Elevated blood sugar level effect on the eyes
Up to 21% of people with type 2 diabetes have retinopathy when they are first diagnosed with diabetes, and most will eventually develop some degree of retinopathy.
Nearly all patients who have type 1 diabetes for about 20 years will have evidence of diabetic retinopathy.
Obstructive sleep apnea (OSA), retinopathy linked in diabetes
The researchers found that retinopathy was present in more than half—54 percent—of those who had OSA, compared to fewer than a third—31 percent—of those without OSA, independent of the effects of glucose control, age, body mass index, high blood pressure and the duration of the diabetes. This was statistically significant.
In conclusion, diabetic retinopathy including sight threatening complications was found at the time of diagnosis of diabetes in targeted screening group as well as in newly diagnosed diabetics in general practice group.
Retinopathy as diagnosis
"We perhaps should focus less on a single universal cut-off and instead target resources on the basis of standardized, evidence-based, individual risk scores in which measures of glycemia are combined with other risk factors," they suggested.
"But what would we tell our patients when they asked if they had diabetes?" they asked. "We are probably best sticking with what we know until a better alternative diagnostic tool becomes available."
"These results of fasting plasma glucose and retinopathy are therefore consistent with observations that the relation between glucose and macrovascular complications such as cardiovascular disease is continuous with no threshold," Dr. Wong and colleagues concluded, "and is analogous to that of end-organ damage found with other cardiovascular risk factors such as blood pressure and serum cholesterol levels."
The report reviews changes in recommendations for the diagnosis of diabetes during the past 3 decades and presents data on the reliability and validity of fasting plasma glucose and HbA1c testing. In 1979, the National Diabetes Data Group provided diagnostic criteria for diabetes based on the distribution of glucose levels. These criteria were used for almost 20 years. In 1997, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus changed the recommendations to emphasize the relation between glucose levels and the presence of long-term complications (particularly retinopathy) and lowered the fasting plasma glucose level for diagnosing diabetes from 140 mg/dL to 126 mg/dL. Although previous expert committees recommended against using HbA1c values for the diagnosis of diabetes, the current expert committee concludes that the precision and accuracy of HbA1c assays have now been shown to be as accurate as glucose measurements at defining the level of hyperglycemia at which retinopathy begins. In a recent analysis, moderate retinopathy was virtually nonexistent among more than 15,000 subjects with HbA1c levels <6.5%.
This last month, another astounding statistic came forth from the DPP data: Over three years of subsequent follow-up of 302 DPP participants, 13% of prediabetics who developed type 2 disease were found to have diabetic retinopathy, and nearly 8% of “prediabetics” also were found to have diabetic retinopathy, though they never developed diabetes per diagnostic criteria. What do these data mean?
Of course, the meaning of any data set is subject to any and all kind of clinical interpretation and, yes, even philosophical and political “spin.” In my view, there are two key conclusions that emerge. First, that a significant number of newly diagnosed type 2 patients already have microvascular diabetes complications, most probably as a result of chronic hyperglycemic and, possibly, hypertensive insult. This finding is not all that surprising, as a number of previous studies have shown that up to 35% of newly diagnosed type 2 patients will have at least mild, non-proliferative diabetic retinopathy with meticulous fundus examination. A significant corollary to this conclusion is that patients are not being diagnosed and treated early enough; little surprise, here.
The second key conclusion is that patients are suffering end-organ damage even though they don’t conform to diagnostic criteria, even though they “do not have” the disease that causes such end-organ complications.. Logic aside, we are faced with the relatively untenable position of a new diagnostic category – “prediabetic retinopathy.” The more logical corollary here, of course, is that these patients do, indeed, have diabetes.
Diabetic Retinopathy Occurs in Pre-Diabetes
Diabetic retinopathy has been found in nearly 8 percent of pre-diabetic participants in the Diabetes Prevention Program (DPP), according to a report presented today at the American Diabetes Association's 65th Annual Scientific Sessions. Diabetic retinopathy, which can lead to vision loss, was also seen in 12 percent of participants with type 2 diabetes who developed diabetes during the DPP. No other long-term study has evaluated retinopathy in a population so carefully examined for the presence or development of type 2 diabetes.
“These findings reinforce the recommendation that patients with newly diagnosed type 2 diabetes should be screened for retinopathy,” said Emily Chew, M.D., of the National Eye Institute, part of the National Institutes of Health (NIH) under the U.S. Department of Health and Human Services, which funded the study. “We advise good control of blood glucose, blood pressure, and cholesterol as well as regular eye exams.”
“Previous studies have not accurately defined when type 2 diabetes begins, so our understanding of the onset of diabetic eye disease has been limited. Now we know that diabetic retinopathy does occur in pre-diabetes. We’re also seeing it early in the course of diabetes — within an average of 3 years after diagnosis,” noted Richard Hamman, M.D., DrPH, professor and chair, Department of Preventive Medicine and Biometrics, University of Colorado School of Medicine, and vice chair of the DPP. “This adds to our understanding of the development of retinopathy and suggests that changes in the eye may be starting earlier and at lower glucose levels than we previously thought.”
Pre-diabetes is a condition in which blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes. The condition is sometimes called "impaired fasting glucose (IFG)" or "impaired glucose tolerance (IGT)," depending on the test used to diagnose it. People with pre-diabetes have an increased risk of developing type 2 diabetes, heart disease, and stroke.
Diabetic retinopathy, which begins with changes in the small vessels in the back of the eye, often leads to loss of vision. Regular eye examinations to diagnose retinopathy are recommended for patients with diabetes because treatment with laser photocoagulation can often prevent blindness in more advanced cases. Diabetic retinopathy is still the most common cause of blindness in adults. (For more information about diabetic retinopathy, see NEI’s Diabetic Retinopathy: What you should know http://www.nei.nih.gov/health/diabetic/retinopathy.asp).
“Certain retinopathy lesions are considered indicative of the presence of diabetes because they are the first retinal changes to develop in this disease,” explained Dr. Hamman. “Although the retinopathy seen in the DPP participants was at a very early stage and did not affect vision, eye changes typical for diabetes were found in 8 percent of our study population before they developed diabetes. These observations may lead diabetes experts to reconsider the diagnostic thresholds used to define diabetes, which are based on levels of blood glucose associated with the development of eye, nerve and kidney complications of diabetes.”
DPP study chair David Nathan, M.D., of Massachusetts General Hospital, pointed out that the retinopathy results are based on a random sample of only 12 percent of DPP participants, all of whom had impaired glucose tolerance, a form of pre-diabetes, when the study began. “These initial findings confirm what other studies have suggested. The complications of diabetes may begin before diabetes is diagnosed, at least by the current-day standards,” he explained. “Ideally, an expanded study of the remaining 88 percent of DPP Outcome Study participants might enable us to define more appropriate diagnostic thresholds.”
Three hundred two, or about 12 percent, of the DPP Outcome Study participants who had not developed diabetes during the study, and 588 of 876 participants who had developed diabetes, were selected to participate in the retinopathy study, funded by the NEI. To detect diabetic retinopathy, an evaluation of the fundus (inner lining of the eye) was performed with a special camera that provides a detailed look at the retina. Small changes in the vessels, called microaneurysms and hemorrhages, signal the development and degree of retinopathy severity.
Participants with pre-diabetes and retinopathy typically had a small number of microaneurysms in the eye characteristic of early, mild retinopathy that is not yet linked to vision loss. Those who had developed diabetes in the previous 1 to 5 years had slightly more severe retinopathy. Higher average blood glucose levels and higher blood pressure were associated with the risk of developing retinopathy in the new-onset diabetic patients, similar to previous findings in people with longstanding diabetes who develop retinopathy.