Clemson Eye - Diabetic Eye Disease

Diabetic Eye Disease

WHY ARE EYE EXAMS IMPORTANT IN DIABETES?

Diabetes is a common disease in the United States, and diabetic eye disease is the most common cause of blindness in the US. Regular eye examinations are important in diabetes because diabetic eye disease and the vision loss caused by it are completely preventable.

In diabetes, high sugar levels in the blood damage blood vessels throughout the entire body. Damage to blood vessels in the kidneys can cause kidney failure requiring dialysis. Damage to blood vessels in nerves can cause neuropathy. Your eye also has many blood vessels in it, and diabetes can also damage those blood vessels. In particular, high blood glucose levels cause damage to the blood vessels in the retina of the eye. The retina lines the back of your eye like wallpaper, and is like the film in a camera—it detects the light entering your eye and turns it into pictures for your brain to see. When the retina’s blood vessels are damaged, the retina stops working properly, and sight can be lost.

After being exposed to high sugar levels for a long time, the blood vessels in the retina develop some weak spots. These weak spots often pooch out like bubbles along the blood vessels, and these are called microaneurysms. Sometimes the microaneurysms rupture, and blood spills into the retina to form small dot hemorrhages. Your retina will eventually clear the blood away, but some debris is often left behind—these clumps of debris are called hard exudates. Altogether, these changes—microaneurysms, dot hemorrhages, and hard exudates—are called background diabetic eye disease. Most people with diabetes get these small changes in their eyes after having diabetes for 10 years or more. Background diabetic eye disease does not usually cause significant vision loss unless the swelling occurs in the very center part of the retina, called the macula. If you have swelling here, it is called diabetic macular swelling, and it is a common cause of vision loss among diabetic patients.

Background diabetic retinopathy is a sign that your retina’s blood vessels are sick. If enough of the blood vessels rupture, the retina may not receive enough blood to keep it healthy. In this case, the retina will try to grow new blood vessels to replace the sick ones. Unfortunately, these new blood vessels usually grow in the wrong places. They are fragile, and they break easily, sometimes spilling enough blood to fill up the eye. When these new blood vessels begin to grow, it is called proliferative diabetic eye disease. Proliferative diabetic eye disease is less common than background diabetic eye disease, but is much more likely to take away some or all of your vision.

If it is caught early—before your vision is damaged—proliferative diabetic eye disease can be treated with laser therapy to save your vision. Once the vision is lost, it is very hard to get it back.

Background and early proliferative diabetic retinopathy have no symptoms. The only way to know if you have these changes—and need laser therapy to save your sight—is to visit your eye doctor regularly. People with diabetes should have their eyes examined at least once a year to make sure they do not have early damage that threatens their vision.

Diabetes and Your Vision

Natural History: The prevalence of all types of retinopathy in the diabetic population increases with the duration of diabetes and patient age. Immediately after diagnosis of insulin dependent diabetes mellitus no retinopathy is present. After 7 years 50% of patients and after 17-25 years 90% have some degree of retinopathy. The prevalence of proliferative retinopathy is 26% after 26-50 years duration of diabetes. Systemic hormonal changes occurring at puberty result in increased prevalence of retinopathy after 13 years of age.

Most patients with diabetes ultimately develop characteristic abnormalities of the retinal blood vessels. The earliest stages are characterized by leakage of the normally impermeable retinal vessels. These capillaries begin to leak proteins, complex carbohydrates and lipids that can lead to fluid accumulation (edema) in the retina. If there is enough leakage into the macula – the small area of the retina responsible for sharp central vision – visual acuity is reduced. The earliest manifestations of this non-proliferative retinopathy are microaneurysms, dot and flame-shaped hemorrhages, and lipid exudates. Later, vascular closure causes ischemic damage due to
interruption of blood flow to the retina. In the more advanced stages, fragile new vessel proliferation (neovascularization at the optic disc [NVD] and neovascularization elsewhere on the retina [NVE]) can result in bleeding into the retina and vitreous, fibrous tissue growth, and ultimately retinal detachment, neovascular glaucoma and blindness.

The cause of diabetic microvascular disease is unknown. A number of metabolic consequences of high blood sugar and their relationship to the tissue changes observed in diabetic retinopathy are being investigated. These may lead to the development of new forms of treatment for diabetic patients.

Diagnosis: Much of the blinding complications can be prevented if the retinopathy is detected early enough for treatment with laser photocoagulation surgery. The optimal time for treatment is before the patient experiences visual symptoms. Unfortunately, Because visual loss is often a late symptom of advanced retinopathy, many patients remain undiagnosed and are examined only after the optimal time for treatment has passed.

The diagnosis begins with an accurate history and a comprehensive eye evaluation. Symptoms common in patients with diabetic retinopathy include blurring or distortion of vision, especially with blood sugar elevation, difficulty with night vision or reading, and floaters. It is important to note the duration of disease, as this is the principal factor associated with vision-threatening retinopathy. The degree of blood glucose control also influences the time of onset and rate of progression of retinopathy (as well as nephropathy and neuropathy) in Type I patients. Other systemic diseases can be associated with diabetes. For example, hypertension is present in 22% of Type I and 58% of Type II diabetic patients.

A comprehensive eye evaluation, which includes a dilated retinal examination, is essential. Ancillary tests may be required depending on the severity of retinopathy discovered. These include color fundus photography, fluorescein angiography, and ultrasonography.

Treatment: Three major clinical trials have conclusively demonstrated the value of argon laser photocoagulation surgery in reducing the rate of severe visual loss in patients with advanced diabetic retinopathy as well as in earlier stages of the disease and for the treatment of macular edema. Earlier surgery for severe proliferative retinopathy and vitreous hemorrhage has also been recommended.

The aforementioned clinical trials have shown that individuals who are treated appropriately are more likely to have better visual outcomes than those who are not. Panretinal scatter photocoagulation using the Argon laser reduces the rate of severe visual loss by over 50%. In this outpatient procedure laser light is directed into the eye through a special contact lens held on the eye while the patient sits at a slit lamp. Between 1000 and 2000 burns a fraction of a millimeter in size are evenly placed across the entire peripheral retina This destruction of retinal tissue causes the proliferating vessels to disappear by a poorly understood mechanism. Laser treatment of clinically significant macular edema also reduces the rate of subsequent visual loss substantially. In this case the leaking microaneurysms are treated directly with the argon laser to seal them and allow the edema to be resorbed preventing further vision loss. Vitrectomy and retinal detachment surgery may become necessary in cases of persistent, non-clearing vitreous hemorrhage and for traction retinal detachment due to scarring.

Although diabetes cannot be prevented, in many cases the blinding complications can be moderated. Unfortunately, many diabetic patients are not managed appropriately. Many high-risk eyes do not receive laser therapy. One study showed that 11% of Type I and 7% of Type II patients with high-risk retinopathy had not been seen by an ophthalmologist within 2 years. Table 1 shows the recommended schedule for initial and follow-up examinations based on time of onset of diabetes.

Table 1 Recommended Eye Examination Schedule
Age of onset of Diabetes Mellitus	Recommended Time of First Exam	Routine Minimum Follow-up*
0 – 30	5 years after onset	Yearly
31 and older	At time of diagnosis	Yearly
Prior to pregnancy	Prior to conception or early in first trimester	3 months

Source: American College of Physicians, American Diabetes Association, American Academy of Ophthalmology: Screening guidelines for diabetic retinopathy, Clinical Guideline. Ophthalmology 1992; 99:1626-1628.
*Abnormal findings will dictate more frequent follow-up examinations.

Conclusion: In most patients, diabetic retinopathy can be treated successfully with new and refined laser and surgical methods. Unfortunately, many diabetic patients come to medical attention after they have already experienced visual loss when it is often too late for effective treatment. As diabetes becomes more prevalent in the population screening will prove to be an important cost-effective way to reduce the incidence of its devastating blinding complications.

Related Links:

American Diabetes Association
www.diabetes.org

National Eye Institute
www.nei.nih.gov/health/diabetic/retinopathy.asp