|
The retina is the thin layer
of nerve tissue in the back of the eye that functions
like the film in a camera. It is where the picture is
made inside the eye. It requires a large amount of
circulation of blood to make the pictures. The blood is
brought into the retina through an artery and drains
from the retina by a single vein called the central
retinal vein in the back of the eye. When this vein
becomes blocked, the circulation to the eye slows. This
is called a central retinal vein occlusion. The vein can
be partially blocked and the circulation mildly affected
or more completely blocked with severe damage to the
circulation.
|
|
|
Normal |
|
|
|
CRVO |
When the vein becomes
blocked, the blood cannot exit from the back of the eye,
and so pressure in the circulation results in swelling
in the retina or bleeding into the retinal tissue. If
the vein is more completely blocked, the circulation
slows down, and the eye becomes starved for oxygen and
nutrients. The retina can begin to die. In some patients
with severe blockage, abnormal vessels will start to
grow. These abnormal vessels, instead of helping the
situation, grow in the wrong places and cause further
damage. One of the areas where abnormal vessels can grow
is in the part of the eye that controls the intraocular
pressure. A severe form of glaucoma can result. This
type of glaucoma, called neovascular glaucoma, can
result in severe pain and complete blindness of the eye.
The outlook for a central
retinal vein occlusion can be best predicted by the
vision. If the vision is only mildly affected, usually
the central vein occlusion will remain mild and
sometimes improve without treatment. If the vision is
severely affected, often there is permanent visual
damage, and the risk of the painful form of glaucoma is
higher.
The only proven treatment
for a central vein occlusion is laser treatment if
abnormal vessels start to develop. The laser treatment
can be successful in preventing the severe form of
glaucoma and preventing abnormal vessel growth, but does
not improve the vision.
Because of the grim
visual prognosis in severe central retinal vein
occlusions, other treatments are being tried. One
treatment is a surgery. During surgery, the vitreous gel
is partially removed, and then a small incision is made
adjacent to the central retinal vein in the back of the
eye. This incision may relieve pressure on the vein and
improve the circulation. The surgery has not been proven
by a large clinical trial, but some patients with severe
visual loss have recovered vision. Patients who are
younger, have recent visual loss and have swelling in
the area around the vein may be better candidates for
the surgery.
Another form of treatment
that is being tried is the injection of an
anti-inflammatory steroid medication inside the eye.
This medication can help relieve swelling in the retina
and appears in some patients to improve the vision. It
has not been proven by a large clinical trial, but such
a trial is currently being instituted.
Whether or not treatment
is instituted, most patients with central vein occlusion
are followed periodically for a number of months to
assess the risk of abnormal vessel development and the
possible need for laser treatment. Risk factors for
central vein occlusion include a history of glaucoma, a
history of hypertension, smoking, history of
atherosclerosis, or problems with blood viscosity or
blood clotting.
|
|
