What You Should Know About Branch and Central Retinal Vein Occlusions

What is a retinal vein occlusion?
The retina is nourished by tiny blood vessels that bring blood into (arteries) and out of (veins) the eye. Occasionally an artery will compress the underlying vein, making it difficult for blood to exit the eye. This blockage, called a branch retinal vein occlusion, causes the vein to dilate and leak fluid and blood. The main vein exiting the eye can also become blocked within the optic nerve, causing a central retinal vein occlusion. Retinal vein occlusions are more common in older individuals as well as persons with hypertension, diabetes, or glaucoma.
 

Branch retinal vein occlusion.		Central retinal vein occlusion.

Macular edema develops when the occlusion involves the macula, causing it to swell with fluid and blood. Central vision can become blurred, just as a water droplet placed on a photograph will cause the picture to blister and become distorted. Macular edema develops in 60% of branch retinal vein occlusions and virtually all central retinal vein occlusions.

Retinal vein occlusions can also decrease the overall retinal blood supply.  Some eyes will develop tiny new blood vessels along the retinal surface in an attempt to increase the retinal blood supply (retinal neovascularization).  These new vessels do not help the eye, however. They are fragile and can cause blindness by hemorrhaging or retinal detachment. Retinal neovascularization develops in about 25% of eyes with branch retinal vein occlusions and rarely in eyes with central retinal vein occlusion.

Eyes with central retinal vein occlusion are classified into the non-ischemic (good retinal arterial circulation) and ischemic (poor circulation) types. Up to two-thirds of eyes with ischemic central retinal vein occlusion (compared with virtually none of the non-ischemic occlusions) develop new blood vessels on the surface of the pupil (iris neovascularization). Iris neovascularization usually develops within the first six months of the occlusion. These vessels can block the outflow of fluid from the eye, causing pain with very high pressures inside the eye (neovascular glaucoma).

Fluorescein angiogram of a non-ischemic central retinal vein occlusion.  The white dye fills the capillaries between the larger retinal vessels		Fluorescein angiogram of an ischemic central retinal vein occlusion shows near total capillary loss, along with leakage from retinal neovascularization.

What are the symptoms of a retinal vein occlusion?
Retinal vein occlusions can cause blurring of the central and peripheral vision. Central retinal vein occlusions generally cause more severe loss when compared to branch retinal vein occlusions. Patients may be completely asymptomatic, especially when the other eye sees normally.  Neovascular glaucoma can cause severe eye redness, pain, nausea, and total blindness.

How is a retinal vein occlusion diagnosed?
You can't diagnose a retinal vein occlusion by looking in the mirror since your eye will usually look and feel normal. The diagnosis is made with a thorough retinal examination through a dilated pupil. Additional testing, including fluorescein angiography, may be performed to better diagnose and assess the need for treatment. Fluorescein angiography is a photographic test, not involving x-rays, in which a colored vegetable dye is injected into an arm vein. A series of photographs are taken as the dye passes through the back of the eye.

What treatments are available for retinal vein occlusions?

1. Macular edema.

a) Branch retinal vein occlusion.

• Laser Photocoagulation.
  Patients are usually examined every several months before considering treatment since many eyes will spontaneously improve. Macular grid laser photocoagulation should be considered if macular edema explains the visual loss and vision continues to be 20/40 or worse.  Additional treatments should be considered if visual loss from macular edema persists at the 4-month follow-up examinations. The Branch Vein Occlusion Study found that photocoagulation improved the visual prognosis at the 3-year follow-up visit. The average vision was 20/40 to 20/50 in the treated eyes compared to 20/70 in the untreated eyes. The treated eyes gained an average of 1.33 lines of vision compared to 0.23 lines in the untreated eyes. A gain of at least 2 lines of vision occurred in 65% of the treated eyes compared to 37% of the untreated eyes. Vision was at least 20/40 in 60% of the treated eyes compared to 34% of the untreated eyes. Vision was 20/200 or worse in 12% of the treated eyes compared to 23% of the untreated eyes.
  
• Intraocular steroids. Although laser photocoagulation was the only treatment available for branch retinal vein occlusion-related macular edema since the 1970's, the recent advent of intraocular steroids has added another successful treatment for this disease. Injection of anti-inflammatory steroid medication (Kenalog) into the eye (a painless in-office procedure) appears to rapidly improve macular edema and vision loss, often more successfully than laser. However, the injections often have to be repeated every 4-6 months, and the long-term visual results remain to be determined. Temporarily increased eye pressure (glaucoma) and cataract are the most common and treatable side-effects. Pending ongoing studies, the role of laser photocoagulation versus intraocular steroids is still unclear. Your doctor will discuss which treatment, if any, he feels would be best for your eye.

b) Central retinal vein occlusion.

• Laser photocoagulation. The Central Vein Occlusion Study found that macular grid photocoagulation was effective in decreasing angiographic macular edema. However, such treatment was not recommended since laser had no effect on the visual prognosis.
  

Macular edema and hemorrhages before laser surgery.		Resolution of macular edema 4 months following laser.

• Intraocular steroids. Injection of anti-inflammatory steroid medication (Kenalog) into the eye (a painless in-office procedure) appears to improve macular edema and vision loss. However, the injections often have to be repeated every 4-6 months, and the long-term visual results remain to be determined. Temporarily increased eye pressure (glaucoma) and cataract are the most common and treatable side-effects.
  
  
• Radial optic neurotomy. Radial optic neurotomy is a newly described hospital surgery that offers new hope for patients suffering severe vision loss from central retinal vein occlusion. The optic nerve exits the eye in a relatively small opening in the back of the eye; this tight ring of tissue surrounding the nerve may literally help to squeeze the vein closed. Radial optic neurotomy directly releases this "napkin-ring" compression with a microscopic incision in the margin of the nerve, making it easier for blood to exit the eye. Preliminary data shows that patients often show dramatic improvement in the retinal hemorrhages, macular edema, and vision within several months of surgery.

2) Retinal neovascularization.  

a) Branch retinal vein occlusion.
Patients should be examined every 4 months to look for the possible development of disc or peripheral retinal neovascularization. Panretinal laser photocoagulation (similar to that performed for proliferative diabetic retinopathy) is performed if neovascularization develops. Laser photocoagulation decreases the chance of developing vitreous hemorrhage (29% with laser vs. 61% without treatment). Additional treatment should be considered if neovascularization persists at the 4-month follow-up examinations.

Some eyes will develop severe vision loss if retinal neovascularization bleeds into the vitreous. Vitrectomy with removal of the vitreous hemorrhage is often successful in restoring vision. Vitrectomy surgery is done at the hospital under local anesthesia.

b) Central retinal vein occlusion. 
Retinal neovascularization is rare in eyes with central retinal vein occlusions. Panretinal photocoagulation, as performed for eyes with proliferative diabetic retinopathy, is effective in preventing further bleeding and vitreous hemorrhage from these new vessels.

3) Neovascular glaucoma.
Neovascular glaucoma develops solely in eyes with central retinal vein occlusions. Patients with central retinal vein occlusion should be examined monthly during the first 6 months of the occlusion, the period when eyes are at the highest risk for developing iris neovascularization. Close follow-up is particularly important for high-risk eyes (less than one month of symptoms and with those with visual acuity worse than 20/200).

Prophylactic treatment is not generally recommended, although it should be considered for patients with high-risk characteristics if close follow-up is not possible or seems unlikely. Prompt panretinal photocoagulation (as performed for eyes with proliferative diabetic retinopathy) should be applied once iris neovascularization develops. Patients require monthly examinations following laser to determine whether additional treatment is required for persistent iris neovascularization. The frequency of subsequent examinations can be safely tapered once anterior segment neovascularization regresses. The Central Vein Occlusion Study found that this protocol was highly effective in preventing the development of neovascular glaucoma.