The Many Faces of Diabetic Retinopathy

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.