RETINAL VEIN OCCLUSION
Retinal vein occlusion, a blockage of either central or branch retinal veins, is the second leading cause of retinal blood vessel damage in North America. As a consequence of accumulated blood at the blockage, the veins burst and flood retinal cells with waste-filled blood. Various complications develop in the vitreous body as a result of the hemorrhage, or bleeding, including ischemia, or the death of cells. Over the long term, retinal vein occlusion can lead to permanent visual damage or, indirectly, blindness.
WHAT IS THE CONDITION?
Retinal vein occlusions, or the blockage of central or branch retinal veins, can occur due to two reasons. The first is the hardening of arteries, or arteriosclerosis in the arteries in contact with the veins. When a retinal artery hardens, it becomes heavier and presses against the walls of near-by retinal veins, which can eventually restrict venous blood flow. The second is the blockage of blood flow inside the veins, due to the formation of an internal wall or the coagulation of blood. Both reasons for the stoppage of venous blood flow can arise from a shared list of risk factors, including high blood pressure and cholesterol, smoking, diabetes, family history, and inheriting certain genes. Therefore, any systemic disease of the blood vessels, which can lead to the hardening of arteries or the internal blockage of venous blood flow, can directly affect the veins of the retina.
The direct consequence of a blockage forming in a branch or central retinal vein is that a large amount of blood will accumulate within the vein. Gradually, the vein’s walls will weaken against the increased pressure exerted by the growing volume of blood, and begin to leak, resulting in vitreous hemorrhage, or bleeding into the vitreous body of the eye. Vitreous hemorrhage not only blocks light from reaching the retina, it can lead to macular edema, or the swelling of retinal cells due to the absorption of blood.
The absorption of venous blood by retinal cells is a deadly problem. Cells which absorb venous blood will become poisoned by the toxicity of the waste materials in the blood. Moreover, abnormal choroidal neovascular membranes will begin to grow on the retina, and even the iris, in an attempt to transport nutrients to the poisoned cells. Because these abnormal choroidal neovascular membranes are highly fragile blood vessels, they typically worsen the existing vitreous hemorrhage by breaking/bleeding into the vitreous body. The growth of abnormal choroidal neovascular membranes on the iris may increase intraocular pressure in the eye, causing closed-angle glaucoma, which by itself can lead to complete blindness.
Depending on where the retinal vein occlusion occurs, the death of retinal cells can severely diminish a patient’s eyesight. Smaller branch retinal vein occlusions on the periphery of the retina may cause limited damage to a patient’s vision because this area is less involved in central eyesight. More harmful to a patient’s vision are branch retinal vein occlusions that are closer to the macula, since this area is responsible for central vision. The most dangerous to vision, however, is an occlusion in the central retinal vein because it can cause the death of all retinal and macular cells in very little time. In other words, the closer the retinal vein occlusion is to the central retinal vein, the more rapid its progression and damaging it will be to a patient’s vision.
BRANCH RETINAL VEIN OCCLUSION
A branch retinal vein occlusion indicates that one of the smaller branches of the retinal veins in the retina has become occluded. Generally speaking, these branch retinal vein occlusions are most commonly seen in the superior part of the retina due to the compression of the underlying vein by the overlying artery within the retina. Patients with branch retinal vein occlusion commonly notice a substantial deterioration of sight, especially if the occlustion is in the centre of their vision.
CENTRAL RETINAL VEIN OCCLUSION
The principal vein which drains blood from the retina is known as the central retina vein. Occlusion of the central retinal vein can lead to significant vision problems because all four quadrants of the retina from which the vein drains blood are affected. The spectrum of involvement of central retinal vein occlusion can, therefore, be from an incomplete central retinal vein occlusion in which there is still partial blood flow, to a complete retinal vein occlusion associated with significant ischemia, non profusion of blood vessels within the retina and substantial visual loss. This is one of the most devastating forms of retinal vein occlusion.
MACULAR BRANCH RETINAL VEIN OCCLUSION
When a small retinal vein in the macular area of the retina becomes occluded, it is known as a macular branch retinal vein occlusion. Because the macula is responsible for the central portion of vision, macular branch retinal vein occlusions have a higher likelihood of impairing in vision. The impairment in vision can be either loss of sight or distortion.
HEMI-RETINAL VEIN OCCLUSION
A Hemi Retinal Vein Occlusion refers to the condition in which half of the retinal veins inside of the eyes are occluded. Most commonly affected is either the superior half or the inferior half of the retina. Vision loss in patients who have a hemi retinal vein occlusion is, therefore, much more severe than a branch retinal vein occlusion, but less severe than a central retinal vein occlusion. It is important to note that the condition in patients with a hemi retinal vein occlusion may convert to a central retinal vein occlusion causing severe visual loss.
Reducing a patient’s systemic blood pressure may help prevent the development of retinal vein occlusions. Increased blood pressure leads to atherosclerotic changes in the arterial system, which, in the retina, can lead to the compression of the thinner walled vein in the retinal vascular system, ultimately leading to the development of a branch retinal vein occlusion. Reducing systemic cardiovascular risk factors is important to reduce the risk of retinal vein
The development of neovascularization of the anterior segment, which may significantly increase intraocular pressure, is one of the more significant problems that can develop in patients following an initial branch retinal vein occlusion, or stroke inside of the eyes. The increased intraocular pressure may lead to severe pain, visual loss, and in some instances, removal of the eye for intractable problems.
Accordingly, patients should be monitored on a regular basis, best determined by their eye care physician and based on the risks of progression. Substantial risks of progression to anterior segment neovascularization include large areas of branch retinal vein involvement or large areas of ischemia demonstrated on Fluorescein Angiography or other basic clinical findings.
Because veins are responsible for draining blood from the eye, occlusions of the retinal veins leads to congestion, which in some situations, is so severe that blood leaks out from the retinal blood vessels. This can lead to significant swelling (edema), ischemia (decreased blood flow to the eye), or the presence of blood within the retina or vitreous cavity.
The development of vitreous hemorrhage, or bleeding into the cavity of the eye, can happen in patients who have retinal vein occlusions in either early or late stages. In the early stage, the bleeding that occurs tends to be breakthrough bleeding, in which a non-excessive congestion of blood in the retina breaks through into the central vitreous cavity. Late stage bleeding can happen any time after one month of the initial episode in which severe ischemia has led to neovascularization of the retina, which subsequently bleeds into vitreous cavity. This is a much more severe condition requiring laser treatments. In those patients for whom the vitreous hemorrhage is not responding to laser, surgical intervention may be warranted.
Ischemia is a medical term used to refer to the inadequate profusion of tissues by the blood flow that is normally responsible for the delivery of oxygen and nutrients. In retinal vein occlusions, ischemia can be one of the most significant reasons for permanent visual loss following resolution of the initial swelling and blood in the retina.Ischemia can also be responsible for the development of new blood vessel growth within the retina, which can lead to vitreous hemorrhage, tractional retinal detachments, neovascularization of the anterior segments, and eventual blindness.
The early detection of ischemia using advanced diagnostic techniques including OCT, Microperimetry, and Fluorescein Angiography are essential tools that OCC Eyecare and The Canadian Centre for Advanced Eye Therapeutics have at their disposal.
Macular edema, or swelling of the retina, is one of the principal reasons for decreased vision following retinal vein occlusions. The other cause for decreased vision being macular ischemia. Edema of the retina can be managed with laser treatments, injections, and possible surgical interventions. In some patients, it is impossible to resolve edema due to the underlying ischemia, or poor blood flow, which exists in the retina, causing permanent visual loss. Some patients with chronic edema can go onto develop macular hole formations with even further loss of sight.
If the retinal vein occlusion does not extend into the central portion of vision or macula, patients may not be significantly bothered by the damage to the retina. Accordingly, it is possible for patients who have a non-macular branch retinal vein occlusion to retain substantial vision and not suffer from significant visual loss. However, even in these patients, ischemia can complicate their recovery, leading to long-term neovascularization, pre-retinal and epiretinal membrane formations, and subsequent visual loss.
In the early stages of retinal vein occlusions, there is a significant amount of intra-retinal blood in patients who have a vascular blockage. The majority of this blood will eventually reabsorb or be removed from the retina by the body itself. Despite the fact that the blood eventually resolves itself in some patients, this may take up to two years. There may be limited, or marginal, recovery of sight, since the blood itself can be toxic to the retina. Additionally, underlying ischemia, or poor blood flow to the retina, may have led to further damage. The edema which accompanies bleeding into the retina also compromises sight.
LATE NEOVASCULARIZATION OF RETINA
Following vascular occlusions within the eye, there is a considerable amount of ischemia, or decreased perfusion of nutrients and blood flow, to the retina. One of the effects of this is that the retina may develop new abnormal blood vessel growth. In a condition known as neovascularization, these new blood vessels grow into the central cavity of the retina. These weak blood vessels can bleed, scar, and detach the retina, and can also lead to neovascularization of the anterior segment. Neovascularization of the anterior segment can lead to a very devastating condition known of neovascular glaucoma, in which eye pressure becomes exceedingly elevated leading to blindness.
Because the condition can cause a variety of complications, treating retinal vein occlusions may require several different treatments, each of which targets a particular symptom of the disease. These treatments include laser pan-retinal photocoagulation, intraocular injections of Kenelog and/or the anti-VEGF drugs, Lucentis, Avastin or Eylea, pneumatic displacement, and vitrectomy surgery.
For patients who have mild edema extending into their macular region without substantial visual compromise, there may be no need for further intervention. Diagnostic testing, including Fluorescein Angiography and OCT (Optical Coherence Tomography) testing, and functional analysis using Microperimetry techniques, should be done to track progress. Monitoring these patients to see whether their visual acuity stabilizes or improves is important. Should they show further deterioration of sight however, early intervention with laser injections or surgical techniques are warranted.
LASER: PAN-RETINAL PHOTOCOAGULATION
The laser treatment pan-retinal photocoagulation uses heat to seal holes in the abnormal choroidal neovascular membranes through which blood can leak into the vitreous body. The treatment also discourages their growth by destroying dead retinal cells, but at the risk of killing healthy tissue. Possible side effects of this treatment include forming blind spots, or scotomas, and/or decreased night, peripheral, or central vision.
The use of laser in patients who have retinal vein occlusions is predominantly for three purposes:
1. Macular edema: In patients who have macular edema, or swelling of the retina, laser treatments can be used to reduce the edema. Several types of lasers are currently being used at OCC Eyecare and The Canadian Centre for Advanced Eye Therapeutics, including standard thermal lasers and newer technology Micropulse lasers, which can reduce the complications associated from higher energy thermal laser use.
2. Neovascularization of the retina: Neovascularization of the retina leads to new blood vessels growing in the retina which can ultimately lead to blindness. Pan-retinal photocoagulation can be performed on these patients.
3. Neovascularization of the anterior segment: Neovascularization of the anterior segment leads to glaucoma, which will inevitably lead to blindness. Aggressive pan-retinal photocoagulation can be helpful in reducing this blood vessel growth.
INTRAOCULAR INJECTION: ANTI-VEGF & KENELOG
Intraocular injections of Kenelog and the anti-VEGF drugs, Lucentis, Avastin, and Eylea, help decrease the growth of abnormal choroidal neovascular membranes on the retina and iris. Additionally, Kenelog can decrease macular edema by reducing inflammation due to the absorption of venous blood. All intraocular injections have the risk of causing blindness from infection and retinal detachment, among other complications.
Lucentis’ current indication includes the use in patients who have age related macular degeneration (AMD). However, due to the crossover relationship with patients who have retinal vein occlusions, it is felt that intraocular injections of Lucentis may be a beneficial therapy for patients with branch retina vein occlusion.
At the present time Avastin, a medication that is very similar to Lucentis and manufactured by the same company, has been approved for use in patients with cancer as an anti-vascular antibody. Since 2005 in the United States, the medication has been used in an off-label fashion for patients with new blood vessel growth related to wet, or advanced, AMD. The Canadian Centre for Advanced Eye Therapeutics was the first Centre in Canada to inject the medication in patients with both AMD and retinal vein occlusions. It is felt that patients who have retinal vein occlusions who go on to develop both vascular proliferation and retina edema may benefit from the use of intraocular Avastin treatment.
Kenalog, an intraocular steroid which is placed into the vitreous cavity by a direct injection, can be used in patients who have branch retinal vein occlusion to reduce the chronic edema, or swelling, in the macular region. Additionally, Kenalog can be used to reduce neovascular tissue growth should laser interventions not be helpful and surgical techniques not be warranted.
Pneumatic displacement refers to a treatment in which a gas bubble is injected into the vitreous body and positioned on the retina. The gas bubble is meant to act as a protective wall for the retina by preventing, or decreasing, the amount of blood absorbed by the retina from the vitreous body. It is an intervention to decrease retinal damage due to ischemia via vitreous hemorrhage.
The collection of intra-retinal blood in the central macular area itself can be toxic to the retina. Different techniques that displace blood include mostly surgical techniques. However, more recently, OCC Eyecare and The Canadian Centre for Advanced Eye Therapeutics have been using a C3F8 pneumatic gas bubble displacement, in which an intraocular injection of gas is placed into the eye. Coupled with face down positioning, the gas flows up, pushing on the macular region and displacing the intra-retinal hemorrhages in the central macular region. This helps to hasten recovery by both reducing edema and displacing the blood which is toxic to the retina. This research technique remains investigational and is currently being offered to patients
A vitrectomy surgery can both drain the vitreous body of blood by replacing the vitreous fluid with a clear saline solution and limit macular edema by removing the topmost layer of the retina, the internal limiting membrane. It is used in cases in which abnormal choroidal neovascular membranes are unresponsive to both laser and intraocular injection treatments. A vitrectomy surgery may also be used to perform a sheathonomy, in which the surgeon will try to directly remove or fix the retinal vein occlusion using surgery.
Vitrectomy, a surgical technique to remove the vitreous gel inside of the eyes, can be performed for branch retinal vein occlusions in three situations:
1. Persistent vitreous hemorrhage in which there has been bleeding into the eye lasting for more than six months in one year. Surgical removal of the blood can be performed, but this does nothing to treat the underlying retinal vein occlusion.
2. Chronic retinal edema: Vitrectomy surgery associated with the removal of the internal limiting membrane can help reduce macular edema in patients who have a chronic branch retinal vein occlusion which has been unresponsive to other interventions, including lasers or intraocular injections.
3. Shethotomy. Surgery to free the retinal vein occlusion following vitrectomy surgery, also known as sheathomoty, has been performed by The Canadian Centre for Advanced Eye Therapeutics. We were one of the first sites in Canada to perform this surgical intervention, which requires extensive advanced surgical techniques. However, given the availability of other, less complicated, procedures this has fallen lower in the list of interventional therapies.