The Many Faces
of Diabetic Retinopathy
Paul Chous, M.A., O.D.
Doctor of Optometry
Type 1 diabetic since 1968
Almost
all health care practitioners are familiar with, or at least
aware of, the importance of diabetic retinopathy (DRT) as a
major complication of both Type 1 and Type 2 diabetes. In fact,
diabetic retinopathy is the leading cause of new blindness for
Americans between the ages of 20 and 74 (past the age of 74,
other age-related eye diseases become more common, and surpass
DRT as major causes of vision loss; most notably, cataract,
glaucoma and age-related macular degeneration.) We know that
retinopathy becomes more likely the longer a person has diabetes,
so that after 10 years, 60% of patients have some retinopathy,
while after 20 years, more than 90% do. We also know that keeping
blood glucose levels as close to normal as possible delays the
onset and progression of retinopathy, based on the findings
of both the DCCT and UKPDS. What readers may be less familiar
with are the various forms/stages of diabetic retinopathy, and
some important differences between these forms.
Background diabetic retinopathy
(BDR) occurs when chronic hyperglycemia damages intra-retinal
capillaries (a process dependant upon several biochemical pathways,
and which results in capillary endothelial pericyte destruction),
causing small amounts of retinal bleeding, as well as protein
and fat exudate within the retina; patients typically have no
symptoms and vision is usually excellent unless the macula is
affected significantly.
Pre-proliferative retinopathy
(PPDR) results when retinal tissue becomes sufficiently ischemic
to initiate release of vaso-proliferative factors. Areas of
ischemic retina are often observable as “cotton wool spots,”
patches of infarcted retinal nerve fiber layer; the caliber
of retinal venules becomes irregular (venous “beading”);
intra-retinal microvascular abnormalities (IRMA) form, and represent
the root system of imminent retinal neovascularization. As with
BDR, vision is normal without macular involvement. Because both
BDR and PPDR manifest, by definition, prior to the onset of
neovascular proliferation, they are often collectively referred
to as non-proliferative diabetic retinopathy (NPDR).
Proliferative diabetic retinopathy
(PDR) occurs when abnormal blood vessels begin to proliferate
on the surface of the retina and optic nerve, leading to a fibrovascular
complex that causes retinal traction, profuse pre-retinal and
vitreous hemorrhage and, in severe cases, retinal detachment
resulting in blindness (traction retinal detachment or TRD).
PDR presents in both subtle and florid fashion, and the combination
of florid optic nerve (“disc”) neovascularization
and vitreous hemorrhage signals the highest probability of visual
loss. The Diabetic Retinopathy Study (DRS) demonstrated that
pan-retinal photocoagulation (PRP – typically one to four
thousand retinal laser burns uniformly applied outside the macula)
reduces the risk of severe vision loss from PDR by 50-75%, probably
by reducing overall retinal hypoxia and inhibiting release of
vasoproliferative factors.
Yet another form of retinopathy
occurs when poorly patent capillaries within the most critical
and sensitive area of the retina, the macula, cause fluid swelling
that interferes with vision, a condition known as diabetic macular
edema (DME). The macula permits good, detail and color vision.
When diabetes or any other disease process damages the macula,
patients lose at least some of their ability to see detail and
perceive color. In fact, diabetic macular edema is the leading
cause of vision loss associated with diabetes, causing visual
impairment at twice the rate as that caused by PDR. More than
100,000 new cases occur in the US each year, and diabetic macular
edema is a leading cause of ‘legal blindness’ (defined
as vision less than 20/200 on the Snellen eye chart with the
use of prescription lenses.) Incredibly, some patients develop
vision threatening DME yet have 20/20 Snellen visual acuity
and no symptoms at the time of diagnosis.
The “Early Treatment of
Diabetic Retinopathy Study” (ETDRS) proved that laser
treatment of vision threatening diabetic macular edema (known
as clinically significant diabetic macular edema or CSDME) reduces
the risk of substantial worsening of vision by about 50%. The
requisite features of CSDME are memorized by every eye doctor
in training, may be appreciated only by three-dimensional, stereoscopic
examination, and are determined by the exact size and location
of macular edema. It is important to understand that DME may
occur alone or with any one of the other three stages of DRT,
a fact that yields six distinct manifestations of DRT.
For all forms of diabetic retinopathy,
the risk of developing vision threatening disease (PDR and CSDME)
is reduced by tight control of blood sugar and blood pressure.
It is also known that dyslipidemia worsens the risk of CSDME
in particular, as does cigarette smoking. Patients must be advised
to keep their quarterly glycosylated hemoglobin (hemoglobin
A –1-c) readings below 7%, their blood pressure readings
less than or equal to 140/80, to work on improving their blood
lipid profiles, and to quit smoking. Most importantly, all diabetics
should have an annual dilated retinal examination by an optometrist
or ophthalmologist experienced with diabetic eye disease; the
sooner DRT is detected, the more can be done to keep it from
robbing your patients of any vision.
In my next segment, we will consider
another common, but often misunderstood manifestation of diabetic
eye disease, glaucoma.
Dr. Paul Chous received his undergraduate
education at Brown University and the University of California
at Irvine, where he was elected to Phi Beta Kappa in 1985. He
received his Masters Degree in 1986 and his Doctorate of Optometry
in 1991, both with highest honors from the University of California
at Berkeley. Dr. Chous was selected as the Outstanding Graduating
Optometrist in 1991. He has practiced in Renton, Kent, Auburn
and Tacoma, Washington for the last 12 years, emphasizing diabetic
eye disease and diabetes education. Dr. Chous has been a Type
1 diabetic since 1968. He lives in Maple Valley, Washington
with his wife and son.
About the Author
Dr.
Paul Chous is the recent author of a critically acclaimed book
for patients and health care providers on diabetes and the eye,
Diabetic Eye Disease: Lessons From A Diabetic Eye Doctor –
How To Avoid Blindness and Get Great Eye Care (Fairwood Press).
He may be reached via his web site at http://www.diabeticeyes.com.
Print
This Article
Paul's
Archives
