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Diabetic Retinopathy
A Leading Cause of New Blindness
In general, most diabetics, whether Type I or Type II, do exhibit some degree of diabetic retinopathy in their lifetime. I have been in practice for 15 years and have only seen a handful of patients with diabetes over 30 years that do not exhibit any degree of diabetic retinopathy. While the visual results can be devastating, they need not be with routine examination. By the way, it is important to remember that good serum glucose control does not directly correlate with the eye disease, that is, good sugar control does not mean there will be no eye disease. In general, a patient with perfect vision may not know that he or she needs treatment, that is, vision has nothing to do with the level of disease.
The most common situation in diabetic retinopathy is swelling in the macula, a.k.a. macular edema, from leaking blood vessels. Small abnormalities in the blood vessels are called microaneuryms and leak the fluid portion of blood. Occasionally bleeding may be associated. Clinically, doctors examine the retina and look for signs of diabetic retinopathy such as swelling, edema, exudates and bleeding. The mainstay of treatment for diabetic macular edema (aka clinically significant macular edema) is laser photocoagulation. The goal is to periodically treat the macular area to prevent further worsening of the swelling. At times, the vision may improve. I caution against expecting tremendous improvement as this is a lifelong process.
Fewer patients develop the more aggressive phase of the disease. Proliferative diabetic retinopathy is a stage that presents when significant retinal ischemia develops, that is, the retina does not receive enough oxygen as the blood supply is compromised by longstanding diabetes. As a result, abnormal vessels, or neovascularization, develop on the surface of the retina and other eye structures. VEGF has been identified as the growth factor causing neovascular growth in response to inadequate oxygen/blood supply to the retina. As ivy grows on the forest floor, the neovascular complexes can spread on the retina and eventually cause a retinal detachment. Neovascularization can also plug the normal drainage mechanisms of the eye causing neovascular glaucoma. These two mechanisms are the major pathways to blindness in diabetics.
If there are signs of proliferative diabetic retinopathy (PDR), panretinal photocoagulation is the treatment of choice. In this scenario, laser is applied to the peripheral retina in an attempt to reduce oxygen demands. At some point, oxygen demands will be lowered enough so that VEGF is no longer produced. This usually results in clinical stabilization of the disease.
No one can determine who will develop proliferative diabetic retinopathy. Routine examination is crucial to preventing vision loss. At the very least newly diabetics need a dilated exam on an annual basis. Those patients that exhibit little or no diabetic retinopathy may be seen on an annual basis. More high risk patients will require more frequent visits to the office. Treatment is highly effective in preventing vision loss and less effective in improving vision (if some were lost). As I hinted above, good vision does not correlate with the severity of disease. In other words, you may have 20/20 vision, but may still have proliferative disease.