Blockage of Central Retinal Arteries and Veins
The central retinal artery, the main vessel that supplies blood to the retina, can become completely blocked because of atherosclerosis or particles, such as blood clots, that float in the bloodstream and block a vessel (emboli). Inflammation of the blood vessels is also a possible cause of retinal artery blockage. In people with glaucoma, diabetes, or high blood pressure, various processes may occur, which can lead to blockage of the veins.
If the central retinal artery is blocked, the affected eye has a sudden but painless loss of vision. Blockage of the central retinal vein causes engorged veins and swelling of the front of the optic nerve. Vision loss ranges from mild to severe as in central retinal artery blockage. Recurrences are common.
In addition to severe vision loss, complications of blockage of the central retinal artery or vein include hemorrhage into the eye and glaucoma caused by growth of abnormal blood vessels on the iris and angle, where fluid drains from the eye.
Diagnosis and Treatment
Using an ophthalmoscope, a doctor can see changes in blood vessels and other indications of decreased blood supply to the retina, such as paleness of the retina in the case of arterial blockage or engorged veins and swelling of the front of the optic nerve in the case of venous blockage. Fluorescein angiography--a procedure in which a doctor injects dye into a vein and then photographs the retina--helps determine the extent of damage to the retina and helps the doctor plan treatment. Doppler ultrasound scanning may sometimes be used to observe blood flow in the vessels.
Immediate treatment is often given in an attempt to unblock the retinal artery. However, treatments are rarely effective. Pressure inside the eye can be lowered by intermittently massaging the closed eyelids with the fingers. Alternatively, a procedure called anterior chamber paracentesis may help lower pressure inside the eye. In this procedure, drops are placed in the eye to numb the eye, and then a needle is inserted into the anterior chamber of the eye to withdraw a small amount of fluid, thereby rapidly lowering the pressure in the eye. Lowering the pressure inside the eye by massage or by anterior chamber paracentesis may dislodge a blood clot or other embolus and allow it to enter a smaller branch of the vessel, thereby reducing the area of damage to the retina. There is no generally accepted drug therapy. Laser treatment may be used to destroy abnormal blood vessels if they develop on the iris or angle.
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