Central Retinal Vein Occlusion - Causes, Symptoms, Diagnosis, and Treatment

Introduction

Central retinal vein occlusion (CRVO) is defined as the obstruction of the main central vein of the retina posterior to the optic nerve. The block is caused by the formation of blood clots (thrombi) inside the blood vessels. CRVO is among the diseases affecting the retina's blood vessels.

What Is the Normal Anatomy and Blood Supply of Retina?

The retina is present at the back of the eye. It sends the acquired images to the brain, requiring a rich blood supply and drainage. The retinal vein occlusion is of three types: central, hemi, and branch. Central retinal vein occlusion (CRVO) occurs when the central retinal vein thromboses while passing through the lamina cribrosa (a section of the posterior sclera that functions as a sieve and lets optic nerve fibers leave the eye). Venous thrombosis at an arteriovenous crossing, where an artery and vein share the same vascular sheath, is the cause of branch retinal vein occlusion (BRVO). The upper or lower half of the retina can be affected by hemi-retinal vein occlusions, which are variations of central retinal vein occlusions.

What Are the Causes of CRVO?

CRVO primarily occurs due to the formation of thrombi. However, the exact cause of the disease sometimes remains elusive.

The critical principles responsible for the retinal vein block are:

• Stasis of the blood flow.

• Increased coagulability of the blood.

• Formation of thrombi.

What Are the Risk Factors Linked to CRVO?

CRVO is a retinal disease of old age that is significantly above fifty years of age. Other factors responsible for CRVO are:

• Hypertension.

• Diabetes

• Consumption of oral contraceptive pills.

• Smoking.

• Increase in intraocular pressure.

• Increase in serum plasma protein concentration.

• Hypercoagulable states like hyperhomocysteinemia.

• Protein C and S deficiency.

• Behcet's syndrome.

• Sarcoidosis.

• Renal failure.

• Orbital diseases.

• Severe dehydration in tropical countries.

How Prevalent Is Retinal Vein Occlusion?

The most frequent condition damaging the retina is diabetes-related retinopathy, with retinal vein blockage coming in second. Researchers calculate that, on a worldwide scale:

• More than 16 million people suffer from retinal vein occlusion.

• One to four persons out of every 1,000 are affected by central retinal vein occlusion.

• Approximately 6 to 12 persons per 1,000 are affected by branch retinal vein occlusion.

How Is the Blood Clot Formed in CRVO?

The build-up of fats inside the retinal artery (atherosclerosis) leads to compression of the adjacent retinal vein. The narrowing of the vein leads to stasis of the blood flow, ultimately contributing to the formation of thrombi.

What Are the Different Forms of CRVO?

Based on the perfusion of the region, it is divided into:

• Ischemic CRVO is a severe form of CRVO with a poor prognosis concerning visual acuity.

• Nonischemic CRVO is a more common and milder form of the disease state. It is also known as impending and partial.

What Are the Clinical Signs and Symptoms of CRVO?

Patients with CRVO complain of sudden blurred vision and reduced color vision.

• The blurring of vision is mild, with visual acuity of more than 20/200.

• The blurring of vision occurs mainly after waking up in the case of non-ischemic form.

• Ischemic CRVO is severe with a pronounced afferent pupillary defect (different response of the pupil to light stimuli at a time). As a result, visual acuity is less than 20/200, and extensive retinal bleeding, optical disc edema, and excessive blood in different eye parts (hyperemia) are present.

• Ischemic CRVO is more prone to blindness.

How Are CRVO Patients Diagnosed?

Diagnosis of CRVO is achieved by a complete physical evaluation of the eye, imaging, and extensive laboratory workup.

• Eye imaging, like fluorescence angiography and optical coherence tomography (OCT) are used.

• Fluorescence angiography (FA) reveals delayed staining of the large blood vessels in the case of non-ischemic CRVO. Ischemic CRVO shows areas with less blood supply leading to reduced oxygenation and the formation of new blood vessels inside the retina.

• Time FA helps determine the severity of the capillary permeability and degree of retinal blood vessel obstruction.

• OCT is solely effective in monitoring the severity and course of swelling of the macula (macular edema) before and after treatment.

• Fundus autofluorescence helps investigate recent infections based on the fluorescence property of the vessels that are masked in the case of ischemic CRVO.

• The region around the retinal vein (perivenular), specifically in the posterior pole, frequently exhibits ischemic edema.

• Laboratory tests are performed in the case of CRVO with underlying diseases. Some tests are performed in all patients, while some are performed in patients with basal pathologies.

The tests include:

• Blood sugar.

• Blood pressure.

• Complete blood count (CBC).

• Blood cholesterol.

• Plasma protein concentration.

• Electrolyte tests.

• Thyroid function tests.

• Electrocardiogram (ECG).

• Specific tests performed in patients below the age of fifty with bilateral involvement of CRVO and previous thrombosis history include:

• Chest X-ray.

• C-reactive proteins.

• Thrombophilia screen.

• Serum angiotensin-converting enzyme concentration.

• Carotid duplex imaging.

What Are the Diseases That Mimic CRVO?

Diseases with similarities to CRVO are:

• Ocular ischemic syndrome.

• Proliferative diabetic retinopathy.

• Branch retinal vein occlusion.

How Are Patients With CRVO Managed?

There is no specific treatment for preventing and managing CRVO. However, CRVO often leads to the release of vascular endothelial growth factors (VEGF) and forms new blood vessels. Intravitreal injections of anti-VEGF factors intercept this. Other drugs administered for CRVO are:

• Aspirin.

• Systemic anticoagulants.

• Fibrinolytic agents break the fibrin clots.

• Intravitreal injection of corticosteroids.

• Surgical Interventions Comprise:

1. Laser photocoagulation.

2. Chorioretinal venous anastomosis.

3. Radial optic neurotomy.

4. Pars plana vitrectomy.

Regular follow-up of patients, even after the treatment, is crucial to avoid further complications.

What Are the Different Approaches Taken to Prevent CRVO?

Patients are educated about the importance of consultation with the ophthalmologist in case of sudden vision loss. The first step in preventing retinal vein occlusion is being aware of the risk. It is crucial to discuss any underlying medical disorders that could increase the likelihood of blood flow issues with the primary care physician. As necessary, they will suggest therapies to control such diseases and support the general health of the body, including the eyes. A few preventive measures appropriate for any other vascular disease that aid in the prevention of CRVO are:

• Regular exercise.

• Weight control.

• Low-fat diet.

• Avoidance of smoking.

What Are the Complications of CRVO?

Complications are more familiar with ischemic CRVO. The retina's reduced oxygenation due to the blocking of the vein results in the release of VEGF and other inflammatory mediators. These factors contribute to the development of further complications.

The common complications of CRVO are:

• Macular edema.

• Vitreous hemorrhage.

• Neovascular glaucoma.

• Iris neovascularization.

What Is the Prognosis of CRVO?

Numerous variables, including the obstruction's location and associated consequences, affect the prognosis. While some people's vision gradually improves over time, others suffer lifelong damage to their eyesight. Their physician can refer individuals to vision rehabilitation, which teaches them how to live with less vision. This could involve using tools like assistive computer technology or magnifying glasses.

The prognosis of non-ischemic CRVO is reasonable in comparison to ischemic CRVO and shows spontaneous improvement in a few patients. The prognosis is also favorable for younger patients. Macular edema, a complication of ischemic CRVO, is chiefly responsible for vision loss.

Conclusion

CRVO is the second most common vascular disease. It is mainly caused by the mechanical compression of the retinal veins. Patients suffer from a sudden blurring of vision. The ischemic form of the disease shows a poorer prognosis. Appropriate treatment with regular follow-up for up to two years aids in achieving a favorable outcome.