Diabetes mellitus is a disease which presently affects over 200 million people worldwide, a number expected to increase to 350 million by the year 2025. The majority of patients have diabetes type 2, sometimes called adult-onset diabetes, in which the body’s cells become insensitive to insulin. Without this hormone, they are unable to absorb and properly metabolize glucose, the sugar molecule which fuels our organs. Type 1, or juvenile, diabetes is an autoimmune disorder in which the pancreatic cells responsible for the production of insulin are destroyed, limiting the amount of insulin which can be produced. The end result of either type of diabetes is the body’s inability to effectively fuel its organs, as well as the buildup of glucose and other metabolites throughout the tissues. Damage to multiple organs, including the eyes, can occur without proper treatment.
Diabetes affects the eyes in a number of ways. The first problem new diabetics with elevated blood sugar often notice is blurring or fluctuating vision. This is caused by the high levels of glucose in the eye. The lens absorbs this sugar, but cannot use it all for fuel. Instead, glucose and other sugar products accumulate within the lens, drawing in fluid like a sponge. The lens swells, changing its focusing power, causing a change in vision. This fluctuation often continues until the glucose levels are returned to stable, normal levels. Over time, however, the chronic buildup of sugars in the lens can lead to the formation of cataracts, causing blurring of vision which does not improve with glucose reduction. It is not uncommon to see cataracts develop at an earlier than usual age in diabetics.
Blood vessels are particularly sensitive to the effects of elevated glucose. Over time, particularly with poorly controlled disease, diabetes can damage tiny blood vessels known as capillaries, where oxygen is passed from blood to organs. This damage occurs throughout the body, including the kidneys, heart, brain, nerves, and eyes. Within the eye, the structure most sensitive to these changes is the retina. The retina is the thin, light-sensitive membrane which lines the inside of the eye. Like the film of a camera, it forms the image we see from light focused upon it by the cornea and lens. With a very intricate network of fine blood vessels and capillaries, the retina is very sensitive to injury from chronically elevated blood sugar. This injury, known as diabetic retinopathy, occurs in stages. A normal, healthy retina is seen to the right. The yellow optic nerve is seen with retinal blood vessels branching from it.
The earliest retinal changes do not cause any visual symptoms, however are visible to your doctor during an examination of your eye. For this reason, regular exams are important. Small dilations of the capillaries, known as microaneurisms, are common. As damage progresses, the capillaries become leaky, and the components of blood begin to accumulate within the tissue of the retina. Small spots of blood develop. Fluid collects, forming patches of edema, or swelling, in the retina. Fats and proteins also leak out, seen as yellow-white deposits known as exudates. Together, these hemorrhages, exudates, and edema, known as non-proliferative diabetic retinopathy, can blur the vision. If not treated, visual loss can become permanent. Hemorrhages and exudates are pictured at left.
As damage to blood vessels progresses, oxygen can no longer be effectively passed to the retinal cells. Cells begin to starve, and eventually die, causing further, permanent loss of vision. This stage of disease, which most well controlled diabetics will fortunately not reach, is the turning point to what is known as proliferative retinopathy. As retinal cells starve for oxygen, they begin to release chemical signals which stimulate the growth of new blood vessels, a process called neovascularization. Unfortunately, these vessels- the body’s attempt to reestablish the vital flow of blood- grow in an uncontrolled, haphazard manner and fail to perform their intended service. Instead, they proliferate not only on the retina, but also into the vitreous, as well as on more anterior structures such as the iris and drainage angle of the eye. These vessels are very delicate and prone to rupture, causing hemorrhaging of the retina and vitreous.
A new vitreous hemorrhage is often heralded by sudden loss of vision, often with an initial red tinge. Vessels grow with a scaffolding of fibrous tissue which has contractile properties. With time, contraction of these fibrovascular membranes can lead to traction detachments of the retina, where the retina is literally pulled off of the eye, causing significant loss of vision. In the front of the eye, fibrovascular tissue causes a secondary closure of the drainage angle, leading to neovascular glaucoma (see section on glaucoma for more information), often with very high, difficult to control intraocular pressures. By this point, visual loss is often severe and permanent. Neovascularization extending from the optic nerve is seen above right, and a vitrous hemorrhage to the left.
While diabetes brings the potential for visual loss, much of this damage can fortunately be prevented or treated. Without doubt, the most important aspect of treatment is good control of blood sugar levels. It is very important to work with an internist, family physician, or endocrinologist to achieve well-controlled, normal glucose levels. Numerous studies have demonstrated the ocular benefits of such control. Despite this, however, some will develop retinopathy and require treatment. Treatment for non-proliferative retinopathy is aimed at preventing or eliminating the blood vessel leakage which leads to lost vision. Traditionally, this has been achieved with laser surgery. In this procedure, a laser, which is simply a highly focused, powerful beam of light, is used to create tiny burns at the sites of leakage. Much like spot welding, this serves to close the leaking vessels, allowing the accumulated fluid to dry up and vision to be restored. The procedure, normally performed in a doctor’s office, is relatively brief and usually completely painless. Laser treatment is more effective at preventing loss of vision than restoring it, however, and the goal is early detection and early treatment, before significant reduction in vision occurs.
In addition to laser, newer techniques for the treatment of non-proliferative retinopathy are evolving. One technique, which involves the injection of steroid medication into the vitreous, has demonstrated efficacy in recent studies. The effect may be transient, however, requiring repeated treatments. Additional medications- oral, topical (eye drops), and injectable- are currently being evaluated for treatment of diabetic retinopathy.
Proliferative retinopathy requires more aggressive treatment. The mainstay of therapy for this stage of disease is laser surgery, known as panretinal photocoagulation, or PRP. In this procedure, a laser is used to treat the peripheral sick retina, eliminating the stimulus causing neovascularization. The peripheral retina, which is responsible for peripheral vision, is sacrificed in order to preserve the much more important central vision. While the loss of peripheral vision may be perceived, this procedure is very effective, preventing the severe complications of proliferative retinopathy. The abnormally growing blood vessels regress, eliminating the risks of vitreous hemorrhage, retinal detachments, and neovascular glaucoma. Like the focal laser treatment for non-proliferative disease, PRP is performed in a doctor’s office. However, local anesthesia is often required and the procedure takes more time, often about 20 to 40 minutes depending on the extent of treatment required. Laser burns after PRP are seen in the photo above right.
Most people with diabetes will not develop severe retinopathy. This is particularly true if blood sugar is well controlled. Some, however, will develop disease that requires treatment in order to prevent permanent loss of vision. Diabetics require regular eye examinations to watch for development of retinopathy. Exams are recommended upon initial diagnosis and annually thereafter. If mild retinopathy is present, more frequent visits may be suggested to monitor for the need for treatment.
Please contact us for more information or to schedule an appointment for a diabetic eye examination.