Vein occlusion

Retinal veins drain blood from the retinal arteries and capillaries and send it back to the heart.  Retinal vein occlusion occurs when a retinal vein becomes blocked.  The blockage leads to the poor blood flow and damage to the blood vessel walls, causing the blood and the fluid to leak into the retina and damage the photoreceptors essential for normal vision.

Types
There are two types of retinal vein occlusion

    • Central retinal vein occlusion:  There is one central retinal vein in each eye.  It is the main vein that all the smaller branch retinal veins merge into.  The occlusion of the central retinal vein often leads to severe visual loss due to the extensive areas involved.

    • Branch retinal vein occlusion:  A branch vein is occluded, resulting in a localized damage to the retina.  Severity of visual loss depends on the location of the occluded branch.  If the branch occluded is near the center of the vision, visual loss can be significant.

Causes
The most common cause of the vein occlusion is arteriosclerosis, a hardening of the crossing artery due to plaques build-up, resulting in the narrowing of the vein and eventual blockage.  This process is similar to the pathologic process underling the stroke and heart attack.  Retinal vein occlusion is more common in certain people who have hypertension, glaucoma, diabetes, older age, and blood disorders.

Symptoms
Sudden onset of blurred vision in one eye is the most common presenting symptoms.  This occurs when the central part of the retina, called macula, develops swelling due to the leakage of fluid from the occluded vein.  Pain is usually absent unless high eye pressure develops inside the eye due to the growth of abnormal blood vessels in the iris in response to the chronic poor oxygenation.  This condition, called neovascular glaucoma, portends poor prognosis and usually require laser surgery.  Sometimes bleeding into the vitreous cavity of the eye can occur if the abnormal blood vessels grow on the surface of the retina.  This can cause sudden appearance of moving black spots in vision.

Diagnostic tests
Complete eye examination with dilation of the pupil is needed to diagnose retinal vein occlusion.  Special tests such as fluorescein angiogram and OCT help diagnose and plan treatment strategy.

Treatment
Laser surgery is often used to reduce swelling or prevent growth of abnormal blood vessels.  Intraocular injection of anti-angiogenic drugs such as steroids and avastin represents new treatment when laser treatment is not feasible. Pars plana vitrectomy is sometimes used in case of severe bleeding into the vitreous cavity of the eye.  Evaluation by primary care physician is often encouraged to treat any contributing systemic diseases such as hypertension and hyperlipidemia.

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