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Central retinal vein occlusion

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Patients with retinal vein occlusions usually present with a sudden painless loss of vision in one eye. 

 

Retinal vein blockage leads to hemorrhaging, damage of the retinal vessels, and ischemia.

With vein occlusion, the cause of the vision loss is due to damage of the vasculature, which ultimately leads to ischemia.

Ischemia causes areas of the retina to become nonfunctional due to a lack of nutrient supply, leadingto permanent loss of vision.

Edema results from leakage of fluid from the involved vasculature,and is another cause of vision loss.

The edema fluid causes separation of the retinal layers, which causes vision loss.

The most common conditions associated with retinal vein occlusions include hypertension, diabetes, increased body mass index, generalized systemic vascular disease, glaucoma, autoimmune and inflammatory conditions, and clotting disorders. 

If edema occurs within the macula, decrease in vision can be significant.

 

Retinal vein occlusion is divided into 3 types:central retinal vein occlusion (CRVO), hemiretinal vein occlusion (HRVO), and branch retinal vein occlusion (BRVO). 

 

HRVO (hemiretinal retinal vein occlusion) has a worse prognosis than BRVO but a better prognosis than CRVO. 

 

Occlusion at the lamina cribrosa of either the superior portion or the inferior portion of the central retinal vein, causes  an HRVO.

 

HRVO’s pathophysiology is similar to that of CRVO but is managed similarly to BRVO. 

HRVO prognosis is determined by the initial visual acuity and macular involvement. 

The incidence of these conditions is low,  yet they can have devastating visual complications.

 

 

The prevalence of CRVO as 0.1% and of BRVO as 0.6% of the population.

 

Retinal vein occlusions cause stasis of blood drainage within the eye. 

 

When a vein occlusion occurs, it causes stasis of blood drainage within the eye. 

 

The stasis often results from thrombus formation due to an artery compressing a vein. 

 

 

Retinal vein stasis often results from thrombus formation due to an artery compressing a vein. 

Usually seen in adults over the age of 50 years.

A common cause of vision loss in older individuals.

Retinal vein occlusion is the second most common retinal vascular disorder after diabetic retinopathy.

Estimated 16 million individuals affected worldwide.

If left untreated can lead to vision impairment or blindness.

Incidence 520 new cases per 1 million annually.

Risk increases with age, typically occurring in patients older than 50 years.

Common associations of retinal occlusions include:  hypertension, diabetes, increased body mass index, generalized systemic vascular disease, glaucoma, autoimmune and inflammatory conditions, and  blood clotting disorders. 

 

Less macular involvement results in a better visual acuity and a better prognosis.

Only 20% of eyes are predisposed for an HRVO, as veins draining the inferior and superior portions of the retina need to merge posterior to the lamina cribrosa and then form the central retinal vein. 

 

 

Retinal occlusions should be categorized as to whether they are ischemic or non-ischemic

Two types of retinal vein occlusion occur, branch retinal vein occlusion and central retinal vein occlusion.

Progression from a nonischemic to ischemic CRVO within the first 4 months occurs in 15% of cases, and a 34% chance of this occurring within 3 years.

 

 

Ischemic CRVO  presents with unilateral sudden painless loss of vision, and acuity levels will be reduced to worse than 20/200. 

 

All retinal vein occlusions can present major risks including:  neovascular glaucoma, retinal detachment and a vitreous hemorrhage if rupture of preretinal neovascularization occurs.

 

Appearance of the retina on funduscopic examination:

A CRVO has multiple hemorrhages across the retina, cotton wool spots if there is ischemia, optic disc edema, and retinal nerve fiber layer damage.

An HRVO has an appearance similar to that of a CRVO.

Nonischemic CRVO will have less-severe fundus findings described as hemorrhages in all quadrants, and vessel tortuosity but only mild dilation of the retinal vessels. 

Ischemic CRVO has severe hemorrhaging across the retina with retinal edema, and moderate to severe venous dilation with tortuosity and cotton wool spots.

With long-standing CRVO, neovascularization of the iris, optic disc, or retina may be present.

 

If the occlusion occurs in smaller veins of the retina, it is referred to as a BRVO, and vision loss may be less extensive. 

 

If the occlusion occurs in larger veins, such as the central retinal vein, vision loss is often devastating and widespread, because the whole retina is involved. 

BRVO signs include superficial hemorrhages, cotton wool spots if there is ischemia, dilated tortuous veins, and potential retinal edema. 

With long-standing BRVO neovascularization of the iris, optic disc, or retina may be seen.

 

Determining the classification of a CRVO as ischemic significantly changes the treatment.

CRVO is one of the primary causes of sudden unilateral painless vision loss in adults. 

The initial visual acuity after occurrence of the CRVO determines prognosis.

Ischemic CRVO has a more guarded prognosis and may develop neovascularization: there is a 50% chance of developing neovascularization of the iris, which often leads to neovascular glaucoma.

A CRVO may occur due to the compression of the central retinal artery on the central retinal vein, as they share a common sheath of adventitia. 

 

This predisposes the vein to compression from the artery with diabetes and hypertension. 

This leads to thrombus formation and causes blockage of blood outflow, leading to stasis. 

This in turn causes damage to vessels within the retina and can lead to hemorrhaging.

 

Retinal assessment reveals retinal vessel tortuosity with dilated vessels, and dot/blot hemorrhages will be present along with flame-shaped hemorrhages in all 4 quadrants. 

Some areas of nonperfusion presenting as cotton wool spots may be present.

Ischemic CRVO have a poor prognosis due to the ischemia within the macula. 

Ischemic CRVO typically do not show improvement and need to be monitored for neovascularization. 

Neovascularization can manifest at the optic nerve, retina, and on the iris, causing neovascular glaucoma. 

Neovascular glaucoma occurs in the first 2 to 5 months after initial presentation but may occur any time over a 2-year period.

It is important to distinguish between non-ischemic and ischemic CRVO based on their different prognoses.

 

The 2 tests that  differentiate ischemic from non ischemic : are pupil testing and electroretinography (ERG). 

Vein  occlusion is likely ischemic if the patient presents with a relative afferent pupillary defect (Marcus Gunn pupil) and has reduced amplitude of the B wave on electroretinography.

Branch retinal vein occlusion occurs at an arteriovenous intersection.

Branch retinal vein occlusion is four times more common than central retinal brain inclusion.

Branch retinal vein occlusion is more frequent in men than women.

The origin of the occlusion and its effects depends on the area of occlusion: occlusion  in smaller veins of the retina, it is referred to as a BRVO, and vision loss may be less extensive. 

 

 

Occlusion  in larger veins, such as the central retinal vein, vision loss is often devastating and widespread, because the whole retina is involved. 

 

Retinal vein occlusions cause loss of vision as a result of damage to the vasculature, which ultimately leads to ischemia.

Ischemia in the retina causes it to become non-functional due to a lack of nutrient supply and leads to permanent loss of vision.

The 5 year incidence of branch retinal vein occlusion is 0.6% and at 15 years is 1.8%.

Branch retinal vein occlusion is present in 1 of 2 locations: superotemporal (66%) or inferotemporal (30%), and in 7% the opposite eye can be involved within 4 years.

BRVO has a better prognosis then CRVO., as approximately 50% to 60% of eyes that have a BRVO will return to an acuity level of 20/40 or better. 

 

 

BRVO’s prognosis is determined by acuity level. 

 

 

If macular involvement is present, the prognosis is worse, as with at least 5 disc diameters of retinal ischemia: there is a 36% chance of developing neovascularization of the disc or retina. 

 

 

2% of eyes with a BRVO, are associated with neovascularization of the iris.

 

 

BRVO often results from arteriosclerosis of the retinal arteries due to hypertension. 

 

 

Arteriosclerosis can cause compression of veins from arteries at crossing points in the retina due to their common adventitial sheath.

 

 

A thrombus can occur at that crossing point, causing a BRVO. 

In branch retinal vein occlusion the process can be benign with approcximately 55% having visual acuity of 20/40 or better without treatment.

In branch retinal vein occlusioncomplications of macular edema and neovascularization can appear, in 60% and 255 of cases, respectively.

In central retinal vein occlusion, the occlusion is at or proximal to the lamina cribosa of the optic nerve.

Central retinal vein occlusion occurs where the vein exits the eye.

While less frequent than In branch retinal vein occlusion. it can be more severe, witha greater risk of serious complications and visual impairment.

Incidence of central retinal vein occlusion is 8 per 10,000 per year.

Central retinal vein occlusion causes can be local such as glaucoma and/or systemic such as hypercoagulation.

Additional risk factors for central retinal vein occlusion include glaucoma as elevated intraocular pressure may compromise retinal vein outflow.

The second most common retinal vascular disease after diabetic retinopathy.

Prevalence 1-2% and individuals older than 40 years of age( Mitchell P et al).

In a population-based study the 10 year incidence of retinal vein occlusion was 1.6% (Cugati S et al).

Affects 16 million people worldwide(Rogers S et al.).

 

RVO risk factors: hypertension, smoking, increased body mass index, hypercoagulable conditions, autoimmune and inflammatory conditions, diabetes, open-angle glaucoma, hyperlipidemia, oral contraceptives, and optic disc edema, syphilis, sarcoidosis, sickle cell disease, and HIV disease.

Hypertension is the strongest risk factor for branch retinal vein occlusion.

Patients  need an assessment that may include fasting blood glucose level, hemoglobin A1c level, lipid profile, erythrocyte sedimentation rate, C-reactive protein level, syphilis testing, angiotensin-converting enzyme level, a complete blood cell count with differentials and platelets, and prothrombin time/partial thromboplastin time.

 

 

A hypercoagulable panel, ie, protein C activity, protein S activity, homocysteine, antiphospholipid antibody, antithrombin III, factor V Leiden,may need to be obtained. 

 

 

Patients should  be advised to cessation of smoking and maintaining a healthy weight and lifestyle.

Branch retinal main inclusion reportedly to be associated with other factors including diabetes, hyperlipidemia, smoking, and renal disease.

Following diabetic retinopathy, is the second most common retinal vascular disease to cause visual impairment.

Can occur as the central retinal vein exists the optic nerve head or at the common crossing point where the retinal artery compresses the branch of the vein.

Characterized by retinal hemorrhages and dilated veins thorough out the retina in the distribution of the central vein occlusion and in the distribution of the branch retinal vein occlusion.

Bilateral disease occurs in about 5% of cases.

In 10% of patients occlusion occurs in the other eye over time (Mckintosh RL et al).

Retinal vein wall damage from atherosclerosis contributes to stasis, thrombosis and eventually occlusion.

Hypercoagulability disorders, can also lead to formation of a thrombus, leading to damage of the involved retinal vessels and hemorrhaging.

Inflammatory processes may lead to retinal vein occlusion.

May be associated with hyperhomocysteinenemia, factor V Leiden mutation, protein C deficiency, protein S deficiency, prothrombin gene mutation and anti-cardiolipin antibodies.

Macula edema is the most frequent loss in eyes with retinal vein occlusions.

Leakage of edematous fluid from the impaired vasculature is another cause of vision loss, as it can cause separation of the retinal layers.

 

 

Edema occuring within the macula, decreases vision significantly.

Visual loss with retinal vein occlusion may also be due to neovascularization with vitreous hemorrhage, retinal detachment and neovascular glaucoma.

Branch retinal vein occlusion may be associated with a good prognosis with half of the patients returning to 20/40 vision or better within six months without treatment ( Finkelstein D).

In some cases tests such as visual acuity, visual field, afferent pupillary defect assessment, and electroretinography, or anatomical test such as retinal examination and fluorescein angiography can help you distinguish the clinical form of central retinal vein occlusion.

Early in retinal vein occlusion. changes in blood flow and circulation dynamics generate the release of inflammatory mediators such as interleukin-1, interleukin 2, interleukin-8, monocyte chemo attractant protein-1, VEGF and intracellular adhesion molecule-1, causing an increase in vascular permeability, leukocyte infiltration, and tissue remodeling.

As a result of above there is inflammation, endothelial malfunction and the development of edema.

In the Branch Vein Occlusion Study a randomized trial using laser treatment, only one third of untreated eyes with macula edema and vision of 20/40 or worse improved to better than 20-40 after three years, and one third developed retinal neovascularization of untreated eyes.

The prognosis is worse for patients with central retinal vein occlusion than in patients with branch retinal vein occlusion (McIintosh RL et al).

Neovascularization may develop in 20% of eyes and neovascular glaucoma and 60% of central vein occlusions (McIntosh RL et al).

Central retinal vein occlusion has different forms: nonischemic or venous stasis accounting for 65% of cases and has a 5% risk of associated neovascularization and neovascular glaucoma and ischemic or hemorrhagic central retinal vein occlusion accounts for 30% of cases, and has a 40-85% risk of neovascularization and neovascular glaucoma.

Central retinal vein occlusion of undetermined cause occurs in 5% of cases and conversion from nonischemic to ischemic central retinal vein occlusion occurs in 30% of cases.

Nonischemic CRVO often presents with unilateral sudden painless loss of vision. 

 

 

Examination of the posterior pole of the fundus reveals dot/blot hemorrhages in all 4 quadrants with mild dilation and tortuosity of the vessels. 

 

 

The resolution of nonischemic CRVO often begins within 6 to 12 months. 

 

 

In nonischemic CRVO vision usually returns to near-normal levels as long as it does not progress into an ischemic CRVO. 

 

Initially one third of eyes classified as having a perfused ocollusion may become non-perfused within the first year. 

Grid laser photocoagulation is the standard of care for macular edema associated with retinal vein occlusions.

Elevated levels of vascular endothelial growth factor in the vitreous and inflammation are implicated in its causation.

Major complications are macular edema and neovascular glaucoma.

Central retinal vein occlusion is associated with an overall increase in mortality compared with controls and is attributed statistically to cardiovascular disorders and diabetes.

There is no single therapy for the subtypes of retinal vein occlusion.

Treatment is prompt control of the inflammatory cascade and avoidance of potential complications of macular edema, which can permanent retinal damage and irreversible vision loss due to cystic degeneration, lamellar macula hole formation and epiretinal membrane formation and retinal atrophy.

Four options are available for treatment of macular edema: watchful waiting, pharmacologic therapies, laser photocoagulation, and surgery.

Two pharmacologic therapies are used and they are anti-VEGF and steroids.

Administer intravitreal corticosteroid or initiate an anti-vascular endothelial growth factor (anti-VEGF) treatment regimen are initiated.

 

 

Intravitreal corticosteroid can provide benefit in patients initially, but that benefit may regress. 

 

 

 BRVO is often managed with both laser photocoagulation and anti-VEGF injections if nonperfusion is present. 

 

 

Laser photocoagulation reduces the chance of neovascularization developing in patients with a BRVO.

Steroids have the advantage of targeting the three components of pathophysiology: to reduce macular edema in addition to multiple inflammatory mediators, they stabilize the blood retina barrier and they decrease vascular permeability and edema.

Three options for steroid treatment include triamcinolone, dexamethasone and fluocinolone.

Triamcinolone intravitreal injection can be used, but it is known to be associated with increased intraocular pressure and cataracts and repeated treating is needed to maintain efficacy.

Dexamethasone intravitreal implant 0.7 mg (Ozurdex) lasts for up to six months.

Results of the phase III GALILEO study of the efficacy of intravitreal aflibercept for macular edema secondary to central retinal vein occlusion indicate that the improvements in BCVA and retinal thickness achieved with 6 monthly injections can be maintained with careful monitoring and longer injection intervals.

177 patients with macular edema secondary to CRVO were randomized to receive 2 mg intravitreal aflibercept or sham every 4 weeks for 20 weeks.

The proportion of patients who gained ?15 letters in the intravitreal aflibercept and sham groups was 60.2% versus 22.1% at week 24.

The most common ocular serious adverse event in the intravitreal aflibercept group is macular edema (3.8%).

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