Insights Into Diabetes and Eye Disease

By Sandra L. Weber, MD, FACP, FACE, Charles J. Woody, OD, PhD and Christopher Woody, BS

Our eyes are complex, with many different parts, each of which can be affected when you have a chronic condition like diabetes mellitus. While most of the effects of diabetes on your eye are not noticeable as they typically don’t cause pain and occur very slowly over time, many people falsely feel secure that their vision is not threatened. So, why is a yearly eye appointment necessary? The answer is simple: the undetectable and slow process of changes in the eyes of persons with diabetes should be checked on a regular basis with a thorough eye exam to identify problems before damage is done.

High blood sugar (glucose) levels can cause significant damage to several different parts of your eyes. It’s not a good idea to wait until you notice any change in your ability to see before you contact an eye doctor. Typically, the changes are not noticeable right away and often not until the damage has significantly progressed. This can put you at great risk of losing your vision.

What happens during an eye exam?

First, your doctor will put a couple of drops in your eyes to allow for a better look into the back of the eye, then the exam begins from the front of your eye to the back (figure 1).

Dry eyes and the 20/20/20 rule

Many people suffer from dry eyes, and this is even more common if you have diabetes. Tears are needed to keep the surface of your eyes (the cornea) moist at all times. Fortunately, there are many things you can do to keep your eyes comfortable, which include eye drops such as artificial tears or prescription eye drops that are lubricant and/or anti-inflammatory in nature. Mild dehydration often makes dry eye problems worse, especially during hot, dry and windy weather. Simply drinking more water helps to reduce the symptoms of dry eye syndrome as does blinking more often.

When using a computer, smartphone or other digital device, studies have shown that we tend to blink less frequently which can cause or worsen dry eye symptoms, so it is best to take frequent breaks while using a computer. A suggested approach is to look away from your screen at least every 20 minutes and look at something that is at least 20 feet from your eyes for at least 20 seconds – the "20-20-20 rule." This approach can help relieve both dry eyes as and computer eye strain.

Studies have shown that supplements containing fish oils (omega-3 fatty acids) can decrease dry eye symptoms. Food sources of omega-3s include cold-water fish such as salmon, sardines, herring and cod. For a vegetarian source of omega3s, some eye doctors recommend flaxseed oil.

Women should remove their eye makeup thoroughly each night. Eyeliner and other eye makeup can clog the openings of glands at the base of the eyelashes and increase dry eye sensation. Avoiding eye makeup or using as little as possible can help. After removing eye makeup, apply a warm, moist washcloth to your closed lids for a minute or two, then gently scrub lids and lashes with a mild cleaner, such as diluted baby shampoo or pre-moistened eyelid wipes sold in drugstores.

It is also recommended that you wear quality sunglasses, specifically a pair that blocks the sun's UV rays. Additionally, if your sunglasses have a wrap-style frame, this can add to the protection from wind, dust and other irritants that can worsen dry eye symptoms. Over time, the cornea tends to become less sensitive to pain as diabetes progresses. This can cause you to blink less, which will make your dry eyes even drier. You can also be more likely to develop eye infections such as pink eye.

Diabetes and Vision Change

One of the key signs of poor glucose control is fluctuation in your vision. Many people recognize this problem when they find that they frequently need new glasses or contact lenses. A good rule of thumb is to make sure your blood sugar levels are stable and maintained, as much as possible, for three weeks before you get a prescription for glasses or contact lenses.

The lens in the front part of your eye focuses light and images onto the back of your eye, the retina (figure 2). Most people with diabetes recognize that their vision changes when their glucose levels change. This is because the amount of fluid inside the lens increases as your blood glucose levels rise. The higher your glucose, the more fluid inside the lens and the more change in where the lens focuses light. Your ability to focus varies if your blood glucose changes often.

Cataracts occur when there are changes to the lens that interfere with letting light through the lens. The lens becomes less clear and develops a light brown tint (figure 3) The higher your blood glucose, the more rapidly the lens inside your eye can deteriorate, leading to annoying fluctuations in your vision and an increase in the rate at which you develop cataracts. Eventually, the lens will become so damaged that you will not be able to see well enough to read, drive a car, or even watch television. When the cataract gets to this point, the only treatment is surgery to remove the lens and replace it with an artificial lens. Before you have any surgery, however, it is very important that you have your diabetes under control.

Get ahead of glaucoma

Glaucoma is a condition in which the pressure inside your eye is increased, leading to damage to the nerve that sends the signal of what your eye sees to the brain to be processed into an actual image. Untreated, glaucoma can ultimately lead to blindness. Part of your routine eye exam is to check your eye pressures for signs of glaucoma, as you are at increased risk for developing glaucoma if you have diabetes. Patterns over time can be identified and treatment started before there is nerve damage.

There are several different types of glaucoma. With “open-angle” glaucoma, there are no warning signs or obvious symptoms in the early stages, another reason why a routine eye exam is so important, especially if you have diabetes. As glaucoma progresses, blind spots can develop in peripheral (side) vision, but most people with open-angle glaucoma do not notice any change in vision until the damage is quite severe.

Diabetes can also cause damage to the nerves controlling the movement of your eyes, which can cause very rapid, and frightening, changes in vision. It can lead to double vision, drooping of the eyelid and the eye pointing in a different direction than usual. These are called cranial nerve palsies. If you notice these changes, see your eye doctor as soon as possible.

Diabetic retinopathy and macular edema

One of the most well-recognized complications of diabetes is the development of what is known as diabetic retinopathy (figure 4). This is bleeding inside your eye which often occurs when high blood glucose levels lead to decreased blood supply to the tissue in the back of the eye, leading to loss of this tissue. In turn, the eye tries to repair itself, triggering the formation of new, but very fragile, blood vessels, which can leak fluid or bleed. This condition may cause significant loss of vision, sometimes permanently.

Diabetic retinopathy is often present for years without having any effect on your vision until sometimes it’s too late. It is important for your doctor to dilate your eyes to examine these blood vessels closely and to look for any leakage. This is the only place in your body a doctor can see your blood vessels and gives your doctor a good idea of how diabetes is affecting the other blood vessels in your body.

Finally, there is a condition called macular edema, which is a buildup of fluid in the macula, the small area at the center of the retina responsible for what we see at the center of our field of vision. This fluid buildup causes the macula to swell and thicken, which distorts vision (specifically straight-ahead vision), color vision and sharpness of vision.

Treatment for macular edema has evolved from laser photocoagulation, a procedure in which the heat from a laser is used to seal or destroy abnormal blood vessels in the retina, to drug treatments injected directly into the vitreous gel, the fluid in the center of the eye. These injections, known as intravitreal injections, are usually performed by a retina specialist, an ophthalmologist with extra training in diseases of the retina.

All the parts of your eye need to be healthy to protect your vision, which is why regular eye exams are crucial. With regular checkups, you can keep minor problems minor. And if you do develop a major problem, there are treatments that often work well if you begin them right away.

“Angle-closure” glaucoma is also typically silent before it strikes. Some early symptoms of an attack may include blurred vision, halos, mild headaches, or eye pain. People with these symptoms should be checked by their eye doctor as soon as possible.