Diseases
Overview
Age-Related Macular Degeneration
Diabetic Retinopathy
Retinal Vein and Artery Occlusions
Flashes of Light and Floaters
Retinal Tears and Retinal Detachments
Macular Pucker (Epiretinal Membrane)
Macular Hole
Vitreomacular Traction
Uveitis (Inflammation in the Eye)

Retinal Vein and Artery Occlusions

Retina Vascular Occlusions

What is a Retinal Vascular Occlusion?
The retinal blood supply comes from a central artery and vein that enter and exit the eye along with the optic nerve. At this point, the vessels begin to branch out to provide nutrition for the entire retina. As the result of systemic diseases, these vessels can be damaged and pre-disposed to becoming occluded. The vessels can be blocked as they enter the eye, called a central occlusion, or along one of the smaller branches.
 
What are the symptoms of a Vascular Occlusion?
When a retinal vessel becomes occluded, the area of the retina that is supplied by the vessel will be damaged and will cause the vision to decrease. When the blockage affects the vessels in the center of the retina, the macula, the vision loss is most significant. The onset is typically sudden or noticed upon awakening, is painless, and can worsen over several days. If severe, abnormal blood vessels may form and cause bleeding in the eye that may cause floaters in the vision or high eye pressure that may cause pain.
 
How is a Vascular Occlusion diagnosed?
The most importance part of making the diagnosis of a vascular occlusion is a thorough examination of the retina through a dilated pupil. To aid in the diagnosis, a scan of the retina is typically performed with Optical Coherence Tomography (OCT), this allows the retina to be seen in cross-section to better evaluate any retinal damage. The OCT scan can also be used to follow the response to treatment by creating detailed measurements of the retina. Another important diagnostic test is Fluorescein Angiogram (FA), which allows the visualization of blood flow through the retina and can evaluate the full extent of the blockage and for the presence of leakage and abnormal blood vessels. Many different retinal diseases can present as fluid or blood in the retina and it is important to have a complete exam by an experienced Retina Specialist to ensure the correct diagnosis and treatment. 

Fluorescein angiogram of retinal vein occlusion shows disruption of the normal blood flow

Retinal Vein Occlusions

How do Retinal Vein Occlusions form?
The retinal veins collect the blood after it has transferred the oxygen and nutrients to the retina and returns it to the systemic circulation. These vessels become blocked due to a clot, or thrombus, forming and preventing flow. Branch retinal veins will occlude at points where they cross the retinal arteries, at these points the vein narrows allowing a clot to form. The central retinal vein will occluded as the vein exits the eye with the optic nerve, there is a constriction at this point and can predispose to clot formation. When the flow of blood through a vein becomes obstructed, the resulting backup causes leaking fluid, bleeding, and poor blood flow. Each of these components can cause vision damage and while fluid and blood can resorb, poor blood flow causes permanent tissue damage. The amount of poor blood flow, or ischemia, determines the visual prognosis.

On examination, blood leaks from the damaged veins into the retina

What are the risk factors for Vein Occlusions?
The damage to retinal vessels is the same damage that occurs to vessels in the brain and heart that lead to heart attack and stroke. The major risk factors are the systemic medical problems hypertension, diabetes mellitus, hyperlipidemia, and smoking. It is very important to work with a Primary Care Doctor or Internist to control systemic factors to minimize risk.

How is a Retinal Vein Occlusion treated?
Treatment for BRVO and CRVO are similar and involves controlling the leakage from the damaged blood vessels that leads to edema and limiting development of abnormal blood vessels as the retina tries to heal.

Controlling Edema
The leakage from the damaged vessels is driven by inflammation and a molecule that is secreted as a result of the tissue damage, vascular endothelial growth factor (VEGF). To combat this, an antibody is injected into the eye by Intravitreal Injection to bind the VEGF molecule and prevent it from stimulating vessel leakage; these medications are known as antiVEGF compounds. There are 3 currently available drugs in this class; 
  1. Ranibizumab (Lucentis) – FDA approved for the treatment of retinal vein occlusion.

  2. Aflibercept (Eylea) – FDA approved for the treatment of retinal vein occlusion.

  3. Bevacizumab (Avastin) – Most commonly used medication but not FDA approved for the treatment of retinal vein occlusion. 

Using these medications the leakage can be controlled to improve the vision loss associated with the fluid buildup.
 
Inflammation also plays a role in the blood vessel leakage and, when the edema is not controlled with antiVEGF compounds, steroids may be used. These steroids can be given beside the eye or inside the eye. Triamcinolone is the most commonly used steroid but lasts for a shorter time than a dexamethasone implant (Ozurdex) that can last up to 3 months. The side-effects of steroids include glaucoma and cataract formation which will be monitored and treated if occur.
 

Any medication used to treat edema is temporary and will need to be repeated as long as the damaged veins continue to leak. Treatments and examinations will be individualized and repeated as necessary until the condition stabilizes.
 

Controlling Neovascularization
As the retina tries to heal, abnormal blood vessels, or neovascularization, can develop in an attempt to restore blood flow to areas of ischemic retina. These blood vessels can grow along the retina, optic nerve, or in the front of the eye along the iris. If the vessels grow along the retina or optic nerve they can lead to bleeding that fills the eye and blocks the vision, known as a vitreous hemorrhage. These vessels can also lead to the development of scar tissue that can pull on the retina and cause retinal detachment. If the blood vessels grow along the iris, the fluid drainage system of the eye can be blocked and lead to elevated eye pressure, known as neovascular glaucoma. Often the elevation can be very sudden and severe resulting in sudden decreased vision and pain. To control these vessels, laser photocoagulation by Pan Retinal Photocoagulation (PRP) is needed to treat the areas of retina that are ischemic. The laser burns the retina and stops it from producing signals that drive the neovascularization. Sometimes, an antiVEGF medication is given prior to the laser to control the neovascularization temporarily until laser can be applied. After the retina is treated, the blood vessels will stabilize and regress. In patients with neovascular glaucoma, the eye pressure can normalize but if too much scarring has taken place then the eye pressure may require surgery with a glaucoma specialist.


Retinal Artery Occlusions

How do Retinal Arterial Occlusions form?
The retinal arterial supply comes from a branch of the ophthalmic artery that comes from the carotid artery. Arteries carry blood rich in oxygen and nutrients to the retinal tissue. Retinal arteries are susceptible to blockages from debris in the bloodstream (ie. Embolus), or due to inflammation of the vessel walls.
 
Emboli are small particles of debris in the bloodstream that can come from many sources. In the retinal circulation, emboli are most frequently from carotid artery plaques or from the heart. The carotid artery develops plaques in the walls of the vessel as a result of long-term hypertension, hyperlipidemia, and smoking. These plaques can obstruct blood flow as well as rupture and send small cholesterol particles down the circulation that can be large enough to block the central retinal artery or a branch retinal artery. Emboli from the heart most commonly come from the mitral and aortic heart valves. These valves can be damaged by a congenital abnormality, inflammation, or infection. When debris develops on the surface, the motion of the valve can send particles through the circulation.
The retina become pale when the normal arterial blood flow is blocked

Fluorescein angiogram after retinal artery occlusion shows very poor blood flow to the retina

What are the symptoms of a Retinal Arterial Occlusion?
When retinal arteries are blocked temporarily there can be a transient loss of vision known as amaurosis fugax.  The vision undergoes a generalized darkening, graying, or blackening and then returns to normal as the blockage resolves and the retina is again perfused with oxygen and nutrients. If the blockage does not resolve, permanent tissue damage can occur after as little as 90 minutes without blood flow. When the central retinal artery is occluded the entire vision will be affected, and a branch artery will affect only the portion of the vision that is supplied by that area of retina. After an episode of poor blood flow to the retina from an arterial occlusion the vision loss is permanent and is typically very severe.
 
How is a Retinal Arterial Occlusion treated?
Treatments are limited in their effectiveness since permanent damage occurs very quickly after the start of symptoms. It is very important to be evaluated for the cause of the arterial blockage to minimize the risk of further vascular events. Ultrasonography of the carotid artery and an echocardiogram are potential studies that are needed to evaluate for the potential cause. Certain blood tests may also be needed to evaluate for a serious systemic inflammation or a clotting disorder. If any positive test result, it is very important to be evaluated for potential treatment. Modifying the risk factors of smoking, hypertension, and hyperlipidemia are essential in reducing the risk of arterial blockage in the other eye and stroke.
 
What other complications can come from Retinal Arterial Occlusions?
After the initial event, the retina will break down the blockage and blood flow will be restored to the retina, at least in part. However, the vision typically does not improve.  As the eye tries to heal there can be the development of abnormal blood vessels in the retina or in the front of the eye in the iris. This complication needs to be monitored for as it can cause additional damage to the retina and the eye. If abnormal vessels develop, laser photocoagulation treatment is necessary to prevent their continued growth.
 
 
Dr Kruti Dajee Dr Jawad Qureshi Dr Johnathan Warminski