EYE DISORDERS 

DIABETES

Diabetic Eye Disease

Diabetes mellitus is the leading cause of new cases of legal blindness in working age Americans. It is estimated that 14 million Americans have diabetes, but that only one half of these are aware of it. This page discusses ocular complications of diabetes, and their treatment.

RETINAL COMPLICATIONS OF DIABETES

Diabetes Mellitus is more than just a problem with the control of the blood sugar. It is a vascular disease: a disease of the blood vessels. Diabetes can lead to complications throughout the body, including blood vessel problems in the kidneys, heart, brain, and eyes. The retina lines the inside surface of the eye and receives and processes visual information for their transmission to the brain via the optic nerve. The primary source of blood supply to the retina comes from a single artery, the central retinal artery, which enters the eye through the optic nerve. Once inside the eye, the artery branches on the surface of the retina into smaller and smaller vessels to supply all of the retina.

An especially critical part of the retina is the "macula" which serves the central vision of the eye, or the reading vision. There is a pin-point spot of the macula called the "fovea" which has the sharpest vision.

The eye is unique in that living blood vessels in the retina can be observed by the examining physician. A number of problems can arise in the retina as complications of diabetes. Risk factors for the development of these complications include:

• The severity of the diabetes (being insulin or not insulin dependent to control the blood sugar).
• The control of the diabetes (it has been found that very tight control of the blood sugar can reduce the risk of retinal complications).
• The presence of other medical problems such as increased blood pressure or cholesterol.
• The duration of having diabetes.

It has been found that the longer one has diabetes, that there is more risk for developing retinal complications:

• After 5 years, 25% of insulin-dependent diabetics have some retinopathy.
• After 10 years, 60% have retinopathy.
• After 15 years of insulin-dependent diabetes, 80% have retinopathy, with 25% having the more severe "proliferative diabetic retinopathy".

Diabetic Retinopathy

Background Diabetic Retinopathy

The earliest or mildest diabetic effect on the retina is called "background diabetic retinopathy". This condition can occur in one or both eyes in people with diabetes. When the ophthalmologist examines the retina (usually after dilation), small haemorrhages can be seen scattered within the retina. Irregularity of blood vessels, and mild blockage of blood vessels also can occur. Small dilated blood vessels called "microaneurysms" commonly occur, and appear as tiny red dots in the retina. Clear fluid can leak from these microaneurysms and from abnormal damaged blood vessels into the retina. When this occurs, the retina will swell in thickness like a sponge, and white deposits, or exudates, can form. This swelling can damage the vision, if present for a long enough time. Background diabetic retinopathy can occur in people who are not even aware that they have diabetes. An ophthalmologist observing such incidental findings during a retinal examination might suggest an evaluation to look for diabetes being present.

Background diabetic retinopathy itself does not usually damage the vision, but it does indicate that diabetes is affecting the vascular system of the eye and probably of the entire body. People with background diabetic retinopathy are usually re-examined in at least 6 months.

Diabetic Macular Edema

A complication of background diabetic retinopathy, and also of more severe forms of diabetic retinopathy, is diabetic macular oedema. Oedema is swelling of the retina. The macula, as discussed above, is responsible for the sharpest, central vision that a person has. In diabetic macular oedema, clear fluid leaking from damaged blood vessels in the retina and from microaneurysms causes the retina to swell and thicken. When this occurs in the macula, the reading or central vision is at risk, and can be lost. Extensive studies have been undertaken to determine when diabetic macular edema should be treated, and when it can just be monitored. Sometimes an additional test called a "fluorescein angiogram" can be done to help to determine the source and extent of fluid leakage.

Diabetic Retinopathy NPDR

Proliferative Diabetic Retinopathy

A more severe retinal complication of diabetic eye disease is "proliferative diabetic retinopathy". Fortunately, only a small number of diabetics will develop this complication, but it is still treatable. Here, the vascular damage to the retina worsens, with more extensive haemorrhages, abnormal blood vessels, areas of blocked off blood vessels, and fluid leakage into the retina. The closure of small retinal blood vessels can become so severe that parts of the retina begin to produce a chemical (recently identified) that stimulates the growth of NEW blood vessels. This chemical spreads into the jelly-like material that fills the eye, and can affect many different parts of the eye.

The new blood vessels which form in response to this chemical are abnormal, frail, and tend to grow out off of the retinal surface into the jelly material filling the eye. They tend to break and bleed, causing large haemorrhages inside of the eye, and can become scarred, leading to retinal detachments. In a detachment, the retinal is tented off of the wall of the eye, being pulled up by these abnormal blood vessels.

This complication of diabetes requires more extensive treatment, and sometimes intra-ocular sugery done in the operating room. Sometimes blood vessels can block off supplying the central vision itself. If this occurs, the central vision is lost and cannot be regained.

Diabetic Retinopathy PDR

Evaluation and Treatment of Diabetic Eye Disease

The diagnosis of diabetic eye disease requires dilated retinal eye examinations at periodic intervals. If there is no retinal complications of diabetes, an annual examination is suggested. If there are retinal changes present, follow-up examinations ranging from 1 to 6 months may be necessary. In cases of more severe retinal complications, an additional test if often done:

Flourescein Angiogram

A fluorescein angiogram is a test done in the office where a pigmented dye is photographed as it passes through the retinal blood vessels. For this test, the eyes are dilated, and initial color photographs are taken of the retina by the photographer. Then, the fluoresein dye is injected into an arm vein by a physician. This is similar to having blood drawn. Once the dye is in, the needle is removed, and the photographs are taken. The dye reaches the eye in a matter of seconds. About 30 photographs are taken between the two eyes over a 10 minute time span. The film is then developed, and the ophthalmologist studies the results. Important information about the leakage and blockage of blood vessels can be gained from this test, as well as the presence of abnormal blood vessels.

Treatment of diabetic retinal disease

Many diabetic retinal problems are treated using a laser. The laser casts a tiny spot of light onto the retina in order to seal leaking blood vessels or to prevent the formation of abnormal blood vessels. Laser treatment is done as an outpatient operation, but usually only eye drop anaesthesia is needed. The patient is seated at the laser, and treatments usually range from 5 to 20 minutes. Sometimes, repeat treatments need to be done.

• For diabetic macular oedema, the laser is used to seal leaking blood vessels which are causing the retina to swell dangerously. This procedure is called "focal" or "grid photocoagulation". Studies have identified precise situations when this condition should be treated. The vision does not need to be reduced before treatment is done, since the goal of the surgery is to maintain the vision at least at where it is.
• For proliferative diabetic retinal disease, the source of the chemical causing abnormal blood vessels to grow within the eye must be eliminated. The laser is used to diffusely treat retinal areas which have lost their blood supply to allow the abnormal blood vessels to stop growing and shrink down. Sometimes this laser surgery is broken up into several "sittings".

In cases where extensive bleeding has occurred inside of the eye, or if retinal detachments have formed, intra-ocular microsurgery is needed to correct the problem. This is termed a "vitrectomy", and is usually performed by a retinal specialist in the operating room.

Other Complications of Diabetes

Fluctuations of Vision

If the blood sugar in diabetes becomes elevated to a very high level (usually over 300) the natural lens inside of the eye can become affected. The high levels of sugar leach into the lens, and cause it to begin to swell with fluid. This can cause a shift in a glasses prescription, often toward farsightedness. Vision can become progressively blurrier for both reading and distance vision, and usually both eyes are affected. After the blood sugar is brought under control, the lens may remain swollen for weeks! It may take up to 6 weeks for the glasses prescription to return to normal in some cases. A person may have to go through several temporary pairs of glasses in order to function during this transition.

Cataract

Diabetes is a risk factor for developing cataract, which is a clouding of the lens within the eye. If this occurs, the vision may become permanently blurred and not improvable with a change in glasses. Sometimes, cataracts associated with diabetes can be more rapid to develop and can have more severe glare symptoms. Cataract extraction can cure the problem, but there is some risk of a flare up of diabetic retinal disease immediately after surgery. The reason for this is not well understood. Sometimes, cataract can be so severe that the retina cannot even be examined by the ophthalmologist, and the cataract may have to be removed just to be able to see or treat the retina.

Glaucoma

Diabetes may increase the risk of glaucoma, a disease where usually increased pressure in the eye damages the optic nerve carrying visual signals from the eye. A more severe form of glaucoma can occur also, called "neovascular glaucoma". Here, abnormal blood vessels begin to grow on the iris near the front of the eye. This can occur with proliferative diabetic retinopathy. If laser surgery is not done to force regression of the blood vessels, they can continue to grow and can rapidly damage the outflow channels of the eye. Once these channels are scarred closed, the pressure in the eye can skyrocket in a form of glaucoma that is very difficult to treat.

Prevention of Diabetic Complications

Early detection of diabetic eye complications is the key to successful treatment. The patient with diabetes should watch out for any changes in vision, and keep regular appointments with an ophthalmologist knowledgeable in the diagnosis and treatment of diabetic eye disease.

• A person recently diagnosed with diabetes should have a complete eye examination.
• If the retina is free of any diabetic complications, the eye exam should be repeated annually.
• If there is a blurring of vision, this may indicate that the blood sugar is elevated. If the blurred vision continues, or if floaters or other symptoms are experienced, the eyes should be re-examined.
• With active diabetic retinopathy, even if mild, the eyes should be examined at 1 to 6 month intervals.