GLAUCOMA
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Neovascular Glaucoma

What is Neovascular Glaucoma?
Neovascular glaucoma is an unusual type of closed-angle glaucoma which can be particularly difficult to treat. In many instances, it is first recognized when a patient notes a sudden loss of vision, a red and uncomfortable eye, or even pain.



What Causes Neovascular Glaucoma?
This condition is considered to be a type of closed-angle glaucoma because the trabecular meshwork, the tiny drain through which aqueous humor (the clear fluid which nourishes the front of the eye) exits the eye, is closed or blocked. This results directly from the growth of new blood vessels (neovascularization), which are not normally present in this location. This is why the condition is known as neovascular glaucoma.

As the blood vessels grow, they are first accompanied by an almost invisible fibrous tissue which is like a thin scar. This tissue blocks the drainage of the fluid through the trabecular meshwork. The fluid accumulates within the eye and causes the eye pressure to increase. If this happens over a short period of time, the patient may have sudden pain. If the blockage of the drain occurs more slowly, there may only be redness with some discomfort. In both situations, the eye pressure needs to be lowered if vision is to be saved.

Who is at Risk for Developing Neovascular Glaucoma?
Neovascular glaucoma occurs in individuals in whom there is poor blood flow to the eye. Blood provides much of the eye with nourishment, including oxygen, and removes wastes from it. In addition, the clear aqueous humor, which nourishes some of the inner portions of the eye, can only be properly formed if there is an adequate blood supply.

Who is at Particular Risk?
Blood flow in individuals with diabetes often is reduced in many parts of the body, including the eyes, particularly when the diabetes has been present for more than ten years. In other individuals, there may be a sudden blockage of an important blood vessel within the eye by a blood clot or other change. This tends to happen most often when there is high blood pressure in the body. High eye pressure, as occurs in individuals with untreated open-angle glaucoma, can predispose to this by tending to collapse the blood vessel from the outside. Finally, there may be impaired blood flow to the eye when the large blood vessels which supply the entire head (and smaller blood vessels to the eye) are narrowed with aging.

Why do New Blood Vessels Grow in Neovascular Glaucoma?
When the blood vessels to the eye are partially or completely blocked, the surrounding structures in the eye are starved for nourishment and oxygen. In response to this, they make certain chemicals which lead to the formation of new blood vessels, a process known as neovascularization. Most often this occurs first in the back of the eye on the retina. However, these chemicals can seep to the front of the eye over a period of three months, and cause neovascularization to grow over the iris (the colored portion of the eye) and the trabecular meshwork. As these new blood vessels grow, the iris is pulled against and becomes adherent to the trabecular meshwork, permanently blocking the drainage path.

How is Neovascular Glaucoma Treated?
Treatment is directed toward two goals. First, eye pressure needs to be lowered immediately to prevent it from further damaging the optic nerve. Initially, this is done through use of medications that reduce the amount of aqueous humor which flows into the eye. Eye drops, particularly beta-blocking agents, and a pill, such as acetazolamide, are most effective in this regard.

Second, it is necessary to treat the eye and eliminate the neovascularization. This is particularly important if the glaucoma is recognized early so that the drain is not completely blocked. In this case, eliminating the neovascularization may preserve a portion of the trabecular meshwork which can continue to drain aqueous humor to maintain a safe eye pressure.The neovascularization is most effectively eliminated by destroying the structures which are poorly nourished as a result of the reduced blood flow. These structures are usually in the back of the eye in the retina. Destroying these structures eliminates the chemicals which stimulate the formation of new blood vessels in the front of the eye.

How is This Accomplished?
The most effective way to treat the eye is using a laser beam which is focused through the eye to burn the retina. This is known as retinal photocoagulation. It is necessary for the ophthalmologist to have a clear view of the retina in order to do this. If the view is not clear, the ophthalmologist may freeze the retina from the outside in order to destroy it, an operation known as retinal cryotherapy.

If the neovascularization persists, and even if it is no longer present, it may not be possible to lower the eye pressure sufficiently with eye drops and pills. In this case, it is necessary to reduce the eye pressure through surgery. Trabeculectomy or placement of a minute tube (known as a seton) are most widely used to drain aqueous in eyes which still have the potential for sight. In eyes with only limited potential for sight, your eye doctor might recommend a type of surgery in which the aqueous flow into the eye is reduced by freezing or with a laser (known as cyclodestructive surgery).

Summary
Neovascular glaucoma is an uncommon form of closed-angle glaucoma which can lead to blindness if eye pressure is not lowered. Patients with impaired blood flow to the eye are at particular risk for developing it. Early detection and treatment of the neovascularization may prevent additional loss of vision.