High blood pressure, medically known as hypertension, affects all the blood vessels in the body, including those found in the eye. Blood vessel changes often lead to hemorrhage, or blood leakage, inside the eye, which is not visible from the outside of the eye. Changes to the blood vessels in the eye may cause no noticeable symptoms at all, or they may significantly interfere with vision, depending on where the hemorrhages are located.
Branch Retinal Vein Occlusion (BRVO)
A blockage of the veins in the retina causes blood to back up behind the blockage and hemorrhage into the retina. Branch Retinal Vein Occlusion (BRVO), often caused by hypertension, is the most common type of blockage in the retina, according to the Angeles Vision Clinic, occurring equally in males and females, and usually affecting those in their 60s and 70s. Blockage often occurs where a vein and artery cross; hardening of the artery that lies across the vein compresses the vein and slows blood flow through it, the New York Eye and Ear Infirmary explains.
If large parts of the retina receive no blood supply due to the blockage, new blood vessels form to compensate. These abnormal new blood vessels cause hemorrhage into the vitreous, the gel found in the middle of the eyeball, in 60 percent of cases unless laser therapy is initiated to destroy the abnormal vessels. The macula, the central part of retinal vision, often hemorrhages in the first three to six months after a BRVO develops. Vision loss and sometimes floaters, small dots or strings that pass across the line of vision, may be signs of BRVO, although vision loss may not be significant if the blockage is out of the central line of vision.
Central Retinal Vein Occlusion (CRVO)
Central retinal vein occlusion (CRVO) is blockage in the vein near the optic nerve, which collects all the blood from the retina to carry it back to the heart. Hypertension is a primary cause of CRVO. A small clot, or thrombus, blocks the blood vessel; blood backs up behind the clot and leaks out of the blood vessels. Painless vision loss usually accompanies CRVO, the Merck Manual reports. Small hemorrhages can be seen throughout the retina if photos of the back of the eye are taken. An ophthalmologist can see these during a dilated eye exam. Neovascularization occurs less frequently than in cases of BRVO, and laser may not be effective for CRVO as for BRVO, according to the Angeles Vision Clinic.
Vitreous Hemorrhages
Vitreous hemorrhages occur when blood from abnormal blood vessels in the retina leak into the gel in the center of the eye, called the vitreous. Blocked retinal veins from hypertension often cause these new blood vessels to grow. Hemorrhage into the vitreous blocks light from reaching the retina and causes painless vision loss, which can be severe. Floaters and flashes of light also may be seen. Small vitreous hemorrhages may resolve on their own. Severe vitreous hemorrhage can be treated by surgical removal of the vitreous. Saline is instilled into the vitreal space to maintain the shape of the eye.
