Diabetic retinopathy is a complication of diabetes mellitus (sugar diabetes) that affects the retina of the eye. This is the inner lining of the eyeball which is light sensitive and converts incoming light into electrical impulses. The signals then travel to the brain where it is deciphered and results in the sense of sight. When the retina is diseased, vision is impaired to varying degrees. With diabetic retinopathy, the changes are gradual and progressive. The tiny blood vessels thats supply oxygen to the retina (retinal capillaries) are compromised and results in a number of changes that eventually damage the retina irreversibly.
Causes of Diabetic Retinopathy
Prolonged hyperglycemia (high blood glucose levels) affects the anatomy and function of retinal capillaries. The excess glucose is converted into sorbitol when it is diverted to alternative metabolic pathways. Sorbitol leads to death or dysfunction of the pericytes of the retinal capillaries. This weakens the capillary walls allowing for the formation of microaneurysms, which are the earliest signs of diabetic retinopathy. The weak capillary walls can also be responsible for increased permeability and the exudates.
Due to the predisposition to increased platelet aggregration and adhesion (blood clot formation) as a result of diabetes, the capillary circulation becomes sluggish or even totally impaired by an occlusion. This can also contribute to the development of diabetic retinopathy.
These changes and the progression of the disease can be categorized into two clinical stages :
- Non-proliferative diabetic retinopathy
- Proliferative diabetic retinopathy
Risk Factors for Diabetic Retinopathy
Both type 1 and type 2 diabetics are at risk of developing retinopathy. Long term diabetes and poorly controlled diabetes increases the risk significantly, irrespective of the types of diabetes. In addition, diabetics with hypertension, who are pregnant or have high cholesterol levels (hypercholesterolemia) are at a greater risk.
Symptoms of Diabetic Retinopathy
It is not uncommon for there to be no symptoms in the early stages of diabetic retinopathy (mild non-proliferative stage). Due to the gradual onset of symptoms, many diabetics ignore the early symptoms until it has significantly affected the vision or been diagnosed upon opthalmoscopic examination (fundoscopy).
Many of the symptoms of diabetic retinopathy could also be attributed to other opthalmic complications of diabetes, like glaucoma, cataracts, corneal abnormalities or neuropathy.
Symptoms may vary but the most commonly reported visual disturbances include :
- Blurred vision
- Poor night vision
These visual disturbance should not be mistaken for age-related changes and other causes of problems with visual acuity. Other reported symptoms of diabetic retinopathy include fluctuating and progressive deterioration of vision, dark spots, impairment of color vision and/or reduced peripheral vision. Eventually significant or total loss of vision (blindness) will occur.