Diabetes mellitus is a metabolic disorder characterized by insufficient production of insulin. The disease is common from age 40 to 60 but can also occur in children. Between 1 and 2% of the population of the USA are diabetics. Men and women are affected equally.
Insulin is produced by the islet cells of the pancreas. It allows blood sugar (glucose) to enter cells and be metabolized. If insulin production is low the blood sugar rises with the end result being damage to various tissues and organs (e.g. heart, kidney, brain and eyes).
The inner layer of the eye is called the retina. The retina and the optic nerve can be considered to be part of the brain. The retina consists of rods and cones, nerve cells and blood vessels. Its function is to convert light into vision. The most important part of the retina is the tiny central portion called the macula. The macula is what allows you to see 20/20.
When diabetes damages the retina it is called diabetic retinopathy. It is one of the leading causes of blindness in the United States today. It is a known fact that the longer a person has diabetes the greater the chances of developing diabetic retinopathy. Seven percent of diabetics will develop retinopathy after having the disease for less than 10 years.
The retinal abnormalities seen in diabetic retinopathy consist of changes within the retina, in front of the retina and within the vitreous cavity (the jelly that fills the interior of the eye). There are two in which diabetes affects the eye. The first way is called background diabetic retinopathy. The second way is called proliferative diabetic retinopathy.
The very earliest sign of diabetic retinopathy is a microaneurysm which is an out-pouching of a capillary. It appears as a dark red spot. They can appear and later disappear. Microaneurysms can leak blood and lipid (called exudates) into the retina causing macular edema. Diabetic macular edema is the most common cause of visual loss in all diabetic patients.
Hemorrhages within the retina are frequently seen in diabetic retinopathy. These can appear as small “dots” or larger red “blots”.
Cotton-wool spots can also appear. They represent a tiny area of the retina where the blood supply has disappeared.
Any changes that appear in the macula will cause the patient to experience a blurring of vision. If these changes occur outside of the macular area the patient may not notice any change in vision.
In this phase of the disease new (abnormal) blood vessels grow on the surface of the optic nerve and adjacent to retinal blood vessels. The presence of the new vessels means that the retina is ischemic (insufficient blood supply). The incidence of proliferative diabetic retinopathy is directly related to duration of the disease and is more common in juvenile diabetics. The more severe the retinopathy the greater the chance of developing kidney disease.
These new blood vessels (neovascularization) are fragile and can easily bleed in the vitreous jelly of the eye. This is called a vitreous hemorrhage. The patient would note a marked blurring of vision. The hemorrhage can clear up on its own. If it does not a surgical procedure known as a vitrectomy is required to remove the blood. If new blood vessels are left untreated, scar tissue can grow resulting in traction (pulling) on the retina and finally a retinal detachment with resultant severe visual loss.
Diabetics as a whole have a higher incidence than the general population of developing open-angle glaucoma. Patients that have severe proliferative diabetic retinopathy can also develop a severe type of glaucoma called rubeotic (neovascular) glaucoma. New blood vessels grow along the iris and along the drainage channels. This can result in a very high intra-ocular pressure and if left untreated can result in blindness.
The treatment most widely used today for diabetic retinopathy is laser treatment (photocoagulation). To determine if a patient can benefit from laser treatment a test called a fluorescein angiogram must be performed. A vegetable dye, which fluoresces, is injected into a vein in the arm. The dye travels through the blood stream and appears in the retina in a matter of seconds. The patient is seated in front of a camera that has special filters and serial photographs are taken. The resulting angiogram allows the doctor to study the circulation of the retina. Microaneurysms will light-up (fluoresce) and abnormal new blood vessels will leak dye.
Laser treatment has been used to treat both background and proliferative diabetic retinopathy. It’s effectiveness had been proved in national clinical trials.
For treatment of background diabetic retinopathy with leaking micoraneurysms, each micoraneurysm is treated with the laser. For macular edema a grid pattern of laser is used which involves placing laser burns in a circle around the macula. It is known that laser treatment reduces macular edema and preserves vision.
The treatment of proliferative diabetic retinopathy is pan-retinal photocoagulation (“PRP”). About 1200 to 1500 laser burns are applied to the peripheral retina in two to three treatment sessions. Within weeks of treatment the abnormal new vessels start to regress. Side effects of PRP include difficulty with night vision and occasionally the loss of 1 or 2 lines of vision.
In summary, diabetes is a common metabolic disorder of worldwide distribution. It is well known that diabetes in inherited. It is characterized by high blood glucose levels due to a lack of insulin. Good control of blood glucose levels is the best way to avoid retina problems. All diabetics should have a yearly dilated eye examination.
Feel free to take a moment and view this video http://www.aao.org/eye-health/diseases/what-is-diabetic-retinopathy.