Oxygen delivered through the nose may improve poor
vision caused by diabetic macular edema, fluid buildup in
the part of the eye responsible for central vision,
according to a pilot study by scientists at Johns Hopkins
and the National Eye
Institute.
In a study of five diabetic patients with persistent
macular edema, breathing supplemental oxygen for three
months reduced fluid buildup and swelling in the macula
and, in some cases, improved visual acuity. Researchers
think the therapy could be used in conjunction with laser
treatments that also improve oxygenation in the retina to
provide long-term stability in these patients.
The results were really dramatic," says Peter A.
Campochiaro, senior author of the study and a professor of
ophthalmology and neuroscience at Hopkins'
Wilmer Eye
Institute.
For the study, published in a recent issue of the
journal Investigative Ophthalmology & Visual
Science, the researchers studied nine eyes of three men
and two women, ages 52 to 69, who had type 2 diabetes for
an average of nine years. All patients had received at
least one laser eye treatment. Despite an average of 2.7
treatments per eye, all eyes except one had persistent
edema.
Patients were given four liters per minute of oxygen
delivered by small tubes inserted into their noses and were
instructed to use the oxygen continuously every day for
three months, removing the tube only when taking showers.
They were provided with a stationary oxygen concentrator
for home and portable oxygen tanks to use outside the
home.
After three months, excess thickness of the macula was
reduced by an average of 43 percent in all nine eyes.
Excess thickness of the fovea, the part of the eye
responsible for the sharpest vision, was reduced by 42
percent, and macular volume dropped by 54 percent. In
addition, three eyes improved in visual acuity, with the
ability to see two lines higher on a standard eye chart.
"The likelihood that these measurements would change
by such magnitudes by chance is very small," Campochiaro
says.
Once the oxygen therapy was discontinued, vision
slowly worsened in some eyes. But in four eyes in which
retinal thickness had returned to the normal range while on
oxygen, the improvement was maintained even after oxygen
was stopped. Since these patients all had previous laser
therapy, it is possible that the reduced thickening of the
macula achieved by oxygen allowed the laser to exercise a
stabilizing effect.
Diabetic macular edema affects up to 10 percent of all
patients with diabetes. It is caused when high blood sugar,
through a cascade of events, causes damage in normal
retinal blood vessels and a decrease in the supply of
oxygen and nutrients. Campochiaro and Quan Dong Nguyen, the
principal investigator on the study, hypothesize that the
retina, when faced with a decrease in oxygen, releases
vascular endothelial growth factor, or VEGF, and other
substances that cause retinal blood vessels to become leaky
and ultimately stimulate the growth of new blood vessels.
The leakage of fluid into the macula causes it to become
thickened and results in vision loss.
Supplemental oxygen reduces production of VEGF and
similar proteins, which in turn reduces the amount of
leaking in retinal vessels and lessens the severity of
macular edema. The treatment could reduce the thickness of
the retina before laser treatment, making the laser more
effective and more likely to maintain stability without
supplemental oxygen. Alternately, supplemental oxygen could
be combined with newer treatments that directly target
VEGF. For example, Campochiaro and colleagues also studied
an oral drug that blocks receptors for VEGF, called PKC412,
which was found to significantly reduce macular edema and
improve visual acuity in diabetics. This first
demonstration of directly targeting VEGF was reported by
the researchers in another study published in the March
issue of the journal.
"This confirms that VEGF is a good target for
treatment of diabetic macular edema," Campochiaro says.
Several drugs that antagonize VEGF in different ways
are now being tested in patients with diabetic macular
edema.
The study was supported by the National Eye Institute.
Co-authors were Quan Dong Nguyen, Syed Mahmood Shah,
Elizabeth Van Anden and Jennifer U. Sung, all of Johns
Hopkins; and Susan Vitale, of the National Eye
Institute.
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