Diabetic retinopathy is due to changes in blood circulation that occur in people with diabetes (above all, when they have a high blood sugar level). These changes damage the blood vessels in the retina which leads to bleeding, fluid leaks and the accumulation of fat.
The damage to these vessels means some areas of the retina receive an insufficient blood supply (ischaemia), while other areas accumulate the fluid leaking from the broken vessels (oedema).
The parts of the retina with broken blood vessels produce a series of molecules (e.g., vascular endothelium growth factor, VEGF) to promote the growth of new vessels. Unfortunately, these molecules generate poorly formed vessels (in a process called neovascularisation) which may bleed and cause vision loss. Furthermore, the accumulation of fluid in certain areas of the retina, particularly in the centre (macula), will result in direct vision loss.
Besides high sugar levels, factors such as increased blood pressure or abnormal cholesterol contribute to the appearance of retinopathy. Patients are also known to present small signs of inflammation and nerve damage in the eye fundus at the very onset of this condition.
Risk factors associated with Diabetic Retinopathy
The main risk factors related to diabetic retinopathy are classed as either modifiable (control over blood sugar levels, blood pressure, high lipid levels [dyslipidaemia] and lifestyle habits) or nonmodifiable (duration of diabetes, age, genetic predisposition and ethnicity).
Duration of diabetes. The risk of developing diabetic retinopathy, or of it progressing further, increases with time. A history of more than 10 years of diabetes is associated with a greater frequency of diabetic retinopathy.
Blood sugar control. Strict glycaemic monitoring (blood sugar levels) with well-controlled glycosylated haemoglobin (HbA1C) values reduces the incidence of retinopathy. Higher blood sugar levels translate into increased glycosylated haemoglobin production. Therefore, glycosylated haemoglobin levels indirectly help measure the effectiveness of the diabetes treatment and provide an indication of the patient’s blood sugar levels over the last 2 or 3 months.
High Blood Pressure. Stable control over blood pressure slows the progression of diabetic retinopathy. Ideally, most people with diabetes should have a blood pressure of less than 140/80 mmHg, although a different target value may be more appropriate depending on the patient.
Blood lipid levels (dyslipidaemia and hypercholesterolaemia). A high level of lipids (cholesterol and triglycerides) in the blood can lead to a greater accumulation of exudates, which are deposits of proteins filtered in the retina. This condition is associated with a greater risk of moderate vision loss.
Microalbuminuria and diabetic nephropathy. Microalbuminuria is related to a protein known as albumin, which could be evidence of diabetic retinopathy when detected in the patient’s urine. The condition is indicative of an emerging kidney problem; despite a lack of clinical manifestations, it is a common comorbidity of diabetes and/or high blood pressure.
Pregnancy. Patients with diabetes and a normal fundus of the eye at the start of their pregnancy have a low risk of developing diabetic retinopathy. However, women who already have retinopathy when they get pregnant can experience progression due to functional alterations in the retina occurring during their pregnancy.