HELP ON DIABETES

DIABETIC EYE DISEASE

Diabetic eye disease includes three conditions: diabetic retinopathy, cataracts, and glaucoma.

Diabetic Retinopathy

At the back of the eye on the retina are tiny blood vessels that nourish the nerves of the eye. High glucose levels or high blood pressure can injure the cells lining these blood vessels (retinopathy). The earliest visible abnormalities are pinhead red dots next to the blood vessels that may come and go—these are called microaneurysms or dot hemorrhages. Further injury then causes leakage of blood and fluid into the surrounding areas. The hemorrhages have a characteristic appearance—they are known as blot and flame hemorrhages. The fluid leakage causes yellow deposits called hard exudates. These changes in the back of the eye (also called background retinopathy) do not cause any problems with the vision and the patient is unaware of them. They are, however, of concern because if action is not taken to improve the glucose control and lower the blood pressure, they may progress to more serious injury and vision loss.

If there is progression, the injured blood vessels get blocked and the areas of the retina supplied by these vessels become starved of nutrients. The retina responds by releasing chemicals, such as vascular endothelium growth factor (VEGF), that pro­mote the growth of new blood vessels. This abnormality is called proliferative reti­nopathy. Unfortunately, these new blood vessels are fragile and can bleed easily. The hemorrhages from these new vessels can cause sudden loss of vision. The hemor­rhages and growth factors can also cause scar tissue to develop at the back of the eye. This scar tissue can pull on the retina, causing a retinal detachment and vision loss.

The injured blood vessels can also leak fluid and cause swelling in an area of the retina called the macula—this condition, called macular edema, can cause the loss of central vision, making it difficult to read or drive.

One way of protecting vision is to use lasers to destroy the parts of the retina that do not have adequate nutrition so that the new blood vessels that are prone to bleed­ing do not grow. Laser therapy is also used to treat macular edema by removing the areas with very leaky blood vessels. The disadvantage of laser therapy is that it does destroy part of the retina. People who have had extensive laser therapy frequently complain of difficulty with night vision.

Recently, it has been shown that injecting the anticancer drug bevacizumab (Avastin) into the eye can stop the growth of the new blood vessels due to diabetic eye disease. Bevacizumab works by blocking the action of VEGF. 

Cataracts

A cataract is a clouding of the lens of the eye so that the person cannot see clearly. The symptoms of cataracts are

• Gradual blurring of the vision

• Glare in bright light or sunlight

• Poor color vision with fading or yellowing of colors

• Double or multiple images when one eye is closed

 Cataracts occur as part of the natural aging process, but they occur earlier and more often in people with diabetes. It is thought that the high glucose level causes changes in the proteins inside the cells of the lens, altering the optical properties of the lens. The treatment for cataracts is surgery—the cloudy lens is removed and replaced with an artifi cial lens.

Glaucoma

The inside of the eye is fi lled with fluid. New fluid is constantly being made, and the fl uid that is being replaced leaves the eye by entering a drainage meshwork toward the front of the eye. Blockage of the drainage system can lead to increased fl uid pressure within the eye—a condition called glaucoma. This pressure increase can damage the nerves going from the back of the eye to the brain and cause vision loss. Like cataracts, glaucoma occurs more frequently in people with diabetes.

Glaucoma is treated with eyedrops:

• Beta-blocker eyedrops such as timolol (Timoptic), levobunolol (Betagan), and betaxolol (Betoptic) reduce the amount of fluid made. They are usually quite safe, but they can cause breathing problems in patients with asthma or chronic bronchitis. 
• Miotic eyedrops such as pilocarpine (Isopto Carpine) and carbachol (Isopto Carbachol) contract the iris, opening the drainage channels for the fluid to drain. These drops make the pupil smaller, and initially patients may complain of headache and eyestrain, but both usually get better with time. 
• Carbonic anhydrase inhibitors such as dorzolamide (Trusopt) also reduce the amount of fluid made. Sometimes people complain of nausea when they use this type of eyedrop.    

If the drops do not work, an eye operation to allow the fluid to drain (trabeculec­tomy) is performed.

Rarely, glaucoma can occur in people with diabetes when there is blood vessel growth in the iris blocking the fluid drainage channels (a condition called iridis rubeosis). This type of glaucoma is usually treated with lasers. It has recently been reported that bevacizumab might also be effective.