The Danger
The diabetic is 25 times more likely
to suffer loss of vision than the average non-diabetic person.
Diabetic retinopathy affects 50% of all diabetics; but 90% of those
who have diabetes for over 20 years develop at least some evidence of
retinopathy, almost all type 1 and over 60% of type 2 patients. The
chances of developing retinopathy increase with age in that it is a
direct function of longstanding increased blood glucose levels. In
short, diabetes can make you go blind. Diabetic retinopathy is one of the
microvascular problems associated with diabetes, in that it affects
the tiny microscopic capillaries, blood vessels that supply the
tissues of the eye with oxygen and nutrients necessary for normal
function. To understand the problem, one must first understand the
normal function of the retina, so try to imagine the eye as a movie
theater. In this analogy, the pupil, where light enters the eye,
represents the projector, while the retina, on the interior rear
surface of the eyeball, is the screen. Near the center of the screen
are the macula and fovea, where close-up vision is most acute, and
the outer edges of the screen represent areas of peripheral vision.
Macular Edema In other tissues of the body, fluid
from capillaries flows freely between cells, but the amount of fluid
in retinal tissue is critical to the thickness of the “screen.”
The cells of retinal capillaries are tightly joined to carefully
regulate fluid movement and retinal thickness.
As long as the tiny
capillaries of the retina function properly, the screen stays
flawless, providing a perfect surface on which to project whatever
you see, a clear image picked up by the optic nerve and sent to the
brain. Proper function of these capillaries depends upon normal
amounts of glucose in the blood, which are of course difficult to
maintain for the person with diabetes.
Exposure to blood
glucose levels higher than normal causes these tiny blood vessels to
leak fluid, which then collects in the retinal tissue to cause
swelling. In any other tissue, such slight swelling would probably
go unnoticed, but swelling of the retina even by a fraction of a
millimeter may cause significant distortion of the vision – usually
a blurring that isn’t corrected by one’s usual prescription
lenses. This first stage of
diabetic retinopathy may go completely unnoticed by many diabetics,
as this swelling (or edema) may affect only the outer fringes of the
peripheral vision. Others, though, may notice visual changes even
with daily fluctuations in blood glucose levels, as the edema affects
the macula, where greater detail is focused.
Vascular Closure As the tiny vessels continue to be
exposed to high blood glucose levels, the damage to them becomes more
pronounced, with tendencies toward clogging, either from clots or
from the effects of swelling mentioned above. Such occlusion impairs
their ability to supply the oxygen and nutrients needed by the
retinal tissues, so retinal tissue supplied by occluded vessels
begins to die, causing permanent damage – dead spots of the retina
– blank spots on the theater screen. Occluded vessels can also
bulge (microaneurisms) and even rupture, spilling blood into the
retinal tissue.
These problems typically occur on the
outer edges of the retina, gradually diminishing the peripheral
vision of the victim, who is often totally unaware that he is losing
his sight. They can also occur in the fovea, the center of the
visual field where fine detail is perceived. These areas of damaged tissue are
replaced by fibrous scar tissue rather than functional retinal
tissue. Not only does this leave the blank spot on your theater
screen, the scar tissue tends to contract (like any scar), and this
can cause the retina to loosen its hold on the rear wall of the
eyeball – so the screen actually begins to fall off the theater
wall.
Neovascularization In response to the
lack of sufficient oxygen, the retinal tissue stimulates production
of growth factors that cause new capillaries to be formed in order to
keep up with demand. This is a natural response in all tissues, but
it is exaggerated in retinal tissues, where the new capillaries tend
to proliferate in inappropriate areas, further occluding the field of
vision and even growing out away from the surface of the retina –
dangling from the surface of the theater screen. These new
capillaries are also subject to the effects of high blood glucose
levels, leaking, clogging, and rupturing like others, sometimes
bleeding extensively into the vitreous, the inner part of the
eyeball. When this happens, an ophthalmologist can’t even examine
the retina, as it can’t be seen for the blood. Obviously, if a
physician can’t see in, the victim can’t see out.
What You Can Do No available medication, whether oral
or eye drop, can help in any way. Treatment for all stages in this
disease process is laser photocoagulation, where an ophthalmologist
burns the damaged blood vessels, cauterizing and closing them to
limit the damage they can cause. It is essential to understand that
such treatment can only slow the damage progression – it can’t
improve one’s vision once damage is done. If the retina begins to
detach, more serious and invasive surgery may be necessary, entailing
removal and replacement of the eye’s vitreous in order to attempt
repair of the retinal detachment.
Since these treatment options leave a
great deal to be desired, prevention is by far the best option; and
early detection of retinal changes can ensure that photocoagulation
treatment is most effective. The type 2 diabetic typically has had
elevated blood glucose levels for several years before diagnosis, so
it is essential to get a dilated examination of the retina
immediately upon diagnosis of diabetes and yearly thereafter. Most
of the damage discussed earlier is visible to an optometrist or
ophthalmologist with an ophthalmoscope, but the eyes must be dilated
in order for the outer edges of the retina to be examined.
Finally, nothing is more important
than tight control of blood sugar levels. Maintaining blood glucose
levels as close to normal as possible can greatly reduce the risk of
developing the damage discussed above and reduce the risk of existing
damage progressing to visual impairment.
For more information:
Frequently Asked Questions About
Diabetic Retinopathy:
http://www.preventblindness.org/eye_problems/diabetic_retFAQ.html Diabetic Retinopathy, from Penn
State College of Medicine:
http://www.insulin-free.org/articles/retchange.htm Screening for Diabetic Retinopathy:
http://www.diabetes.org/diabetescare/supplement/s20.htm Lasers and Diabetic Retinopathy,
from the New York Eye and Ear Infirmary:
http://www.nyee.edu/ophthal/ldr.htm
