Retinal Artery Occlusion
The
retina, the
light sensitive tissue that lines the back of the
eye, is nourished by a fragile network of blood
vessels including arteries and
veins. The
arteries carry important oxygen and nutrients to the
eye where they are distributed out into the retinal
tissues through a complicated meshwork of arterioles
and capillaries. These nutrients are vital to
the health and function of the retina. See "Eye
Anatomy"
When an artery becomes blocked, it is termed a
retinal artery occlusion. Retinal arteries can
become blocked by emboli, sometimes cholesterol or
calcium plaques, that travel up the artery with the
blood flow and become lodged where the artery or
arteriole narrows. These emboli are often
related to cardiovascular disease. Once this clogging occurs,
the vital oxygen and nutrients are reduced or cut
off from the retina that was supplied by the artery
and the retina starves.
There are two types of retinal artery occlusions:
branch retinal artery occlusion and central
retinal artery occlusion.
Branch retinal artery occlusion (BRAO)
The smaller extensions off the main retinal artery
are called "branches". When a branch retinal
artery becomes blocked, the retinal tissue that the
branch artery supplies can be damaged, resulting in
loss of vision. Edema and ischemia can occur
and injury to the
retina tissue is often permanent.
Typically, acute loss of vision is limited, to
confined areas of the retinal and about 85% of eyes
recover to 20/40 or better vision.
BRAO typically affects those over the age of 70.
It is very rare in patients younger than 30, this is
probably attributed to its link to cardiovascular
disease.
Central retinal artery occlusion (CRAO)
The central retinal artery is the main blood supply
to the retina. This main artery is actually
fed by the ophthalmic artery which branches of off
the carotid artery.
If an emboli lodges
in the central retinal artery, the vision loss is
profound in most cases. When obstruction
occurs, it can take as little as 15 minutes for the
retinal tissues to become ischemic and damaged.
Because the blockage takes place in the main artery
that supplies blood to the retina (as opposed to a
smaller branch artery), CRAO is more serious than
BRAO. Vision loss usually ranges from as good
as counting fingers to as bad as light perception
only.
There is no
well-proven treatment for central retinal artery
occlusion with any high percentage of success.
If the patient is in the doctor's office quickly
after the occlusion occurs, the doctor may attempt
to massage the eyeball. This technique is
often used to dislodge the embolus in hopes that it
will travel further "downstream" in the blood
vessel. The further downstream, the less of
the retina that is affected, thus a smaller area of
vision loss. Another
way to promote downstream movement of the embolus is
to perform paracentesis. This involves
inserting a tiny needle into the eye's anterior
chamber (space behind the
cornea and in front of the
iris) and removing a small portion of the eye's
natural fluid. This procedure will lower the
eye's intraocular pressure and, theoretically, allow
temporary increased blood flow in the retinal
arteries, thus pushing the embolus further up the
artery. Some doctors
also believe breathing into a paper bag can slightly
dilate the retinal vasculature, promoting embolus
movement.
None of the
above-described procedures should be performed
without the direction of a physician.
Related links:
Retinal Vein
Occlusion |
