Diabetic Eye Disease

Diabetic Eye Disease

DIABETIC EYE DISEASE
by Prema Abraham, MD

Dr. Abraham is director of vitreoretinal and retinovascular
services, at Black Hills Regional Eye Institute, in Rapid City, South Dakota.

Introduction

Diabetes is a common medical problem which

affects the body's ability to regulate blood sugar levels. Over a

period of years, high blood sugar will damage small blood vessels

in the body and often cause problems such as kidney failure,

sensory abnormalities in the hands and feet, and eye problems.

The focus of this presentation is to describe how diabetes

affects vision, what specific factors contribute to visual loss,

and the technological advances that are available today to

evaluate and manage diabetic eye disease. Although in the worst

cases an individual may suffer permanent loss of vision in one or

both eyes, it is important to remember that most diabetics who

carefully control their diabetes and get good eye care can

prevent many of the visual complications of the disease.

Diabetes is present in approximately three

percent of Americans, however individuals in special populations

such as Native Americans and the elderly are much more likely to

suffer from the disease. For example, nearly 50% of some Native

American groups are affected, and among the nation's elderly,

about 15% are affected. Because one form of diabetes (i.e.,

adult-onset, or type II diabetes) may be present in a person for

several years before the diagnosis is established, some of the

preventable complications may already be in the early or moderate

stages when the diagnosis is finally made and treatment

initiated.

What is Diabetes?

Diabetes is much more than having an elevated

blood sugar level. It is a complex endocrine disorder which can

affect many aspects of the body's metabolism which in turn have

detrimental effects on a variety of vital organs. Left unchecked,

diabetes may result in complete kidney failure and require the

use of hemodialysis. The disease also causes heart disease and is

a potent risk factor for heart attacks. Nerve endings can also be

severely damaged, leaving the patient with a painful burning

sensation in the hands and feet or causing numbness in the same

areas. This loss of sensation places the diabetic at increased

risk of hurting him/herself without being aware of the damage.

The numbness, along with the detrimental effects that diabetes

may have on the immune system, increases the risk of serious

infection. Eye damage from diabetes may include any one or a

combination of problems such as cataracts, glaucoma, loss of

night vision, double vision, eye infections, fluctuating vision,

and retinopathy, a broad category of problems affecting the

retina.

There are two categories of diabetes, one which

affects individuals at a younger age (juvenile onset, or type I)

and the other which affects middle-aged and elderly adults (adult

onset, or type II). Both types are associated with elevated blood

sugars but the complications of the disease may vary in severity

and rate of onset and progression depending on the type.

How Does the Eye Work?

To understand how diabetes affects the eye it

is important to know how the normal eye functions. The eye works

very much like a camera, with a focusing lens in the front and

the film in the back. In the eye, the retina plays the role of a

camera's film, receiving the image of the object at which the

camera is focused. The retina, which is actually a direct

extension of brain tissue, transmits the visual information

through the optic nerve to areas of the brain which process it

into vision. In a camera, no matter how clear or strong the lens

and how perfectly focused the image may be, if the film is not

working well the camera will not take good pictures. Similarly in

the eye, if the retina is diseased vision will be impaired no

matter how clear and strong the lens may be. Furthermore, if the

space between the lens and the retina is obscured with blood or

other material, vision will be impaired.

When a diabetic goes to the ophthalmologist,

the doctor looks carefully at the retina. With special

instruments the blood vessels which normally travel through the

optic nerve can be viewed as they branch out and nourish the

retina. One small but particularly important area of the retina,

called the macula, is sometimes referred to as the "sweet

spot" of the retina. This "sweet spot" is the area

responsible for detailed vision such as is required for reading,

driving, needle threading and other similarly detailed visual

functions. The remainder of the retina is for side vision -or

peripheral vision- and not useful for fine vision. In order to

maintain meaningful vision for activities such as reading it is

essential that the macula remain healthy and unobstructed. If the

macula does become damaged or covered with blood the eye does not

necessarily become blind. It is possible that the side vision

will remain fully functional but reading and identification of

faces will be extremely difficult or impossible. For example, it

may be possible to perceive that someone is approaching but

without the "sweet spot" it will be impossible to

visually identify that person.

What is Retinopathy?

Retinopathy is the general name given to

diseases of the retina. In diabetics, it can take a variety of

forms and may affect both type I and type II diabetics. Type I

diabetics are usually free of retinopathy for the first five

years after diagnosis because there is rarely much time between

disease onset and diagnosis. On the other hand, because they may

have had the disease for several years prior to diagnosis, type

II diabetics may already have diabetic eye problems at the time

of diagnosis or shortly thereafter.

The principal problem of the retina caused by

diabetes involves the very fine blood vessels which nourish the

nerve tissue. High blood sugar causes these vessels to become

damaged and then leak fluid and fatty material into the nerve

tissue of the retina. The retina becomes swollen and does not

function normally. This form of retinopathy is called background

or non-proliferative retinopathy. The medical term for swelling

is edema; when this process involves the "sweet spot"

of the retina, it is called macular edema.

Another, more serious form of diabetic

retinopathy, is called proliferative retinopathy. Like the

non-proliferative form, this form is initiated by high blood

sugars over a period of years. However, in the proliferative form

the damage inflicted on the small retinal blood vessels results

in impaired blood flow to the retinal tissue. Some vessels

actually close off completely and deprive an area of the retina

of much needed oxygen and other blood-borne nutrients.

Consequently, the oxygen-deprived tissue sends out a signal which

stimulates the growth of new blood vessels. Unfortunately the new

vessels are distinctly abnormal and are the source of many

serious diabetic eye complications.

How is Retinopathy Treated?

As with many chronic conditions, the best

management strategy is based on prevention. For the diabetic this

means careful and consistent blood sugar control. Equally

important to the diabetic individual is frequent eye evaluations

which may permit early detection and treatment of retinopathy.

When the eye doctor examines the retina of a diabetic patient and

evidence of retinopathy is discovered the next step usually

involves obtaining special photographs of the retinal blood

vessels. This process, called fluorescein angiography, utilizes a

fluorescent dye injected into an arm or hand vein which then

circulates throughout the body. When this dye flows through the

retinal blood vessels, a series of photographs can be taken with

specialized camera equipment. The photos help locate areas of

abnormal blood vessels and guide the treatment process.

One straightforward method for managing leaking

blood vessels is to seal them with a highly focused beam of laser

energy. In effect, zapping leaking retinal vessels stops further

leaking of material from the vessels thereby limiting the

detrimental effect on vision. When the angiogram identifies

discrete areas of leaking vessels the laser treatments can be

confined to these specific areas. This is called focal treatment.

When the leaking is not due to one or two specific areas a more

broad treatment is required.

When the problem of leaking vessels is

widespread and excess fluid accumulates in the retinal tissue it

becomes necessary to apply laser treatment scattered over a

larger area. This is called grid treatment, since the laser spots

are applied in a grid pattern. This method, like the focal

treatment described above, is useful in the treatment of macular

edema.

In either situation the goal of treatment is to

stop the vessels damaged by the diabetes from continuing to leak

and to stop the progression of the visual impairment.

Unfortunately this treatment cannot restore vision that is

already lost.

The other, more serious form of diabetic

retinopathy, proliferative retinopathy, is also treated with a

laser. However, whereas the treatments in the non-proliferative

form are directed at sealing leaking vessels and not destroying

tissue, the objective in the treatment of proliferative

retinopathy is to actually destroy unhealthy, damaged retinal

nerve tissue. To accomplish this, a deeper laser burn, of larger

size, is used. This may seem counterproductive to the

preservation of vision, but the outcome of these destructive

treatments does ultimately minimize the cumulative loss of

vision. Remember, it is the blood and oxygen deprived retinal

tissue that stimulates the growth of abnormal vessels which never

provide any benefit to the retina.

Destroying the unhealthy retinal tissue

eliminates the stimulus for the growth of new, abnormal vessels.

These abnormal vessels are fragile and can bleed into the

interior of the eye, obscuring vision. Diabetics with

proliferative retinopathy may awaken in the morning with new

floaters or other visual changes because of bleeding which

occurred during the night. Because of rapid eye movements

associated with dreaming, diabetics are particularly vulnerable

to the breaking of the abnormal vessels while sleeping.

Treatment of proliferative retinopathy is

accomplished by applying hundreds of destructive spots of laser

across much of the peripheral retina. Even though there is

relatively widespread treatment there is very little, if any,

sensation of fine visual loss because only the side viewing

retina is treated. Furthermore, the area of the retina being

treated is already diseased due to the diabetes. Patients may

notice a reduction in side vision or night vision and difficulty

with light/dark adaptation following this type of treatment. This

treatment is called panretinal photocoagulation or PRP, and

usually requires multiple treatment sessions to complete. As

mentioned above, laser treatment of proliferative retinopathy is

directed at preventing progression of vision loss and does not

result in recovery of vision already lost.

Today, new multi-wavelength lasers are

available which permit the surgeon to select the most appropriate

type of laser beam for the specific problem the patient may have.

This flexibility helps the surgeon maximize the beneficial

effects while minimizing the detrimental effects of laser

treatment.

Another complication of proliferative

retinopathy is the formation of scar tissue in the eye associated

with the growth of the abnormal vessels. As the scar tissue grows

it may pull on the retina and tear it off of the back of the eye.

This is called a traction retinal detachment and can be quite

severe. A traction retinal detachment may cause severe loss of

vision. In some cases it ultimately results in loss of the eye

altogether. Panretinal photocoagulation, by destroying blood and

oxygen deprived retinal tissue, reduces the stimulus for abnormal

blood vessels growth thereby limits the development of scar

tissue. In turn, less scar tissue translates into reduced risk of

retinal detachment.

What Other Treatments are Available?

In some cases bleeding into the eye may occur

despite laser treatment. If the amount of bleeding is significant

it can obscure vision. When this happens the blood can be

surgically removed in the operating room by a retinal surgeon. In

addition to removing the blood from within the eye, this surgery

has the added benefit of removing the entire jelly-like substance

which normally occupies the space in the eye chamber. By removing

this substance, the structure into which the abnormal vessels

grow is eliminated, and therefore future abnormal growth is quite

rare. The jelly-like substance is called the vitreous and the

procedure is called a vitrectomy. Vitrectomy combined with other

microsurgical techniques is also the procedure used to repair

traction retinal detachments.

Conclusion

Diabetic eye disease is an important cause of

severe vision loss in patients under age 60. However, with

regular eye exams problems can be detected in their early stages.

Early detection means that treatment can be started before

serious visual loss occurs. All patients with diabetes should

have their eyes examined at least once each year, and individuals

with more advanced disease may benefit from more frequent

evaluations. These exams should be performed by an experienced

eye care professional who will dilate the pupils with special eye

drops so that the entire retina can be more easily viewed. If

laser treatment or other surgery is required, then one may be

referred to a retinal specialist.

Through education and cooperation with medical

and eye care professionals, the diabetic patient can remain

optimistic about successfully managing the disease and its ocular

complications.