“…the eyes are the windows of the soul.”
— Max Beerbohm
Much of the effort you put into your daily diabetes care is aimed at preventing the chronic or long-term complications that can occur with diabetes. Over time, less than optimally controlled blood glucose and blood pressure levels can cause damage to blood vessels, nerves, and organs in the body, including the eyes.
There are several diabetes-related complications that affect the eyes; the most common is retinopathy. Every year, retinopathy results in blindness for over 10,000 people with diabetes, and many more experience partial vision loss. In addition to retinopathy, cataracts may occur at a younger age in people with diabetes, and a person with diabetes is twice as likely as the general population to develop glaucoma.
The positive message regarding eye diseases that are related to diabetes is that many are preventable by keeping blood glucose levels and blood pressure levels well controlled. Regular visits with an eye specialist are also key to keeping your eyes healthy and catching problems early, when they’re most treatable.
How the eye works
For such a small organ, the eye is both fascinating and complex. Your eyes make constant adjustments to allow you to see objects that are nearby as well as those that are far away at all different levels of light. And they do it instantaneously.
The outermost layer of the eyeball is a tough, white layer called the sclera, which has a transparent window in front called the cornea, through which light enters the eye. Just behind the cornea are the iris, the colored part of the eye, and the pupil, the black opening in the center of the iris. The iris controls the amount of light that enters the eye. When it is dark, the muscles in the iris contract, allowing the pupil to dilate and let in more light, and when it is bright, the muscles of the iris cause the pupil to constrict, letting in less light.
Behind the iris is the lens, a flexible structure that focuses light on the retina, the innermost layer of the eyeball. The retina contains millions of cells called rods and cones, which respond to light. A small area in the retina called the macula contains only cones and is the area of sharpest vision. Signals from the rods and cones travel via the optic nerve to the brain, and the result is vision.
The lens divides the eyeball into two fluid-filled chambers, the anterior (front) chamber, and the posterior (back) chamber. The anterior chamber contains a watery fluid called aqueous humor, and the posterior chamber contains a gel-like substance called vitreous humor. Both substances help the eyeball maintain its shape, and the aqueous humor additionally provides nutrients for the lens and cornea, which do not have a blood supply.
The eye is connected to a number of muscles, nerves, and blood vessels that work together to maintain its function. The structures around the eye, such as the eyelids, eyelashes, and tear ducts, help protect the eyes from wind, dust, germs, and other substances. A delicate membrane called the conjunctiva lines the eyelids and covers part of the outer surface of the eyeball. The conjunctiva secretes mucus, which helps to keep the eyeball moist. (See “Anatomy of the Eye” for an image of the various structures of the eye.)
Diabetes-related eye diseases include a group of disorders that can cause partial or total loss of vision; among them are diabetic retinopathy, cataracts, and glaucoma. All are typically associated with periods of high blood glucose levels as well as with high blood pressure.
Retinopathy. The term “retinopathy” means “disease of the retina,” and the type of retinopathy that is associated with diabetes is often referred to as “diabetic retinopathy.” Both high blood glucose levels and having had diabetes for a long time raise the risk of developing diabetic retinopathy. In retinopathy, the blood vessels in the retina are damaged. Two types of changes in the retinal blood vessels can occur as complications of diabetes: nonproliferative retinopathy (also called background retinopathy), and proliferative retinopathy.
In nonproliferative retinopathy, small blood vessels in the retina swell, weaken, and leak blood and fluid into the posterior chamber of the eye. The retinal tissues become swollen, and when the area of the retina called the macula is affected (a condition called macular edema), the result is blurry vision and sometimes changes in color perception. However, in its early stages, nonproliferative retinopathy may cause no symptoms at all.
In proliferative retinopathy, fragile, new blood vessels form and grow over the retina. The new blood vessels often leak blood into the vitreous humor, causing cloudy vision. The formation of new blood vessels can also lead to scarring, which can pull on the retina, leading to retinal detachment and loss of vision. If a detached retina is treated early, vision often returns to normal, but in advanced cases, vision loss can be permanent.
Both nonproliferative and proliferative retinopathy can be treated with laser photocoagulation, in which laser beams are used to seal leaky blood vessels and destroy abnormal new blood vessels. If a large amount of bleeding has occurred as a result of retinopathy, a vitrectomy, in which the vitreous humor is removed and replaced with a saline solution or other substance, may also be performed.
Cataracts. A cataract is a clouding of the lens in the eye. While many people will develop cataracts if they live long enough, those with diabetes tend to develop cataracts at an earlier age. In fact, having diabetes is considered a risk factor for the development of cataracts. Symptoms of cataracts include the following:
- Cloudy or blurry vision
- Changes in color vision (colors may appear faded or yellowish)
- Increased sensitivity to light (lights appear too bright)
- A glare or halo effect around lights
- Poor vision, especially at night
- Double vision or multiple images in one eye, which may actually get better as the cataract gets larger
- Frequent changes in eyeglass or contact lens prescriptions
The treatment for cataracts is surgical removal of the cloudy lens and, generally, replacement with an artificial lens. According to the National Eye Institute, cataract surgery results in improved vision in 90% of cases. When to have surgery is typically decided by the person who has the cataract and the physician treating the eyes. Surgery usually is scheduled when vision becomes impaired enough to interfere with activities of daily living or to pose a threat to personal safety or when discomfort occurs. A cataract may also be removed if it interferes with examination or treatment of another eye problem. Before surgery, some people with cataracts benefit from adding or changing prescription eyewear, using sunglasses to diminish bright light, and/or adjusting the lighting in their homes and work environments.
Glaucoma. The most common type of glaucoma in people with diabetes is called open-angle glaucoma, and it occurs when the fluid pressure inside the eyes rises, resulting in damage to the optic nerve. It can ultimately cause loss of vision. Glaucoma has no symptoms in its early stages. As the disease progresses, a person’s peripheral (side) vision may decrease. If the glaucoma continues without treatment, tunnel vision can occur, with an eventual loss of sight.
With early treatment, serious vision loss from glaucoma can often be prevented. Prescription medicines that cause the eye to make less fluid or that help fluid drain from the eye can help lower eye pressure. A procedure called laser trabeculoplasty can also help fluid drain out of the eye. This procedure can typically be done in a physician’s office and is usually very effective in reducing eye pressure. However, the use of prescription medicines for glaucoma usually must be continued after laser trabeculoplasty.
If neither medicines nor laser trabeculoplasty control your eye pressure, conventional surgery to create a new opening for fluid to leave the eye may be recommended. This surgery may be done in an eye clinic or hospital, and it is more likely to be successful if you haven’t had any previous eye surgery.
Your plan of defense
Your first best defense against diabetes-related eye problems is maintaining optimal blood glucose control. Research has shown that doing so can substantially reduce both the risk of developing diabetic retinopathy and its progression, should it occur. (See “Blood Glucose Targets.”) Your other best defense is to keep your blood pressure at the recommended level as well. (See “Optimal Blood Pressure.”) If you smoke, quitting smoking will help to prevent cataracts as well as most of the major complications associated with diabetes. Smoking also raises the risk of developing age-related macular degeneration, a disease that destroys sharp, central vision and is the major cause of vision loss in Americans over age 60.
The presence of nephropathy (kidney disease related to diabetes) raises the risk for retinopathy, and in women with Type 1 diabetes, pregnancy may raise the risk. Pregnancy can also cause a rapid increase in the progression of retinopathy in women who already have diabetic retinopathy before becoming pregnant. It has been theorized that this progression may be caused by a rapid improvement in blood glucose control during early pregnancy.
According to the American Diabetes Association, adults and adolescents with Type 1 diabetes should have a comprehensive dilated eye examination by an ophthalmologist or optometrist within three to five years of the onset of diabetes. Those with Type 2 diabetes should have an initial dilated eye examination by an ophthalmologist or optometrist shortly after being diagnosed with diabetes. After your initial eye examination, you should meet with the eye specialist once yearly. The only exceptions might be if you have eye problems that require more frequent visits, if you are planning a pregnancy, or if you are pregnant and your eye specialist deems that more frequent exams are needed. Also, if you have a normal eye exam, your eye specialist may recommend less frequent examinations.
The eye specialist (ophthalmologist or optometrist) that you see should be knowledgeable about and experienced in treating diabetes eye disorders. During your eye examination, a visual acuity test will likely be done to measure how well you see at various distances. After drops are placed in your eyes to numb them, a tonometer will be used to measure the pressure inside the eye to check for glaucoma. It is likely that a visual field test to measure your peripheral (side) vision will be performed. Additional drops will be placed in your eyes to dilate, or widen, your pupils. Your eye specialist uses a special lens to magnify and examine your retina and optic nerve for signs of damage. He may take photographs of your eyes to compare to any previous photographs (or any future photographs) to see if any changes have occurred.
Each eye examination is an opportunity to see if any changes have taken place in your eyes since the previous examination. If changes have occurred, prompt treatment can often prevent further damage. Research confirms that visual loss can be avoided if problems are detected and treated early. The risk of severe visual loss is reduced by at least 50% if laser photocoagulation is done in the earlier stages of retinopathy.
After a dilated eye exam, your close vision may remain blurred until the dilation wears off, and your eyes may be sensitive to light. It’s a good idea to bring a pair of sunglasses to wear afterward and to arrange for someone to pick you up at the doctor’s office so you won’t have to drive.
Don’t wait for symptoms of eye disease to occur to make an appointment with an eye specialist. Many times, there are no symptoms until an eye problem is severe. If you don’t currently have an ophthalmologist or optometrist who specializes in diabetes-related eye disease, the time to find one is now. (For suggestions on doing so, see “Finding an Eye Care Specialist.”) If you do have an eye specialist, keep your visits current. After all, your vision is precious and worth keeping if you can.