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Diabetes can affect sight
If you have diabetes melitus, your body
does not use and store sugar properly. High blood-sugar levels can
damage blood vessels in the retina, the nerve layer at the back of the eye
that senses light and helps to send images to the brain. The damage
in retinal vessels to referred to as diabetic retinopathy.
Types of diabetic retinopathy
There are two types of diabetic retinopathy: nonproliferative
diabetic retinopathy (NPDR) and proliferative diabetic retinopathy
(PDR).
NPDR, commonly known as background retinopathy,
is an early stage of diabetic retinopathy. In this stage, tiny
blood vessels within the retina leak blood or fluid. The leaking
fluid causes the retina to swell or to form deposits called exudates.
Many people with diabetes have mild NPDR, which usually
does not affect their vision. When vision is affected it is the
result of macular edema and / or macular ischemia.
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Macular edema is swelling, or thickening, of
the macula, a small area in the center of the retina that
allows us to see fine details clearly. The swelling is caused by
fluid leaking from retinal blood vessels. It is the most common
cause of visual loss in diabetes. Vision loss may be mild to
severe, but even in the worst cases, peripheral vision continues to
function.
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Macular ischemia occurs when small blood
vessels (capillaries) close. Vision blurs because the macula no
longer receives sufficient blood supply to work properly.
PDR is present when abnormal new vessels (neovascularization)
begin growing on the surface of the retina or optic nerve. The main
cause of PDR is widespread closure of retinal blood vessels, preventing
adequate blood flow. The retina responds by growing new blood
vessels in an attempt to supply blood to the area where the original
vessels closed.
Unfortunately, the new, abnormal blood vessels do not
resupply the retina with normal blood flow. The new vessels are
often accompanied by scar tissue that may cause wrinkling or detachment of
the retina.
PDR may cause more severe vision loss than NPDR because it
can affect both central and peripheral vision.
Proliferative diabetic retinopathy causes visual loss in
the following ways:
Vitreous hemorrhage: The fragile new vessels
may bleed into the vitreous, a clear jelly-like substance that
fills the center of the eyes. If the vitreous hemorrhage is small, a
person might see only a few new dark floaters. A very large
hemorrhage might block out all vision.
It may take days, months or even years to resorb the
blood, depending on the amount of blood present. If the eye does not
clear the vitreous blood adequately within a reasonable time, vitrectomy
surgery may be recommended.
Vitreous hemorrhage alone does not cause permanent vision
loss. When the blood clears, visual acuity may return from its
former level unless the macula is damaged.
Traction retinal detachment: When PDR is
present, scar tissue associated with neovascularization can shrink,
wrinkling and pulling the retina from its normal position. Macular
wrinkling can cause visual distortion. More severe vision loss can
occur if the macula or large areas of the retina are detached.
Neovascular glaucoma: Occasionally, extensive
retinal vessel closure will cause new, abnormal blood vessels to grow on
the iris (colored part of the eye) and block the normal flow of
fluid out of the eye. Pressure in the eye builds up, resulting in neovascular
glaucoma, a severe eye disease that causes damage to the optic nerve.
How is diabetic retinopathy diagnosed?
A medical eye examination is the only way
to find changes inside your eye. An ophthalmologist can often
diagnose and treat serious retinopathy before you are aware of any vision
problems. The ophthalmologist dilates your pupil and looks inside of
the eye with an ophthalmoscope.
If your ophthalmologist finds diabetic retinopathy, he or
she may order color photographs of the retina or a special test called fluorescein
angiography to find out if you need treatment. In this test a
dye is injected into your arm and photos of your eye are taken to detect
where fluid is leaking.
How is diabetic retinopathy treated?
The best treatment is to prevent the
development of retinopathy as much as possible. Strict control of
your blood sugar will significantly reduce the long-term risk of vision
loss from diabetic retinopathy. If high blood pressure and kidney
problems are present, they need to be treated.
Laser surgery: Laser surgery
is often recommended for people with macular edema. PDR and
neovascular glaucoma.
For macular edema, the laser is focused on
the damaged retina near the macula to decrease the fluid leakage.
The main loss of vision. It is uncommon for people who have blurred
vision from macular edema to recover normal vision, although some may
experience partial improvement. A few people may see the laser spots
near the center of their vision following treatment. The spots
usually fade with time, but may not disappear.
For PDR, the laser is focused on all parts
of the retina except the macula. This panretinal photocoagulation
treatment causes abnormal new vessels to shrink and often prevents
them from growing in the future. It also decreases the cahnge that
vitreous bleeding or retinal distortion will occur.
Multiple laser treatments over time are
sometimes necessary. Laser surgery does not cure diabetic
retinopathy and does not always prevent further loss of vision.
Vitrectomy: In advanced PDR,
the opthalmologist may recommend a vitrectomy. During this
microsurgical procedure, which is performed in the operating room, the
blood-filled vitreous is removed and replaced with a clear solution.
The ophthalmologist may wait for several months or up to a year to see if
the blood clears on its own before performing a vitrectomy.
Vitrectomy often prevents further bleeding
by removing the abnormal vessels that caused the bleeding. If the
retina is detached, it can be repaired during the vitrectomy
surgery. Surgery should usually be done early because macular
distortion or traction retinal detachment will cause permanent visual
loss. The longer the macula is distorted or out of place, the more
serious the vision loss will be.
Vision loss is largely preventable
if you have diabetes, it is important to
know that today, with improved methods of diagnosis and treatment, only a
small percentage of people who develop retinopathy have serious vision
problems. Early detection of diabetic retinopathy is the best
protection against loss of vision.
You can significantly lower your risk of
vision loss by maintaining strict control of your blood sugar and visiting
your ophthalmologist regularly.
When to schedule and examination
People with diabetes should schedule
examinations at least once a year. More frequent medical eye
examinations may be necessary after the diagnosis of diabetic retinopathy.
Pregnant women with diabetes should
schedule and appointment in the first trimester because retinopathy can
progress quickly during pregnancy. If you need to be examined for
glasses, it is important that your blood sugar be in consistent control
for several days when you see your ophthalmologist. Glasses that
work well when the blood sugar is stable.
Rapid changes in blood sugar can cause
fluctuating vision in both eyes even if retinopathy is not present.
You should have your eyes checked promptly
if you have visual changes that:
When you are first diagnosed with diabetes,
you should have your eyes checked:
Copyright©1998 American Academy of
Ophthalmology®
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