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Diabetes: An Overview
Introduction
Diabetes has become a major health issue in North America, with more than three million people in Canada having been diagnosed. More than half of these patients are of working age, between the ages of 25 and 64 years of age. In the US, according to the National Diabetes Statistics Report of 2014, diabetes affects 21 million people. It is estimated that almost 30% of diabetic patients are still undiagnosed. The burden on health care in both countries is becoming heavier each year.
The impact of diabetes on eye health is immense; diabetes is one of the leading causes of blindness in North America.
The incidence of diabetes is still increasing at an alarming rate, which most experts blame on the apparent epidemic of obesity in today’s modern societies. However, one factor may be that methods of diagnosis have improved, which makes it easier to identify those who might have gone undiagnosed in the past.
What is Diabetes?
Diabetes is a disease that causes the blood glucose levels to be too high. After a meal, food is broken down in the digestive system and converted into glucose, a form of sugar. Normally, glucose is transported by the circulatory system from the blood to individual cells in the body. Insulin, which comes from the organ called the pancreas, is needed to convert the glucose into energy.
In Type 1 Diabetes (T1D), also known as juvenile- or early-onset diabetes, there is an insufficient amount of insulin produced.
In Type 2 Diabetes (T2D), also called late-onset or adult-onset diabetes, the pancreas produces enough insulin, but the body does not use it properly.
A prolonged increase in the level of blood sugar can lead to nerve and blood vessel damage, which can cause damage to the circulatory system itself, and result in stroke, heart disease, damage to the extremities (which can require eventual amputation), blindness and even death.
The Effect on the Eyes
As we have seen above, diabetes is a disease that profoundly effects the circulation throughout the entire body; what happens in the entire body obviously happens within the eyes as well.
The retina, the layer of nerve fibers that transmit visual signals to the brain via the optic nerve, must get its nutritional needs from two main sources, one of which is the retinal artery and its branches, superior and inferior. These arteries carry oxygen and nutrients to the retinal nerve fibers. The corresponding retinal veins carry de-oxygenated blood and waste products back out of the eye to the heart and lungs. The second source of oxygen to the retina is the choroidal blood vessels, which line the inside of the eye just behind the retina, where oxygen and nutrients are diffused into the retina.
(Figure 1: The normal retina, showing optic nerve head left of center and normal retinal arteries and veins arcing around the normal macula, dark spot at right center.)
The most damaging eye condition caused by diabetes is that of diabetic retinopathy, which causes the circulation to be so compromised that hormones called vessel growth factors (VGFs) signal the arterial and venous branches to grow new vessels to bypass the damaged ones. This might sound like a good thing, but actually the new vessels are so fragile that even a coughing spell can cause them to rupture and bleed into the back of the eye. If this continues, the blood will not only block the transmission of light but will cause permanent damage and scarring of the retinal tissue.
(Figure 2: An eye with moderately severe proliferative retinopathy. Notice the significant bleeding and white deposits, along with the general congested appearance.)
Diabetic retinopathy is usually classified as being background, pre-proliferative or proliferative retinopathy. The first stages, background retinopathy, are early changes to the blood vessels and deposits that form on and in the retina; this stage does not usually cause noticeable vision loss, but signifies that changes are beginning to occur. In the pre-proliferative stages, there is evidence of more severe changes, perhaps with tiny “dot-blot” hemorrhages visible. Vision may be somewhat affected at this stage.
Proliferative diabetic retinopathy is when there are new vessels growing in the back of the eye, forming web-like structures of new and fragile growth. Vision is usually at least moderately affected in the early stages of proliferative retinopathy, but as time passes, profound vision loss may occur.
In severe diabetes, the blood sugar can increase or decrease rapidly, and this can cause what is known as a diabetic cataract. A cataract is a cloudiness found in the crystalline lens of the eye, which can interfere with vision. A diabetic cataract is a special type of cataract where the lens isn't so much cloudy as it is changed by the blood sugar; the usual change is to increase myopia (nearsightedness) or to decrease hyperopia (farsightedness). The result is blurry vision which can usually be treated by changing the eyewear lens prescription, but because these cataracts are transient and usually resolve when the blood sugar is normalized getting new lenses isn’t indicated. This type of cataract, also known as a myopic shift, is more of a diagnostic clue rather than a call for a new lens prescription.
People with diabetes are also 40% more likely to develop glaucoma, a condition characterized by increased pressure within the eye, which can damage the optic nerve.
Treatment
Laser surgery can be a tool useful to an eye surgeon to seal off the new blood vessels before they begin to leak fluid and blood into the eye. It is important that this be done early on, because later in the process of progressive changes it is much more difficult to interrupt the process. Even so, vision does not always return to normal.
(Figure 3: A right eye showing circular scars from laser treatment of proliferative diabetic retinopathy.)
Another method of treatment is to inject medications called anti-VGFs into the eye to stem the growth of new circulatory nets. There are several different anti-VGF medications being used presently.
In some cases, steroids can be injected into the eye as well, to suppress the inflammatory response and stabilize progression.
For more information about diabetic retinopathy and its treatment, please see our article titled Effects of Diabetic Retinopathy and Treatment Options.
Importance of Early Detection
Very often, people with diabetes do not know that they have retinopathy until their vision changes significantly; there is no pain or any other symptoms that would give warning until the retina has already been damaged.
For this reason, people who are diabetic are urged to have a diabetic retinal examination at least once a year, even if their diabetes is well-controlled. If the diabetes is not controlled, or if changes are noted, your eyecare practitioner may recommend more frequent checkups.
Summary
Prevention of diabetic retinopathy is best prevented by doing everything possible to keep the diabetes well controlled. Maintaining normal blood glucose levels, blood pressure and blood lipids, and eating a healthy diet is important, as is losing weight if necessary, to reduce the stress on the body in general.
It is important, however, for family members and caregivers to understand that diabetes and its complications can be quite difficult or even impossible to overcome, and that even the best efforts and intentions do not always result in complete control of this disease.
If you are diabetic, eat well, get exercise, take medication if necessary, and do everything possible to keep blood sugar levels as close to normal as possible. As we make more progress in healthcare research, there is always hope for better and more effective treatment strategies, and perhaps eventually, to find a way to cure this devastating disease.
