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Diabetic retinopathy, the most common diabetic eye disease, is caused by changes in the blood vessels of the retina. There are two types of diabetic retinopathy: background or nonproliferative diabetic retinopathy (NPDR); and proliferative diabetic retinopathy (PDR).
Nonproliferative Diabetic Retinopathy (NPDR)
Nonproliferative diabetic retinopathy (NPDR) is the earliest stage of diabetic retinopathy. With this condition, damaged blood vessels in the retina begin to leak extra fluid and small amounts of blood into the eye. Sometimes, deposits of cholesterol or other fats from the blood may leak into the retina.
NPDR can cause changes in the eye, including:
– microaneurysms – small bulges in blood vessels of the retina that often leak fluid.
– retinal hemorrhages – tiny spots of blood that leak into the retina (these spots alone are rarely responsible for any loss of vision).
– hard exudates – deposits of cholesterol or other fats from the blood that have leaked into the retina.
Many people with diabetes have mild NPDR, which usually does not affect their vision. However, if their vision is affected, it is the result of macular edema and macular ischemia.
– Macular edema is swelling or thickening of the macula. It is caused by fluid leaking from the retina’s blood vessels. The macula, which is responsible for our clear, central vision, does not function properly when it is swollen. Macular edema is the most common cause of vision loss in diabetes. Vision loss may be mild to severe, but in many cases, your peripheral (side) vision remains. Laser treatment may help to stabilize vision.
– Macular ischemia occurs when small blood vessels (capillaries) close. Your vision blurs because the macula no longer receives enough blood to work properly. Currently, there is no effective treatment for macular ischemia.
Proliferative diabetic retinopathy (PDR) occurs when abnormal blood vessels begin to grow on the surface of the retina or optic nerve. This is called neovascularization. PDR mainly occurs when many of the blood vessels in the retina close, preventing enough blood flow. The retina responds by growing new blood vessels in an attempt to supply the area where the original vessels closed. However, the new blood vessels are abnormal and do not supply the retina with normal blood flow. The new vessels are also often accompanied by scar tissue that may cause the retina to wrinkle or detach.
PDR may cause more severe vision loss than NPDR because it can affect both central and peripheral vision.
PDR causes vision loss in the following ways:
– Vitreous Hemorrhage. The delicate new blood vessels may bleed into the vitreous—the gel in the center of the eye—preventing light rays from reaching the retina. If the vitreous hemorrhage is small, you may see a few new, dark floaters. A very large hemorrhage might block out all vision, allowing you to perceive only light and dark. Vitreous hemorrhage alone does not cause permanent vision loss. When the blood clears, your vision may return to its former level unless the macula has been damaged.
– Traction Retinal Detachment. With PDR, scar tissue from neovascularization can shrink, causing the retina to wrinkle and pull from its normal position. This is called traction retinal detachment. Macular wrinkling can distort your vision. More severe vision loss can occur if the macula or large areas of the retina are detached.
– Neovascular Glaucoma. Occasionally, if a number of retinal vessels are closed, neovascularization can occur in the iris (the colored part of the eye). In this condition, the new blood vessels may block the normal flow of fluid out of the eye. Pressure builds up in the eye, resulting in neovascular glaucoma, a particularly severe eye disease that causes damage to the optic nerve.
Diabetes can cause vision in both eyes to change, even if you do not have retinopathy. Rapid changes in your blood sugar alter the shape of your eye’s lens, and the image on the retina will become out of focus. After your blood sugar stabilizes, the image will be back in focus. You can reduce episodes of blurred vision by maintaining good control of your blood sugar.
The best treatment is to prevent the development of retinopathy. Strict control of your blood sugar will significantly reduce the long-term risk of vision loss. Treatment will not usually cure diabetic retinopathy or restore normal visual acuity, but it may slow the progression of visual loss. Without treatment, diabetic retinopathy progresses steadily from minimal to severe stages.
The laser is a very bright, finely focused light. It passes through the clear cornea, lens and vitreous without affecting them in any way. Laser surgery shrinks abnormal new vessels and reduces macular swelling. Treatment is often recommended for people with macular edema, proliferative diabetic retinopathy (PDR) and neovascular glaucoma.
Laser surgery is usually performed in an office setting. For comfort during the procedure, an anesthetic eyedrop is often all that is necessary, although an anesthetic injection is sometimes given next to the eye. The patient sits at an instrument called a slit-lamp microscope. A contact lens is temporarily placed on the eye in order to focus the laser light on the retina with pinpoint accuracy.
For macular edema, the laser is applied near the macula in order to reduce fluid leakage. The main goal of treatment is to prevent further loss of vision by reducing the swelling of the macula. It is uncommon for people who have blurred vision from macular edema to recover normal vision, although some will experience partial improvement.
A few people may see laser spots near the center of their vision following treatment. They usually fade with time, but may not disappear completely.
In PDR, the laser is applied to all parts of the retina except the macula (called PRP, or panretinal photocoagulation). This treatment causes abnormal new vessels to shrink and often prevents them from growing in the future. It also decreases the chance that vitreous bleeding or retinal distortion will occur. Panretinal laser has proven to be very effective for preventing severe vision loss from vitreous hemorrhage and traction retinal detachment.
Side effects of panretinal laser surgery may include:
– temporary blurred vision for days to a few weeks;
– occasional mild loss of central vision;
– mild to moderate loss of peripheral vision;
– decreased night vision.
Multiple laser treatments over time may be necessary. Laser surgery does not cure diabetic retinopathy and does not always prevent further loss of vision. In spite of laser surgery, some people with PDR develop macular distortion or bleeding into the vitreous, causing blurred vision. Vitreous hemorrhage may recur and blood may accumulate faster than the eye can reabsorb it.
Diabetes is a disease which can be controlled but not cured. Early diagnosis of diabetic retinal diseases, close followup care, and lifetime monitoring are key in maintaining good vision.Dr. Raymond M. Girgis is trained to treat diabetic retinal diseases. With his background in Internal Medicine, Dr. Girgis is uniquely qualified in the evaluation and treatment of this disease. In many cases, the treatment can be successfully achieved with retinal laser procedures. In more advanced cases, surgical operations must be performed.