Retinal vein occlusion

Arteriolosclerosis is an important factor contributing to the development of branch retinal vein occlusion. Retinal arterioles and their corresponding veins share a common adventitial coat, so thickening of the arterioles causes compression of the vein if the arteriole is anterior to the vein. This leads to secondary changes, including loss of venous endothelial cells, thrombus formation, and occlusion. Similarly, the central retinal vein and artery share a common adventitial coat behind the lamina cribrosa, so atherosclerotic changes in the artery can cause compression of the vein and provoke occlusion of the central retinal vein. In this regard, it is believed that damage to both arteries and veins leads to venous occlusions of the retina. In turn, venous occlusion leads to an increase in pressure in the veins and capillaries with a slowdown in blood flow. This contributes to the development of retinal hypoxia, from which blood is diverted through the obstructed vein. Subsequently, damage to the capillary endothelial cells and extravasation of blood components occurs, the pressure on the tissue increases, causing even greater slowing of circulation and hypoxia. Thus, a vicious circle is established.

Classification of retinal vein occlusion

1. Branch retinal vein occlusion.
2. Central retinal vein occlusion.
   • Non-ischemic.
   • Ischemic.
   • Papillophlebitis.
3. Hemiretinal venous occlusion.

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What causes retinal vein occlusion?

The following are conditions listed in order of severity that are associated with a high risk of developing retinal venous occlusion.

1. Old age is the most important factor; more than 50% of cases affect patients over 65 years of age.
2. Systemic diseases including hypertension, hyperlipidemia, diabetes, smoking and obesity.
3. Elevated intraocular pressure (eg, primary open-angle glaucoma, ocular hypertension) increases the risk of developing central retinal vein occlusion.
4. Inflammatory diseases such as sarcoidosis and Behcet's disease may be accompanied by retinal occlusive periphlebitis.
5. Increased blood viscosity associated with polycythemia or abnormal plasma proteins (eg, myeloma, Waldenstrom's myeloma).
6. Acquired thrombophilias, including hyperhomocysteinemia and antiphospholipid syndrome. Elevated plasma homocysteine levels are a risk factor for myocardial infarction, strokes, and carotid artery disease, as well as central retinal vein occlusion, especially of the ischemic type. Hyperhomocysteinemia is in most cases rapidly reversible with the conversion of folic acid.
7. Congenital thrombophilias may be accompanied by venous occlusion in young patients. This is accompanied by increased levels of coagulation factors VII and XI, deficiency of anticoagulants such as antithrombin III, protein C and S, and resistance to activated protein C (factor V Leiden).

Factors that reduce the risk of developing venous occlusion include increased physical activity and moderate alcohol consumption.

Branch retinal vein occlusion

Classification

1. Occlusion of the main branches of the central retinal vein is divided into the following types:
   • Occlusion of the first order temporal branch near the optic disc.
   • Occlusion of the first-order temporal branch away from the optic disc but including the branches that feed the macula.
2. Occlusion of small paramacular branches, covering only the branches that feed the macula.
3. Occlusion of peripheral branches that do not include the macular circulation.

Clinical features

The manifestations of branch retinal vein occlusion depend on the volume of the macular outflow system that is occluded. When the macula is involved, there is a sudden deterioration in vision, metamorphopsia, or relative scotomas of the visual fields. Peripheral branch occlusion may be asymptomatic.

Visual acuity varies and depends on the extent of the pathological process in the macular region.

Fundus of the eye

• Dilation and tortuosity of the veins peripheral to the site of occlusion.
• Flame-like hemorrhages and pinpoint hemorrhages, retinal edema and cotton-wool spots located in the sector corresponding to the affected branch.

Foveal angiography in the early phases reveals hypofluorescence due to blocking of background choroidal fluorescence by retinal hemorrhages. In the late phases, hyperfluorescence due to sweating is detected.

Course. Manifestations in the acute period can last 6-12 months until complete resolution and are expressed as follows:

• The veins are sclerotic and surrounded by varying amounts of residual hemorrhage peripheral to the area of obstruction.
• Venous collaterals, characterized by moderate tortuosity of the vessels, develop locally along the horizontal suture between the inferior and superior vascular arcades or near the optic nerve head.
• Microaneurysms and hard exudates may be combined with the deposition of cholesterol inclusions.
• In the macular region, changes in the retinal pigment epithelium or epiretinal gliosis are sometimes detected.

Forecast

The prognosis is quite favorable. Within 6 months, approximately 50% of patients develop collaterals with vision restoration to 6/12 and above. Improvement of visual functions depends on the extent of venous outflow damage (which is associated with the location and size of the blocked vein) and the severity of macular ischemia. There are two main vision-threatening conditions.

Chronic macular edema is the main cause of long-term vision loss after branch retinal vein occlusion. Some patients with visual acuity of 6/12 or worse may benefit from laser photocoagulation, which is more effective for edema than ischemia.

Neovascularization. Neovascularization develops in the disc area in approximately 10% of cases, and away from the disc in 20-30%. Its probability increases with the severity of the process and the extent of the lesion. Neovascularization outside the optic nerve disc usually develops at the border with the triangular sector of the ischemic retina, where there is no outflow due to vein occlusion. Neovascularization can develop at any time during the 3 years, but most often it appears in the first 6-12 months. This is a serious complication that can cause recurrent vitreous hemorrhages and preretinal hemorrhages, and sometimes traction retinal detachment.

Observation

Patients need to undergo foveal angiography in the interval of 6-12 weeks, during which sufficient resorption of retinal hemorrhages occurs. Further tactics depend on visual acuity and angiographic findings.

• FAG reveals good macular perfusion, visual acuity improves - no treatment required.
• Foveal angiography reveals macular edema in combination with good perfusion, visual acuity remains at 6/12 and below, after 3 months a decision is made about laser coagulation. But before treatment, a detailed examination of the FAG is important to determine the sweating zones. No less important is the detection of collaterals that do not allow fluorescein to pass through and should not be coagulated.
• FAG reveals the absence of macular perfusion, visual acuity is low - laser coagulation for improving vision is ineffective. However, if Foveal angiography shows no perfusion of the area up to 5 or more DD, then it is necessary to examine the patient every 4 months for 12-24 months due to possible neovascularization.

Laser treatment

1. Macular edema. Lattice laser coagulation is performed (the size of each coagulate and the distance between them is 50-100 μm), which causes a moderate reaction in the area of sweating revealed by foveal angiography. Coagulates should not be applied beyond the avascular zone of the fovea and peripheral to the main vascular arcades. It is necessary to be careful and avoid coagulation of areas with intraretinal hemorrhages. Follow-up examination - in 2-3 months. If macular edema persists, repeated laser coagulation may be performed, although the result is often disappointing.
2. Neovascularization. Scattered laser coagulation is performed (the size of each coagulate and the distance between them is 200-500 μm) to achieve a moderate reaction with full coverage of the pathological sector, previously identified on color photography and fluorography. Repeated examination - after 4-6 weeks. If neovascularization persists, repeated treatment usually gives a positive effect.

Non-ischemic central retinal vein occlusion

Clinical features

Non-ischemic central retinal vein occlusion presents with sudden unilateral loss of visual acuity. Visual impairment is moderate to severe. Afferent pupillary defect is absent or weak (unlike ischemic occlusion).

Fundus of the eye

• Varying degrees of tortuosity and dilation of all branches of the central retinal vein.
• Pinpoint or flame-like retinal hemorrhages in all four quadrants, most abundant in the periphery.
• Sometimes cotton-wool-like lesions are found.
• Mild to moderate swelling of the optic disc and macula is often noted.

Arteriography reveals delayed venous outflow, good retinal capillary perfusion, and delayed oozing.

Non-ischemic central retinal vein occlusion is the most common and accounts for about 75% of cases.

Course. Most acute manifestations disappear after 6-12 months. Residual effects include optic disc collaterals, epiretinal gliosis, and pigment redistribution in the macula. Transition to ischemic occlusion of the central retinal vein is possible within 4 months in 10% of cases, and within 3 years in 34% of cases.

Forecast

In cases where the process does not become ischemic, the prognosis is quite favorable with complete or partial restoration of vision in approximately 50% of patients. The main cause of poor restoration of vision is chronic cystic macular edema, which leads to secondary changes in the retinal pigment epithelium. To a certain extent, the prognosis depends on the initial visual acuity, namely:

• If at the beginning the visual acuity was 6/18 or higher, then most likely it will not change.
• If visual acuity was within the range of 6/24-6/60, the clinical course varies, and vision may subsequently improve, remain unchanged, or even worsen.
• If visual acuity was 6/60 at baseline, improvement is unlikely.

Tactics

1. Observation is necessary for 3 years to prevent transition to the ischemic form.
2. High-power laser treatment is aimed at creating anastomoses between the retinal and choroidal veins, thereby creating parallel branches in the area of venous outflow obstruction. In some cases, this method gives good results, but is associated with a potential risk of complications such as fibrous proliferation in the area of laser exposure, venous or choroidal hemorrhage. Chronic macular edema will not respond to laser treatment.

Ischemic central retinal vein occlusion

Clinical features

Ischemic retinal vein occlusion is characterized by unilateral, sudden and severe visual impairment. Visual impairment is almost irreversible. Afferent pupillary defect is severe.

Fundus of the eye

• Marked tortuosity and congestion of all branches of the central retinal vein.
• Extensive spotted and flame-like hemorrhages involving the periphery and posterior pole.
• Cotton-like lesions, of which there may be many.
• Macular edema and hemorrhages.
• Severe swelling of the optic disc and hyperemia.

Foveal angiography reveals central retinal hemorrhages and extensive areas of capillary nonperfusion.

Course. The manifestations of the acute period disappear within 9-12 months. Residual changes include optic disc collaterals, epiretinal macular gliosis and pigment redistribution. Less commonly, subretinal fibrosis may develop, similar to that in the exudative form of age-related macular degeneration.

The prognosis is extremely unfavorable due to macular ischemia. Rubeosis iridis develops in approximately 50% of cases, usually within 2 to 4 months (100-day glaucoma). If panretinal laser coagulation is not performed, there is a high risk of developing neovascular glaucoma.

Tactics

Monitoring is performed monthly for six months to prevent anterior segment neovascularization. Although anterior segment neovascularization does not necessarily indicate the presence of neovascular glaucoma, it is the best clinical marker.

Therefore, if there is a risk of developing neovascular glaucoma, detailed gonioscopy is necessary, since examination using only a slit lamp is considered inadequate.

Treatment. If neovascularization of the anterior chamber angle or iris is detected, panretinal laser coagulation is performed immediately. Preventive laser coagulation is suitable for cases where regular monitoring is not possible. However, sometimes retinal hemorrhages have not resolved sufficiently by the time laser coagulation is performed.

Papillophlebitis

Papillophlebitis (vasculitis of the optic nerve head) is considered a rare condition, usually occurring in healthy individuals under 50 years of age. It is believed that the disorder is based on optic nerve head edema with secondary venous occlusion, as opposed to venous thrombosis at the level of the cribriform plate in the elderly.

It is manifested by a relative deterioration of vision, most often noted when rising from a lying position. Deterioration of vision is from minor to moderate. There is no afferent pupillary defect.

Fundus:

• Papilledema, often in combination with cotton wool spots, is dominant.
• Dilation and tortuosity of veins, hemorrhages expressed to varying degrees and usually limited to the parapapillary zone and the posterior pole.
• The blind spot is enlarged.

Foveal angiography reveals delayed venous filling, hyperfluorescence due to oozing, and good capillary perfusion.

The prognosis is excellent regardless of treatment. In 80% of cases, vision is restored to 6/12 or better. The rest experience significant irreversible vision loss due to macular edema.

Hemiretinal venous occlusion

Hemiretinal vein occlusion is less common than central retinal vein occlusion and involves the superior or inferior branches of the central retinal vein.

Classification of hemiretinal vein occlusion

• occlusion of the hemisphere of the main branches of the central retinal vein near the optic disc or at a distance;
• Hemicentral occlusion is less common, involves one of the two trunks of the central retinal vein, and is found on the anterior surface of the optic disc as a congenital occlusion.

Hemiretinal venous occlusion is characterized by sudden loss of vision in the upper or lower half of the visual field, depending on the affected area. Visual impairment varies.

Fundus: The picture is similar to occlusion of the branch of the central retinal vein with involvement of the superior and inferior hemispheres.

Foveal angiography reveals multiple hemorrhages, hyperfluorescence due to sweating, and various disturbances of retinal capillary perfusion.

The prognosis is determined by the degree of macular ischemia and edema.

Treatment depends on the severity of retinal ischemia. Significant retinal ischemia is associated with the risk of developing neovascular glaucoma, so management is the same as for ischemic central retinal vein occlusion.