Diabetic retinopathy is a complication of long-standing diabetes that affects vision. It describes damage to the retina, the light-sensitive layer at the back of the eye that is responsible for transmitting nerve impulses to the visual centres in the brain via the optic nerve.
Diabetes mellitus is characterized by a persistent high blood sugar level. This can eventually damage the small blood vessels that supply the retina with nutrients and oxygen. The retina is then starved of vital nutrients as well as being potentially exposed to leakage from the damaged blood vessels which can blur vision. Without treatment, diabetic retinopathy can lead to a complete loss of vision.
Pathology of diabetic retinopathy
The retina lies at the back of the eye and is provided with a supply of blood vessels and nerves. In the initial stages of diabetic retinopathy, the blood vessels that supply the retina develop tiny swellings called microaneurysms which are prone to hemorrahge.
In addition, the interruption to the supply of nutrients and oxygen triggers the formation of new blood vessels across the eye. However, these new blood vessels are brittle and also prone to breakage. Both the microaneurysms and the new blood vessels may rupture causing the leakage of blood into the retina and blurred vision.
Eventually, new blood vessels, aneurysms and scarring may occur all over the retina, including the central part of the retina called the macula which is responsible for central vision. This can cause a reduction in eye sight or in more advanced cases, a complete loss of vision.
Symptoms of diabetic retinopathy
In the early stages, there may be no symptoms of diabetic retinopathy and the condition may go unnoticed. If symptoms are present, they may include:
"Floaters" or shapes that float in the visual field
Difficulty seeing in dim light or at night
Sudden loss of vision
Diagnosis, screening and treatment
Blindness caused by progressive retinopathy cannot be reversed so it is important to prevent progression in the early stages. All diabetics aged 12 years or more need to be screened for diabetic retinopathy annually. The retina is visualized using an ophthalmoscope or fundoscope and angiography may be used to confirm a diagnosis.
Treatment for retinopathy depends largely on the stage of the condition. In the early stages, stringent control of blood sugar levels is one of the best ways to treat the condition. In more advanced cases, laser surgery of the retina may be recommended.
Reviewed by Sally Robertson, BSc