By: Dr. Amjad Hammad
One of the most frequent causes of vision impairment in the United States and throughout the rest of the world is diabetic retinopathy. Diabetic retinopathy is a complication of diabetes that causes damage to the blood vessels of the retina – the light-sensitive tissue that lines the back part of the eye, allowing you to see fine detail. Diabetic retinopathy occurs in more than half of the people who develop diabetes. The longer you have diabetes and the less controlled your blood sugar is, the more likely the possibility that you will develop diabetic retinopathy.
There are generally two causes of vision loss from diabetic retinopathy – diabetic macular edema and proliferative diabetic retinopathy.
- Diabetic macular edema. Diabetic macular edema is the term used for swelling in the central part of the retina. The macula, or center part, of the retina is used for sharp, straight-ahead vision. It is nourished by blood vessels that become affected by diabetes. The blood vessels are weakened by diabetes and may become leaky. This causes the retina to become thickened or swollen. It is this swelling of the central part of the retina that can lead to decreased vision.
- Proliferative diabetic retinopathy. Diabetes can cause damage to the small blood vessels in the retina, resulting in poor circulation to the retina. Vision may be lost because some of the retina tissue may die as a result of this inadequate blood supply. Unlike skin tissue, which might grow back if it is lost, retina tissue is like brain tissue and does not grow back once it is lost. Furthermore, the poor circulation may lead to the development of growth factors that can cause new blood vessels and scar tissue to grow on the surface of the retina.
This stage of diabetic retinopathy is called proliferative diabetic retinopathy (PDR). It is referred to as “proliferative” because at this stage of the disease, new, abnormal blood vessels and scar tissue begin to grow on the surface of the retina. The vessels bleed into the middle cavity of the eye, causing vision loss because light cannot reach the retina. In addition, the scar tissue formation can pull on the retina and cause vision loss by detaching the retina from the back of the eye. Occasionally, these blood vessels and scar tissue may grow in the front of the eye, where fluid normally exits. When the fluid cannot escape, pressure can build in the eye, creating a rare type of glaucoma (neovascular glaucoma) that can damage the vision even further and cause the eye to become painful.
It is possible to have diabetic retinopathy for a long time without noticing symptoms. Often, diabetic retinopathy will cause changes unnoticeable to a patient until substantial damage already has occurred.
Diabetic retinopathy usually affects both eyes. Symptoms may include blurred or double vision, difficulty reading, or the appearance of spots – known as “floaters” – in your vision. You also may notice a shadow across your field of vision, pain or pressure in your eyes, or difficulty with color perception. Some patients may experience a partial or total loss of vision.
The primary cause of diabetic retinopathy is diabetes – a condition in which the levels of glucose (sugar) in your blood are too high. Elevated sugar levels from diabetes can damage the small blood vessels that nourish the retina, and may in some cases block them completely. As a result, the blood supply to the retina from these damaged blood vessels is cut off, and vision is affected.
As mentioned above, in response to the lack of blood supply the eye may create growth factors that cause leakage of blood vessels that result in swelling of the retina (diabetic macular edema) or growth of new blood vessels and scar tissue (proliferative diabetic retinopathy). These new blood vessels can bleed into the middle cavity of the eye, and the scar tissue can pull on the retina — sometimes, leading to vision loss if the retina detaches from the back wall of the eye.
Anyone who has diabetes is at risk of developing diabetic retinopathy. There are, however, additional factors that can increase your risk.
One of the most important factors is the duration of your diabetes. The longer you have had it, the greater your risk of developing diabetic retinopathy. Another key factor is how well you have controlled your blood sugar level over time. Another factor that can influence the control of your blood sugar level and the subsequent development of diabetic retinopathy is high blood pressure. It also is possible that cholesterol levels can have an effect on this process, and pregnancy in someone with diabetes can result in changes in the retina as well.
The best way to diagnose diabetic retinopathy is with a dilated eye exam. During the exam, you will receive drops in your eyes to make your pupils dilate (open widely) to allow a better view of the inside of your eye, especially the retina tissue.
During the exam, I will look for swelling in the retina (diabetic macular edema), abnormal blood vessels that may predict an increased risk of developing new blood vessels, and the actual presence of new blood vessels or scar tissue on the surface of the retina (proliferative diabetic retinopathy).
Three other diagnostic tools are also used to detect and manage diabetic retinopathy:
- Fundus photography. I may take photographs of the back of the eye to facilitate detection of diabetic retinopathy as well as to document the retinopathy to make it easier to determine if the condition is worsening at a subsequent visit.
- Fluorescein angiography. To supplement the eye exam, I may conduct a retinal photography test called fluorescein angiography. After dilating your pupils, a dye will be injected into your arm that will circulate through your eyes. It is like a food coloring however, it does not affect the kidneys, and is unlike the dye that is used with MRIs or CAT scans. As the dye circulates, pictures are taken of the retina, allowing me to accurately detect blood vessels that are closed, damaged, or leaking fluid. The pictures are black and white to facilitate the detection of these changes, but the process is not the same as having an x-ray.
Normal eye under Fluorescein Angiography
Diabetic Retinopathy under Fluorescein Angiography
Optical coherence tomography (OCT): I may suggest an optical coherence tomography (OCT) exam. This test provides cross-sectional images of the retina that show its thickness, helping determine whether fluid has leaked into retinal tissue. This latest generation of imaging technology (15 times more sensitive than conventional ultrasound) makes quicker and more accurate diagnoses possible. Instead of using acoustic waves as in ultrasound, OCT uses light to take cross section images of the retina.
Normal eye seen with OCT scan
Diabetic Retinopathy seen with OCT scan
B-Scan ultrasound is most useful when direct visualization of intraocular structures is difficult or impossible. Situations that prevent normal examination include lid problems, severe edema, corneal opacities, dense cataracts or hemorrhage. In such cases, diagnostic B-scan ultrasound can give valuable information on the status of the vitreous and retina.
Treatment and drugs
There now are many treatments for diabetic retinopathy, including lasers to the retina or miniscule injections of medications into the middle cavity of the eye. These procedures can be done in my office to prevent, treat, or reverse damage from diabetes in the retina.
Researchers have shown that eye injections, often but not always in combination with laser treatment, result in better vision than laser treatment alone for diabetes-associated swelling of the retina–the condition known as diabetic macular edema.
The key to these treatments is the blocking by eye injections of a chemical signal in the body that stimulates blood vessel growth, known as vascular endothelial growth factor (VEGF). Repeated doses of anti-VEGF medications may be needed to prevent blood vessels from leaking fluid and causing damage to the eye.
I commonly treat patients with “focal” laser photocoagulation for diabetic macular edema. This occurs in most patients. The laser has been a great tool for preventing additional leakage, thereby preserving visual acuity. At times, there are situations that are not amenable to treatment with laser and we may discuss the possibility of intravitreal (aka intraocular) injections of steroids or anti-VEGF medicines.
Patients who have developed the proliferative phase of diabetic retinopathy may require PRP, or pan-retinal photocoagulation. The laser is used in this instance to treat the peripheral retina. Enough PRP is treated to reverse the neovascular tissue growing along the surface of the retina. Once the proliferative phase of the diabetic retinopathy is arrested, the chance of blindness is dramatically reduced.
With proper examinations, the earliest signs of diabetic retinopathy in the retina can be detected before you have any vision loss.
Regular dilated eye exams with a retina specialist are important, especially when you’re at higher risk for diabetic retinopathy or diabetes. Over the age of 50, an exam every year is a good idea to look for signs of diabetes or diabetic retinopathy before any vision loss has occurred.
Even if not all vision loss from diabetic retinopathy can be prevented or treated at this time, patients usually are able to find ways to live with diminished vision.