Diabetes Mellitus affects the small blood vessels in the body. When diabetes affects the blood vessels of the eye, the vision can range from normal or minimally affected to a severe decrease leading to blindness. Diabetes is the leading cause of new blindness in the 20-64 year old age group. The prevalence of diabetic retinopathy increases with the duration of the diabetes and patient age. The exact cause of the vascular disease is unknown.
Diabetes affects the blood vessels of the retina. The retina is composed of nerves and blood vessels. It lines the back of the eye like film in a camera. The visual information from the retina is transmitted to the brain via the optic nerve. The macula is the area of the retina that is responsible for the central reading vision. The rest of the retina supplies the peripheral vision.
Background Diabetic Retinopathy
Diabetes can cause the retinal blood vessels to leak blood or fluid causing hemorrhages and swelling. In early diabetic retinopathy, the leaking blood vessels can occur outside the macula. A diabetic may not be aware of the retinal changes because the vision is not affected. If the leaking occurs in the macula where the centrtal vision is, the vision becomes blurred. Diabetic retinopathy involving the macula, is the most common cause of decreased vision in a diabetic.
Proliferative Diabetic Retinopathy
More widespread damage to small blood vessels result in decreased blood flow to the retina. Abnormal blood vessel growth will then occur on the surface of the retina and optic nerve. These abnormal blood vessels are fragile and bleed easily. These hemorrhages lead to scar tissue formation, severe decreases in vision, and blindness. In cases of severe proliferative diabetic retinopathy, new blood vessels can grow on the iris. This can result in glaucoma, blindness, and pain.
The relationship between the level of blood glucose and diabetic retinopathy remains unclear.
Laser surgery for diabetic retinopathy involves using the heat of the laser to create tiny scars in the abnormal area of the retina. In cases of background diabetic retinopathy and leakage of abnormal vessels, these laser scars attempt to seal leaking vessels, to stabilize and prevent loss of vision. In cases of proliferative diabetic retinopathy where fragile, abnormal vessels are growing on the surface of the retina and optic nerve, the laser scars attempt to prevent bleeding. Side effects in this type of surgery are decreased night vision and peripheral vision in some patients.
Blood and scar tissue are removed from inside of the eye.
Fluorescein angiography is an office procedure that may be used to further evaluate the extent of the retinopathy. This is a blood flow study of the retinal vessels. A small amount of fluorescent dyd is injected into the arm vein and photographs are taken as it circulates through the retinal vessels. This can highlight abnormal blood vessels and areas of leakage.
The patient may not notice the early vision changes of diabetic retinopathy if the macula is not involved or if the bleeding is not severe. As in most diseases, early detection is important. Yearly routine eye exams are essential for any diabetic whether diet-controlled, on oral medication or on insulin. If diabetic retinopathy is already present, more frequent exams may be necessary.