|
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.
Figure 1: In neovascular glaucoma, the iris is often
covered by new vessels (arrow). These vessels can grow and eventually block the drainage of fluid through the trabecular
meshwork.
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.
Back to top
| Home
| Glaucoma Medications | Surgery
| Studies |
|
Our
Physicians
| New Patient Information |
Locations
| Links |
| Contact
Us | Glaucoma Information | Privacy
Notice | Website
Map |
Glaucoma Associates of Texas
7150 Greenville Avenue, Suite 300
Dallas, TX 75231
Office: 214-360-0000
Fax: 214-360-0083
Copyright
© Glaucoma Associates of Texas 2000-2003
|
