DIABETES AND THE EYE

by David Harper, MD

As a diabetic, you will be aware of the changes that occur in the body of a person who has diabetes, as well as the specific tasks you must perform to properly control this disease. Even though we know the importance of these activities, we often take for granted the importance of sight.

A sight-threatening condition known as diabetic retinopathy affects a high percentage of diabetics annually. It is a disease that, if detected early enough, can be treated, and blindness may be prevented.

The Normal Eye

Our eye works very much the same way as a camera. When you take a picture, the lens of the camera focuses light through the front of the camera onto the film that is loaded along the back wall of the camera. Once the light hits the film, a picture is taken.

With regards to the human eye, light passes through the cornea, the clear outer layer of the eye. This light is focused by the cornea and the lens onto a thin layer of tissue located in the back of the eye called the retina. Once the light hits the retina, a picture is taken. This picture is transmitted to the brain through the optic nerve and transformed into what we see.

Diabetic Retinopathy

Diabetic retinopathy can be simply defined as changes in the blood vessels of the eye resulting from diabetes. The retina is filled with a series of tiny blood vessels that supply the oxygen necessary to maintain a healthy retina. Diabetes causes blood chemistry changes, such as high blood glucose levels that can damage these tiny blood vessels, reducing the supply of oxygen to the retina.

There are two stages of diabetic retinopathy; Non-proliferative Diabetic Retinopathy (NPDR, often called background retinopathy), and Proliferative Diabetic Retinopathy (PDR).

NPDR is the early stage of diabetic retinopathy. In this stage, the original blood vessels, once damaged, begin to leak fluid or blood into the retina. This small amount of blood or fluid may not affect your vision immediately—however, if left untreated, it could cause vision problems.

PDR is a more severe form of diabetic retinopathy. To compensate for the reduction in oxygen supply resulting from the damaged vessels, the retina may begin to grow new blood vessels. This process is known as neovascularization. These new blood vessels are weak and may eventually break, leaking a significant amount of blood into the vitreous, the clear gel that fills the back portion of the eye between the lens and the retina. This leakage of blood into the vitreous is commonly referred to as a "vitreous hemorrhage," and it typically compromises a person's vision.

Treatment of Diabetic Retinopathy

Research has shown that you can reduce the risk of developing diabetic retinopathy by controlling your blood sugar level. For those who have developed diabetic retinopathy, early treatment is very important. Diabetic retinopathy can be treated by laser surgery that uses a tiny laser beam to close off areas of the damaged retina, in order to stop the bleeding or development of abnormal blood vessels. This is performed in your ophthalmologist's office on an outpatient basis.

If significant bleeding has occurred and a vitreous hemorrhage exists, your doctor may not be able to view the retina, thereby restricting his/her ability to treat it with a laser. At the same time, your vision would be obstructed. Two options are available to you when this happens. You can wait for a period of time to see if the hemorrhage clears on its own (commonly called "watchful waiting"), or you can undergo a surgical procedure called a vitrectomy where the blood clouded vitreous is removed from the eye. Once this vitreous is removed, and replaced with a clear substance, the retina can be treated with a laser as described above.

Future Treatment Options on the Horizon

Many treatment options are currently being explored for the prevention and treatment of diabetic retinopathy and of conditions caused by diabetic retinopathy. Advanced Corneal Systems, Inc., of Irvine, California, is currently evaluating the use of an investigational drug, Vitrase™ (hyaluronidase) for ophthalmic intravitreal injection. A Phase III clinical investigational trial is currently underway in the U.S., to determine its safety and effectiveness in the clearance of vitreous hemorrhage. This investigational drug could potentially decrease the time that diabetics would have to wait for a hemorrhage to clear, and/or decrease the need for a vitrectomy procedure. Early studies have shown the drug to be well tolerated by most patients.

While this investigational drug looks promising, the best treatment is always prevention. People with diabetes should work with their health care provider to achieve good blood glucose and blood pressure control and have regular eye examinations in order to detect diabetic retinopathy at an early stage and initiate early treatment.