Diabetic retinopathy is caused by high blood sugar levels damaging the network of tiny blood vessels that supply blood to the retina.
The retina is the light-sensitive layer of cells at the back of your eye. It converts light into electrical signals that are sent to the brain through the optic nerve. The brain interprets the signals into the images that you see.
The retina, like all parts of the body, requires a constant supply of blood to survive. Blood is supplied to the retina through a network of tiny blood vessels.
Over the course of many years, the blood vessels can be damaged by high blood sugar (glucose) levels that may be present in people with poorly controlled diabetes.
How diabetic retinopathy progresses
During the initial stages of retinopathy, the damage is limited to tiny bulges (microaneurysms) in the blood vessel walls. Although these can leak blood and fluid, they do not usually affect your vision.
Gradually over time, the blood vessels that supply the most sensitive part of the retina, called the macula, can become damaged. The macula enables you to distinguish colours and focus your eyes for tasks such as reading and writing.
Damage to the macula can lead to some loss of vision. You may not be able to see objects clearly at a distance, or see things in fine detail, such as the small print in a document.
When retinopathy reaches its most advanced stage, some of the blood vessels that supply your retina will become blocked. To compensate for this, new blood vessels will start to form in an attempt to restore the supply of blood.
However, as the new blood vessels are unstable and prone to bleeding, they can lead to blurred and patchy vision because the bleeding obscures your sight.
Over time, the bleeding can lead to the formation of scar tissue which can pull your retina out of position. This is known as retinal detachment, and it can result in a darkening of vision, floaters and, if left untreated, blindness.
Risk factors
Several factors increase your risk of developing diabetic retinopathy. These are described below.
Length of time you have had diabetes
The longer you have had diabetes, the greater your chance of developing retinopathy.
About 90% of people with type 1 diabetes will have some degree of retinopathy after 10 years of having diabetes symptoms.
For people with type 2 diabetes who do not need to take insulin, about 67% will have some degree of retinopathy after 10 years of having diabetes symptoms.
For people with type 2 diabetes who need to take insulin, about 79% will have some degree of retinopathy after 10 years of having diabetes symptoms.
Blood glucose level
If you have diabetes and your blood glucose level is high, you have a higher risk of developing retinopathy.
Blood glucose levels are measured using the HbA1C test. HbA1C is a form of haemoglobin. This is the oxygen-carrying substance that is found in red blood cells and has glucose attached to it.
Small changes in the levels of HbA1C can significantly affect your risk of developing retinopathy. For example, if you have an HbA1C level of 8%, you are 40% more likely to develop retinopathy than someone with an HbA1C level of 7%.
High blood pressure
If you have diabetes and high blood pressure, your risk of developing advanced retinopathy is increased.
Therefore, taking steps to prevent high blood pressure, such as giving up smoking and cutting down the amount of salt in your diet, can help reduce your risk of developing retinopathy.
Read more about preventing high blood pressure.
