Diabetic Macular Edema: the Other Diabetic Retinopathy
Variety of complications can plague vision
Many patients with diabetes are familiar with, or at least aware of, the importance of diabetic retinopathy 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 much more common and surpass diabetic retinopathy 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. What readers may be less familiar with are the various forms of diabetic retinopathy, and some important differences between these forms.
Nonproliferative diabetic retinopathy (NPDR) occurs when chronically high blood glucose levels damage the smallest blood vessels (capillaries) within the retina, causing small amounts of retinal bleeding, as well as protein and fat deposits within the retina; patients typically have no symptoms and vision is usually excellent. Proliferative diabetic retinopathy (PDR) occurs when abnormal blood vessels begin to develop and grow (‘proliferate') on the surface of the retina and the optic nerve, leading to tugging (traction) on the retina, a lot of bleeding and, in severe cases, retinal detachment resulting in blindness. Yet another form of retinopathy occurs when leaky blood vessels 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 is the part of the retina that gives us good, detail vision. It is the area where incoming light is brought to a precise focus (either naturally, or with the help of prescription lenses) allowing us to recognize faces, read words or letters on a road sign or printed page, and appreciate colors. When diabetes or any other disease process damages the macula, we lose at least some of our ability to see detail and perceive color. Side (peripheral) vision is not affected, so people with diabetic macular edema are not totally blinded (as can happen with proliferative diabetic retinopathy), but may lose some ability to read, drive, or recognize faces
An Eye Doctor's View of DME
white fluid deposits ("exudates"), at left,
by accumulation of
fluid within the macula
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 proliferative diabetic retinopathy. More than 100,000 new cases occur in the U.S. each year, and diabetic macular edema is a leading cause of ‘legal blindness' (defined as vision less than 20/200 on the eye chart – the letters just smaller than the big E – with the use of prescription lenses.) Diabetic macular edema does not typically cause as profound a loss of vision as does severe, untreated PDR, but it affects substantially more patients. Incredibly, some patients develop vision threatening DME yet have 20/20 vision on the eye chart test and no symptoms at the time of diagnosis.
Treatment of DME may include various medications (very often, cortisone type drugs) as well as laser therapy aimed at cauterizing leaky blood vessels and reducing accumulated fluid within the macula. The "Early Treatment of Diabetic Retinopathy Study" (ETDRS) proved that laser treatment of vision threatening diabetic macular edema reduces the risk of substantial worsening of vision by about 50%. In addition, new medications on the horizon may actually interfere with the biochemical processes that allow retinal blood vessels to become leaky in the first place.
As for all forms of diabetic retinopathy, the risk of developing DME, and the risk of it worsening, are reduced by tight control of blood sugar and blood pressure. It is also known that abnormal blood lipid levels (high ‘bad' LDL cholesterol and triglycerides) worsen DME, as does cigarette smoking. Patients are advised to keep their quarterly glycosylated hemoglobin (hemoglobin A –1-c) readings as close to normal as possible (6.5% or less), their blood pressure readings less than or equal to 130/80, to work on improving their blood lipid profiles, and to quit smoking. Most importantly, all of us with diabetes should have an annual dilated retinal examination by an optometrist or ophthalmologist experienced with diabetic eye disease; the sooner DME is detected, the more can be done to keep it from robbing you of any vision.
For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
Read more about Dr. Chous here.
Visit Dr. Chous' website here.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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