Diabetic retinopathy
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Diabetic retinopathy is retinopathy (damage to the retina) caused by complications of diabetes mellitus, which could eventually lead to blindness. It is an ocular manifestation of systemic disease which affects up to 80% of all diabetics who have had diabetes for 15 years or more.
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Signs and symptoms
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Diabetic retinopathy often has no early warning signs. Even macular edema, which may cause vision loss more rapidly, may not have any warning signs for some time. In general, however, a person with macular edema is likely to have blurred vision, making it hard to do things like read and drive. In some cases, the vision will get better or worse during the day.
As new blood vessels form at the back of the eye as a part of proliferative diabetic retinopathy (PDR), they can bleed (hemorrhage) and blur vision. The first time this happens, it may not be very severe. In most cases, it will leave just a few specks of blood, or spots, floating in a person's visual field, though the spots often go away after a few hours.
These spots are often followed within a few days or weeks by a much greater leakage of blood, which blurs vision. In extreme cases, a person will only be able to tell light from dark in that eye. It may take the blood anywhere from a few days to months or even years to clear from the inside of the eye, and in some cases the blood will not clear. These types of large hemorrhages tend to happen more than once, often during sleep.
Pathogenesis
Small blood vessels – such as those in the eye – are especially vulnerable to poor blood glucose control. An overaccumulation of glucose and/or fructose (Kawasaki et al 2004) damages the tiny blood vessels in the retina. During the initial stage, called nonproliferative diabetic retinopathy (NPDR), most people do not notice any changes in their vision.
Some people develop a condition called macular edema. It occurs when the damaged blood vessels leak fluid and lipids (fat) onto the macula, the part of the retina that lets us see detail. The fluid makes the macula swell, which blurs vision.
As the disease progresses, severe nonproliferative diabetic retinopathy enters an advanced, or proliferative, stage. The lack of oxygen (ischemia) in the retina causes fragile, new, blood vessels to grow along the retina and in the clear, gel-like vitreous that fills the inside of the eye. Without timely treatment, these new blood vessels can bleed, cloud vision, and destroy the retina. Usually, they look like cotton wool spots, or otherwise show up as microvascular abnormalities. Even so, the advanced proliferative diabetic retinopathy (PDR) can remain asymptomatic for a very long time, and so should be monitored closely with regular checkups.
Risk factors
All people with diabetes mellitus are at risk – those with Type I diabetes (juvenile onset) and those with Type II diabetes (adult onset). The longer a person has diabetes, the higher the risk of developing some ocular problem.
During pregnancy, diabetic retinopathy may also be a problem for women with diabetes. It is recommended that all pregnant women with diabetes have dilated eye examinations each trimester to protect their vision.
Investigations
Diabetic retinopathy is detected during an eye examination that includes:
- Visual acuity test: This test uses an eye chart (the Snellen chart) to measure how well a person sees at various distances (i.e., visual acuity).
- Pupil dilation: The eye care professional places drops into the eye to widen the pupil. This allows him or her to see more of the retina and look for signs of diabetic retinopathy. After the examination, close-up vision may remain blurred for several hours.
- Ophthalmoscopy: This is an examination of the retina in which the eye care professional: (1) looks through a device with a special magnifying lens that provides a narrow view of the retina, or (2) wearing a headset with a bright light, looks through a special magnifying glass and gains a wide view of the retina. Note that hand-held ophthalmoscopy is insufficient to rule out significant and treatable diabetic retinopathy.
- Tonometry: A standard test that determines the fluid pressure (intraocular pressure) inside the eye. Elevated pressure is a possible sign of glaucoma, another common eye problem in people with diabetes.
- Digital Retinal Screening Programs: Systematic programs for the early detection of eye disease including diabetic retinopathy are becoming more common. This involves digital image capture and transmission of the images to a digital reading center for evaluation and treatment referral. See Vanderbilt Ophthalmic Imaging Center [[1] (http://www.retinopathyscreening.org/)]
The eye care professional will look at the retina for early signs of the disease, such as: (1) leaking blood vessels, (2) retinal swelling, such as macular edema, (3) pale, fatty deposits on the retina – signs of leaking blood vessels, (4) damaged nerve tissue (neuropathy), and (5) any changes in the blood vessels.
Should the doctor suspect the need treatment for macular edema, he or she may perform a test called fluorescein angiography. In this test, a special dye is injected into the arm. Pictures are then taken as the dye passes through the blood vessels in the retina. This test allows the doctor to find the leaking blood vessels.
Management
There are two major treatments for diabetic retinopathy, which are very effective in reducing vision loss from this disease. In fact, even people with advanced retinopathy have a 90 percent chance of keeping their vision when they get treatment before the retina is severely damaged. Still, the best way of addressing diabetic retinopathy is to monitor it vigilantly and ensure that it does not happen in the first place by careful blood glucose control and limitation of dietary fructose.
These two treatments are laser surgery and vitrectomy. It is important to note that although these treatments are very successful, they do not cure diabetic retinopathy.
Laser Surgery
Doctors perform laser surgery to treat severe macular edema and proliferative retinopathy, usually in a doctor's office or eye clinic. The goal is to create 1 000 - 2 000 burns in the retina with the hope of reducing the retina's oxygen demand, and hence the possibility of ischemia. In treating advanced diabetic retinopathy, the burns are used to destroy the abnormal blood vessels that form at the back of the eye.
Before the surgery, the ophthalmologist dilates the pupil and applies anesthetic drops to numb the eye. In some cases, the doctor also may numb the area behind the eye to prevent any discomfort. The lights in the office are also dimmed to aid in dilating the pupil.
The patient sits facing the laser machine while the doctor holds a special lens to the eye. During the procedure, the patient may see flashes of light. These flashes may eventually create an uncomfortable stinging sensation for the patient.
After the laser treatment, patients should be advised not to drive for a few hours while the pupils are still dilated. Vision may remain a little blurry for the rest of the day, though there should not be much pain in the eye.
Scatter laser treatment
Rather than focus the light on a single spot, the eye care professional may make hundreds of small laser burns away from the center of the retina, a procedure called scatter laser treatment. The treatment shrinks the abnormal blood vessels. Patients may lose some of your side vision after this surgery, but the procedure saves the rest of the patient's sight. Laser surgery may also slightly reduce color and night vision.
A person with proliferative retinopathy will always be at risk for new bleeding. This means that multiple treatments may be required to protect vision.
Vitrectomy
Instead of laser surgery, some people need an eye operation called a vitrectomy to restore vision. A vitrectomy is performed when there is a lot of blood in the vitreous. It involves removing the cloudy vitreous and replacing it with a saline solution made up of salt and water. Because the vitreous is mostly water, there should be no change between the saline solution and the normal vitreous.
Studies show that people who have a vitrectomy soon after a large hemorrhage are more likely to protect their vision than someone who waits to have the operation. Early vitrectomy is especially effective in people with insulin-dependent diabetes, who may be at greater risk of blindness from a hemorrhage into the eye.
Vitrectomy is often done under local anesthesia. The doctor makes a tiny incision in the sclera, or white of the eye. Next, a small instrument is placed into the eye to remove the vitreous and insert the saline solution into the eye.
Patients may be able to return home soon after the vitrectomy, or may be asked to stay in the hospital overnight. After the operation, the eye will is red and sensitive, and patients usually need to wear an eyepatch for a few days or weeks to protect the eye. Medicated eye drops are also prescribed to protect against infection.
References
- The original text of this document was taken from the public domain resource document "Facts About Diabetic Retinopathy", at http://www.nei.nih.gov/health/diabetic/retinopathy.htm See the copyright statement at http://www.nei.nih.gov/order/index.htm, which says "Our publications are not copyrighted and may be reproduced without permission. However, we do ask that credit be given to the National Eye Institute, National Institutes of Health."
- Basic ophthalmology for medical students and primary care residents, 7th edition
- Kawasaki T, Ogata N, Akanuma H, Sakai T, Watanabe H, Ichiyanagi K, Yamanouchi T. Postprandial plasma fructose level is associated with retinopathy in patients with type 2 diabetes. Metabolism 2004;53:583-8. Fulltext (http://www2.us.elsevierhealth.com/scripts/om.dll/serve?retrieve=/pii/S0026049504000320&). PMID 15131761.