Diabetic retinopathy is a complication of diabetes that affects the retina in the eye. The retina contains the cells that are responsible for our vision. Patients may not show any symptoms during the early stages of diabetic retinopathy but various vision abnormalities such as distorted and blurred vision appear as the disease progresses. Retinopathy is the leading cause of blindness in patients suffering from diabetes. It usually arises in the elderly since it occurs with long standing and poorly controlled diabetes. The damage occurs over many years and even decades before it can lead to blindness.
Diabetic retinopathy develops in the following two stages:
This initial stage is characterized by the weakening of the tiny blood vessels of the retina. The weakened vessels become enlarged at points (microaneurysms) and this is the earliest clinical sign of retinopathy that can be detected in an eye examination. The enlarged vessels then start leaking blood (retinal hemorrhage) and fluids (exudates) into the eye chamber in front of the retina. The deposition of these exudates leads to the thickening of the retina.
This advanced stage is characterized by growth of new capillaries (neo-vascularization) on the retina. The newly formed blood vessels are also weak and start leaking blood into the eye (vitreous hemorrhage). The bleeding can lead to scar formation. Subsequent contraction of the fibrous scar tissue along with the fluid in the eye chamber could lead to detachment of the retina from the back of the eye, thereby causing serious vision impairments. The vision loss is sudden, painless, and severe.
The increase in blood pressure and blood glucose level in diabetes determines the severity of retinopathy. Pregnancy can also worsen retinopathy by impairing blood glucose levels. However, the exact mechanisms by which diabetes causes retinopathy are not clear.
Increased blood glucose level results in increased synthesis of alcohols, like sorbitol, in some tissues. Sorbitol seems to impair the functioning of the cells in capillary walls and regulate the blood flow. Sluggish blood circulation in retinal blood vessels can then contribute to retinopathy.
Hypoxia (lack of oxygen) resulting from blocked blood vessels in the eye is thought to stimulate new blood vessel formation in proliferative retinopathy. In addition, growth hormone is also thought to contribute to retinopathy because destruction of pituitary gland reverses diabetic retinopathy.
Since there is no cure for diabetic retinopathy, patients should get their eyes tested at least once a year to detect the disease before it irreversibly damages the retina. The first line of treatment involves normalizing blood glucose and blood pressure levels. Surgery, laser treatment and medicines are then recommended based on the stage of the retinopathy. Laser treatment to seal off leaking blood vessels and surgical removal of the vitreous fluid (vitrectomy) of the eye could prevent vision loss if done before the retina is severely damaged. Medicines for treating diabetic retinopathy are injected directly into the eye.