Causes and Risk Factors
Diabetic retinopathy occurs in individuals with diabetes, but there are a number of factors that increase the risk that a diabetic will develop the condition.
People with type 1 diabetes, which is believed to be caused by autoimmune destruction of insulin-secreting cells in the pancreas, are more likely to develop diabetic retinopathy than people with type 2 diabetes (Yau 2012; Kollias 2010).
One of the most important risk factors for diabetic retinopathy, regardless of the type of diabetes, is how well the diabetes is controlled. This is often measured by levels of a protein called hemoglobin A1c or HbA1c, which is representative of blood sugar levels over a 3 to 4 month period. Hemoglobin is the component of red blood cells that transports oxygen. When high blood sugar damages hemoglobin via a process called glycation, the resultant dysfunctional molecules are called hemoglobin A1c. Conventional sources suggest a HbA1c level of 4.8-5.6% or less is normal, and for diabetics, it is typically recommended that HbA1c levels be maintained at or below 6.5-7% (Yau 2012; Zhang 2010; Kollias 2010; LabCorp 2014). For type 1 diabetics, reducing HbA1c levels to 7.2% can reduce the incidence of diabetic retinopathy by 76%. In people with type 2 diabetes, lowering HbA1c levels by 11% led to a decreased need for a treatment called photocoagulation (Kollias 2010). In contrast, Life Extension® recommends that HbA1c concentrations should be kept below 5.7% to optimize health and reduce the risk of several age-related diseases; levels below 5.0% are even more ideal, but this may be difficult for many individuals to achieve.
Longer duration of diabetes, higher blood glucose levels, higher blood pressure, and insulin use are also associated with an increased risk of diabetic retinopathy (Yau 2012; Zhang 2010; Kollias 2010; Bertelsen 2013). Other risk factors include high cholesterol levels, kidney disease, obstructive sleep apnea, smoking, anemia, and major surgical operations or hospitalizations that can affect blood sugar control (Yanoff 2010).
The fine, delicate blood vessels that supply the retina are vulnerable to stress caused by high blood pressure. Hypertensive retinopathy can also be observed in people without a clinical diagnosis of hypertension. Between 2% and 15% of people >40 years of age will have some signs of hypertensive retinopathy (Wong 2004). In a study, non-diabetic African Americans were more likely than non-diabetic whites to develop hypertensive retinopathy; however, they were also more likely to have higher blood pressure levels, which may explain the association (Wong 2003). Aside from a history of elevated blood pressure, patients with a history of stroke or coronary artery disease are more likely to suffer from hypertensive retinopathy (Wong 2003; Wong 2004). Poorly controlled blood pressure and chronic kidney disease were both linked to a higher risk of retinopathy in non-diabetic individuals (Grunwald 2012; Klein 2010).