DISORDERS OF THE RETINA
The retina is a micro-thin membrane that lines 75% of the back of the
inside of the eye. It is embedded with millions of light sensitive nerve
cells that capture images that are focused on it by the cornea and the internal
crystalline lens. The images are transmitted to the brain via
the optic nerve, where they are interpreted, and sight is achieved. The following
disorders affect the retina and/or its components:
Glaucoma is a disease process that has many forms. The end result of all these
forms, if not treated, is always the same. The optic nerve, which collects light
from the retina and delivers the information to the brain, wastes away.
Some forms of glaucoma involve "high pressure", while others do not. The only known
effective treatment for preserving the optic nerve and preventing further damage,
however, is to lower the pressure inside the eye, by medication or surgery.
Glaucoma is fairly common among the population over the age of 35, affecting 2 of
every 100 people. The number of people affected by glaucoma is expected to rise
dramatically as our population of baby-boomers ages. Risk factors for developing
glaucoma include: a history of high blood pressure, diabetes, a blood relative with
the disease, and being of African-American descent.
Because the early stages of glaucoma have no obvious symptoms, the only way to
detect it is through an eye examination. Intraocular pressure and optic nerve
health are always assessed during a comprehensive exam. Since there
is no prevention for glaucoma, yearly examination, particularly in those over the
age of 35, is highly recommended.
AGE RELATED MACULAR DEGENERATION (ARMD)
The macula is in the center of the retina, and is responsible for 20/20 vision.
When the eye is turned to look at something, it is being positioned so that light focuses directly on the macula.
An eye that has macular degeneration has lost varying degrees of central vision, but peripheral vision is not affected.
ARMD generally begins to affect people over the age of 50. There are two forms: a "dry" form and a "wet" form.
The "dry" form of ARMD accounts for about 90% of all cases. It is not treatable, but is also the milder of the two forms. The retinal cells in the macula simply "wear out" in a process that is usually very gradual and may affect one or both eyes. Symptoms include distortion of straight edges, such as door frames or telephone poles, or the appearance of small, dark spots that obscure part or all of central vision. Management of dry ARMD is aimed at learning to optimize the use of remaining peripheral vision.
The "wet" form of ARMD accounts for about only 10% of all cases yet is responsible for about 90% of all serious vision losses. The means by which vision is affected is very different from the dry form.
A layer of tissue, filled with tiny blood vessels, underlies the retina and provides its nourishment. For unknown reasons, this tissue begins to degenerate, and small leaks begin to form. Swellings, breaks, and lesions form within the retina, causing damage to the light sensitive nerve cells. If the affected nerve cells are within the macula, rapid deterioration of central vision can result.
Lasers are used, with varying degrees of success, to either cauterize the leaking tissue, or "tack down" detaching retinal tissue. The goal is to save what central vision remains.
Protecting the eyes from sunlight and antioxidant vitamins may be preventive measures to preserve retinal health. Of course, regular eye examination is by far the best way to detect small changes in the macula; treatment can much more effective if begun as soon as possible.
RETINAL TEARS AND DETACHMENTS
There are two related types of serious retinal damage that can cause partial and temporary loss of vision, and also lead to total loss of vision if not detected and repaired in time. These are retinal tears and retinal detachments.
Retinal tears have a variety of causes, but the most common is because the gel-like substance that fills the back of the eye, known as the vitreous humor, contracts and pulls away from the retina. Sometimes, as the vitreous peels away, it pulls part of the tetina as well, creating a tear. These usually occur in the peripheral retina, and don't harm vision unless they go untreated, and progress into a retinal detachment.
A retinal detachment occurs because vitreous fluid seeps into a tear, and splits the retinal layer apart, which destroys light-collecting nerve fibers. This can lead to extensive, and even total blindness. Retinal detachments can also be caused by injury, complications of diabetes, tumors, or inflammation.
Symptoms of retinal tears include flashes or bright arcs of light that are present even when the eyes are closed. The appearance of floaters (spots strung together by a web-like thread) or showers of spots can also indicate a tear or detachment. Objects may appear wavy, or part of peripheral vision may be blocked by a dark splotch. If any of these symptoms occur, the eyes need to be evaluated as soon as possible; it is imperative that retinal trears be treated as soon as possible to prevent a detachment.
The usual treatment of a tear is by using a laser to seal it so that fluid doesn't seep through it. This treatment is painless, takes only a few minutes and is usually performed in a doctor's office.
Retinal detachments require surgical repair, and although most procedures are successful at repairing the eyeball, vision cannot be restored where a detachment has occurred.
With retinal tears and detachments, as with most health problems, prevention is better than any cure. Regular examinations are essential in detecting signs of all types of eye damage.
Diabetic retinopathy, to some degree, affects 90% of all people who have diabetes mellitus. Fortunately, a relatively small percentage will experience serious vision problems, but some 5,000 diabetics per year will totally lose their vision.
There are two types of diabetic retinopathy: non-proliferative and proliferative. The proliferative type is the advanced stage of retinopathy and only affects about 5% of diabetics. It mostly affects those who have had the disease for 25 years or more.
Non-proliferative retinopathy involves the weakening of the tiny blood vessels that nourish the retina. The vessels begin to leak, which diminishes the retina's nourishment, and can hemorrhage and leak fatty acid or protein deposits. If this occurs in the peripheral retina, or is in the early stages, a person is usually unaware of what is happening. However, if it happens in the macula, which is responsible for central, fine-tuned vision, serious vision problems can result.
In proliferative retinopathy, blood vessels leak components into the vitreous humor (the clear fluid that fills the inner cavity of the eye), which causes cloudy vision. This is further complicated when scar tissue forms from the damaged blood vessels. This creates a "pulling" action on the retina within the vitreous, and can lead to a retinal detachment, which is very serious.
Individuals with non-proliferative retinopathy may experience very little or no perceivable problems. Those with the proliferative form will most likely notice some deterioration in vision, which includes cloudiness, distortion, or loss of central vision. Individuals should NOT rely on their own ability to detect problems. This can only be accomplished through a complete eye examination.
Treatment for retinopathy may include simple monitoring, as is the case for the non-proliferative form, or lasers may be used to cauterize leaking blood vessels before progression to the proliferative form occurs.
As with all serious eye disorders, early detection is crucial for the most effective treatment, especially in diseases of a progressive nature such as diabetes. Patients with diabetes are urged to have complete eye exams at least once a year.