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. |
