¹ Retinal vein occlusion is the second leading cause of retinal vascular disorders worldwide.²

Types of RVO

Depending on where the obstruction occurs, RVO can be classified as central retinal vein occlusion (CRVO), hemi-retinal vein occlusion (HRVO), or branch retinal vein occlusion (BRVO).³

• Branch Retinal Vein Occlusion (BRVO): this involves blockage of one of the smaller branches of the retinal vein. This type is more common 
• Central Retinal Vein Occlusion (CRVO): this involves blockage of the main retinal vein
• Hemi-Retinal Vein Occlusion (HRVO): the blockage affects only one-half (hemiretina) of the retina. It can lead to vision loss in a portion of the visual field

Both CRVO and BRVO can be broadly classified into ischaemic and non-ischaemic, and this distinction is useful for clinical management. Non-ischemic is a mild type that causes the blood vessels in the retina to leak and ischemic is a severe type of CRVO that blocks or reduces blood flow to blood vessels in the retina.⁴

Causes and risk factors

When a clot forms in the retinal vein, blood flow is completely stopped. According to the NHS, several common medical conditions can increase the risk of retinal vein occlusion including:

• Atherosclerosis The formation of plaque (fatty deposits) in the arteries can lead to the narrowing of vessels and hence affect blood flow in the veins. Smoking and high cholesterol increase the risk of atherosclerosis
• Hypertension: high blood pressure can lead to damage in the blood vessels that can cause retinal vein occlusion
• Diabetes: uncontrolled diabetes can affect the eye and cause diabetic retinopathy. This increases the risk of developing retinal vein occlusion
• Glaucoma: increased pressure in the eye can compromise retinal vein function and increase the risk of retinal vein occlusion
• Blood disorders: conditions that increase the tendency to form blood clots, like clotting disorders increase the risk of retinal vein occlusion. Also, conditions like sickle cell anaemia and polycythaemia can block vessels causing retinal vein occlusion

Symptoms

Symptoms of retinal vein occlusion appear due to the interruption of blood flow to the retina. RVO can increase the risk of vision loss from several complications caused by interrupted blood flow to the macula. The macula is part of the retina at the back of the eye and is responsible for central vision and most of the colour vision. RVO can cause macular oedema, macular ischemia, optic neuropathy, vitreous haemorrhage, or even tractional retinal detachment. 

Symptoms from RVO can be subtle if the severity is mild or the area affected does not involve the macula. Visual field abnormalities are variably present but uncommonly symptomatic.³

Retinal vein occlusion frequently causes sudden blurriness or distortion of one eye's vision. The patient may report nonspecific symptoms of visual disturbance or noticeably worsened vision, depending on the type of RVO. Some people with RVO may perceive straight lines as wavy, a phenomenon known as metamorphopsia. In severe cases, RVO can lead to loss of vision. This vision loss will be painless.⁵

Diagnosis

Diagnosis of retinal vein occlusion can be made with the following tests:

• Eye Examination
• Optical Coherence Tomography (OCT)
• Fluorescein Angiography

Diagnosis and prognosis evaluation of retinal vein blockage requires retinal angiography, either as Optical Coherence Tomography (OCT)-based angiography or with dye injection. This makes it possible to distinguish between various RVO types. Assessing the extent and location of damage as well as the degree of ischemia is most effectively done when OCT angiographic imaging is combined with dye angiography (which can be either ICG or fluorescein). Therapy may be postponed at first since non-ischaemic retinal vein occlusions have a generally benign and self-limiting course.⁶

Management and Treatment

Since no known treatment for RVO can improve visual loss, the goal of therapy is to stop further visual loss and prevent side effects. The treatment of retinal vein occlusion (RVO) may involve various approaches, depending on the type and severity of the condition.⁷ Different treatment options include:

Medications

• Anti-VEGF injections: intravitreal injections of drugs like ranibizumab or aflibercept can reduce swelling and abnormal blood vessel growth in the retina. These drugs inhibit vascular endothelial growth factor (VEGF), which is associated with abnormal blood vessel growth
• Steroids: intravitreal or systemic corticosteroids, such as dexamethasone, may be used to reduce inflammation in certain cases
• Anti-coagulant and anti-platelet therapy: in some cases, anti-coagulant or anti-platelet medications may be prescribed to prevent further clot formation

Sometimes, central vision restoration may be possible after a course of intravitreal anti-VEGF injections or steroids. This treatment, if required, is normally recommended approximately three months after the retinal vein occlusion has occurred.

Laser therapy

• Laser photocoagulation: focal laser treatment can help seal leaking blood vessels and reduce swelling in cases of macular oedema (swelling in the centre part of the retina)
• Pan retinal photocoagulation: this approach may be used for ischemic RVO to reduce abnormal blood vessel growth

Surgery

• Vitrectomy: in severe cases with extensive bleeding and scarring, a surgical procedure called a vitrectomy may be considered to remove blood and scar tissue from the eye

Other supportive measures

• Lifestyle Modifications:
  • Smoking cessation: quitting smoking can help improve blood circulation and reduce the risk of further vascular damage
  • Blood pressure control: maintaining optimal blood pressure levels is crucial to managing RVO
  • Vision aids: low vision devices can help individuals with permanent vision loss maintain their quality of life
  • Regular monitoring: continuous evaluation by an ophthalmologist is essential to assess treatment efficacy and adjust the plan as needed

Complications

Retinal vein occlusion can lead to various complications. Visual complications associated with RVO include vitreous haemorrhage, macular oedema, macular ischemia and neovascularization.⁷

• Vitreous haemorrhage: the presence of blood in the vitreous gel (thick fluid that fills the centre of the eye) that occludes the view of the retina. There is a sudden appearance of spots or floaters in the vision and severe cases can cause complete vision loss
• Macular oedema: the macula is the central part of the retina and is responsible for central vision. Persistent swelling is a common complication that can lead to further vision impairment
• Retinal neo-vascularization: in some instances, the retina may develop new, abnormal blood vessels, which can increase the risk of severe vision loss
• Vision loss: if left untreated or inadequately managed, retinal vein occlusion can lead to permanent vision loss

People with retinal vein occlusion have different prognoses based on the type, severity, and speed of diagnosis and treatment. Compared to CRVO, BRVO often has a better prognosis, and prompt treatment can greatly enhance results. Early intervention is vital since severe occurrences of CRVO might result in irreversible vision loss.

Summary

Retinal vein occlusion (RVO) is a common eye condition that occurs when one of the veins in the retina becomes blocked, typically due to a blood clot. This obstruction can lead to a range of vision problems and is a significant cause of vision loss. RVO is most often seen in individuals over the age of 60 and is associated with various risk factors, including hypertension, diabetes, and glaucoma. RVO can have serious implications for an individual's quality of life, as it can lead to vision loss if not promptly diagnosed and managed. Diagnosis typically involves a comprehensive eye examination, including optical coherence tomography (OCT) and fluorescein angiography to assess the extent of retinal damage. The management of RVO depends on the type and severity of the occlusion, and treatments may include anti-VEGF injections, laser therapy, or surgery. These treatments aim to reduce swelling, prevent new blood vessel growth, and improve blood flow to the affected area. Early diagnosis and treatment are essential for preserving vision and preventing further complications. Regular eye check-ups and addressing underlying health conditions, such as high blood pressure and diabetes, can help reduce the risk of developing RVO.