Diabetic Retinopathy Without Diabetes
Chances are if you have one, you will have other.
I recently examined a patient who had diabetic retinopathy in both eyes – with multiple, small areas of fluid leakage and bleeding, and abnormal, dilated capillaries (called microaneurysms) in his retinas. He did not report having been diagnosed with diabetes, so after recommending that he be checked for this possibility I was surprised to find out he had been tested the previous month by his family physician, and was told everything was ‘normal.' This very nice gentleman was overweight, being treated for both high blood pressure and high LDL-cholesterol, and had a family history of type 2 diabetes on both sides, so combined with his eye examination findings my index of suspicion was very high.
I phoned his physician to discuss my findings and asked about what blood test(s) had been performed to rule out diabetes. I was told his latest fasting blood sugar reading was 107 mg/dl, or 5.944 mmol (normal is less than 100 mg/dl, or 5.55 mmol), meaning that he has ‘impaired fasting glucose' and what is now called ‘prediabetes,' by definition. The patient's blood pressure and cholesterol appeared to be well-controlled on medication. We decided to have our mutual patient return to his family doctor for further blood glucose testing, specifically an oral glucose tolerance test (OGTT), which involves measuring blood sugar levels at various times after consuming a standardized, sugar-laden drink. A week later I received a report from the family doctor saying that our patient's OGTT results were abnormal (217 mg/dl / 12.055 mmol at 2 hours, normal being less than 140 mg/dl / 7.77 mmol), indicating that he did, in fact, have diabetes.
The Diabetes Prevention Program (DPP), a very important clinical study proving that type 2 diabetes can be prevented or delayed in patients with prediabetes by engaging in regular physical activity (walking 30 minutes daily, five days per week), also found that about 7% of patients with ‘prediabetes' have diabetic retinopathy. This of course begs the question: "can people have a definitive complication of diabetes without actually having diabetes!" The short answer, the logical answer, is "no."
Type 2 diabetes is, in fact, a progressive disorder. Patients typically develop insulin resistance that causes high blood glucose levels after eating (impaired glucose tolerance, which is measured by OGTT) then, over time, insulin resistance in the liver leads to high blood glucose levels in the morning after fasting all night (impaired fasting glucose - which is measured by doing a fasting blood glucose test, the test most commonly done to diagnose diabetes). It can take several years for this progression from impaired glucose tolerance to impaired fasting glucose to occur, so it is totally possible, probable, and predictable that many patients will have type 2 diabetes for some time before it is diagnosed using fasting blood glucose measurements as the metric. It is during this time that high blood glucose levels start damaging the retina so this may explain, at least in part, why some patients develop diabetic retinopathy without having been diagnosed with diabetes. They have it – they (and their physicians) just don't know it.
Consistent with all of this, a recent, exhaustive analysis of three clinical trials involving thousand of patients both with and without diabetes, using gold standard retinal photographs to identify diabetic retinopathy, found a ‘continuous relationship' between fasting blood glucose levels and presence of diabetic retinopathy, with this serious eye disease being present in fully 10% of patients having fasting blood sugar levels below 100 mg/dl / 5.55 mmol (Lancet 2008; 371(9614):736-43). This led the study authors to conclude that "the current FPG (fasting plasma glucose) cutoff of 7.0 mmol/L (126 mg/dl) used to diagnose diabetes did not accurately identify people with and without retinopathy. These findings suggest that the criteria for diagnosing diabetes could need reassessment."
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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