The human eye is a wondrous, and wondrously complex, device. Complexity, however, comes at a price, and while our eyes are relatively small organs, they're prone to an outsized number of ailments, from cataracts and diabetic retinopathy to color blindness, glaucoma, and more.
One particular diagnosis—age-related macular degeneration, or AMD—often sparks a special fear in patients. And no wonder: There is no cure for AMD, in either its earlier "dry" form or the more advanced "wet" stage. (See more on the difference between the two below.) But despite its fearsome reputation, there are plenty of reasons for those diagnosed with the condition to look ahead with optimism.
Most patients will not suffer from advanced AMD, which can sometimes result in legal (although not complete) blindness, says Jayanth Sridhar, M.D., an assistant professor of clinical ophthalmology at the Bascom Palmer Eye Institute of the University of Miami's Miller School of Medicine in Florida. And with timely treatment, he says, "the majority of AMD patients maintain functional vision."
If you or someone you love has been diagnosed with AMD, understanding exactly how the disease develops can help you stay one step ahead. Here's what you need to know.
What Is the Macula?
The macula, put simply, controls our sharp, central vision. Part of the retina, it's located at the back of the eye and is packed with light-receptor cells. When the macula is damaged by AMD, whether suddenly or gradually, vision can blur, straight lines might appear wavy, and blind spots can develop in the center of one's field of vision. Left untreated the condition will, in almost all cases, impact activities that rely on central vision, including cooking, driving, reading, and even recognizing faces.
There is currently no consensus on why some people get AMD and others don't. According to the Mayo Clinic, "no one knows exactly what causes dry macular degeneration" but research suggests that both heredity and environmental factors play a part. Caucasians and people who are overweight, smoke cigarettes, are more than 50 years old, or have high blood pressure are at increased risk, as are those with a family history of the disease.
Dry AMD: Early Stage
"Dry" AMD is the most common form of the disease, affecting somewhere between 85% and 90% of patients. (According to the National Institutes of Health, approximately 11 million people in the United States have AMD, most over age 50.) Dry AMD usually progresses quite slowly; people can live with the condition for years without discomfort or symptoms that suggest they need treatment.
The disease, meanwhile, is marked by three distinct stages. "The vast majority of AMD patients start off with the dry form, which in its earliest stage is characterized by the build-up of drusen, or fatty deposits underneath the retina," says Priyatham Mettu, M.D., an ophthalmologist and retinal specialist at Duke Eye Center in Durham, NC. Drusen is basically a form of debris that accumulates either because the cells are sick, or because a patient's ability to clear the debris is failing, says Dr. Mettu. "At the earliest stage, about half of patients are asymptomatic—they don't really have a lot of vision problems," he adds.
The other half of early AMD patients, however, often have significant trouble seeing in low light, says Dr. Mettu: "What that means is that trying to read a menu in a dimly lit restaurant, for instance, can be a real challenge."
When they do occur, early symptoms might include dark or blank spots in the center of one's field of vision, or a dulling or dimming of colors–the result of light-receptor cells in or near the fovea, where visual acuity in the retina is highest, atrophying or dying off. Upon diagnosis, a doctor might recommend one of several "AREDS" (Age-Related Eye Disease Study) antioxidant supplements; two large clinical trials sponsored by the National Eye Institute in 1999 and 2006 showed that certain antioxidant vitamins and minerals helped slow progression of the disease.
Dry AMD: Intermediate Stage
The intermediate stage of dry AMD is characterized by larger-sized drusen. At this point, some patients might experience mild vision loss or might require, say, a brighter light while reading, but in the majority of cases, intermediate AMD is far from debilitating.
A quick primer on drusen, which are often described as either "hard" or "soft": Those characterizations are not, in fact, based on texture, but on the drusen's appearance. "Hard" drusen are small and well-defined; their presence in the retina indicates a lower risk of vision loss than the presence of "soft" drusen, which are larger, tend to cluster together and, according to the American Academy of Ophthalmology, have edges "that are not as clearly defined as hard drusen." Their larger size and their tendency to bunch together, especially near the center of the retina, can distort vision. A person with a few hard drusen has significantly less chance of losing some of her central vision from AMD in a five-year timeframe than a person with numerous, larger soft drusen.
Ultimately, while patients with intermediate dry AMD might not experience significant vision loss or dramatic symptoms, they are nevertheless at increased risk of developing the advanced stage of dry AMD, or developing wet AMD, both of which are legitimately serious conditions.
Dry AMD: Advanced Stage
The advanced stage of dry AMD is also known as "geographic atrophy," in which the fovea is compromised. Blind spots are a virtual certainty at this stage, and certain activities in which central vision plays a critical role, such as reading or recognizing faces, can become increasingly difficult.
That said, certain techniques (learning to see objects using peripheral vision, for example, rather than relying on central vision) and behaviors (using specific types of light bulbs for reading) can help patients counter some of this stage's more troubling manifestations.
As Dr. Sridhar notes: "Those who happen to have advanced dry AMD, which is about five percent of patients in the U.S, should know that there is a lot of encouraging treatment research going on today, including work with stem cell and gene therapies. And even in the worst-case scenarios, AMD does not typically result in total blindness unlike with other conditions we treat, such as glaucoma. Peripheral vision is almost always maintained, even with advanced AMD."
Also known as neovascular AMD, if left untreated "wet" AMD reliably causes more rapid and more serious vision loss than the dry form. With few exceptions, wet AMD develops after—or in the middle of—the intermediate stage of the disease. (A very small percentage of patients develops wet AMD independently of the dry form.)
There's simple reason the two forms of AMD are described as dry and wet:
"When I talk to patients about wet AMD, I describe a blood vessel sort of sneaking up from beneath the retina. In some ways that's a colloquialism, but it's also the reality," says Dr. Mettu. "We don't necessarily know when that vessel will form, or what part of the population is at greatest risk.
It's worth pointing out that it's not a normal vessel going haywire. It's a pathologic or abnormal vessel that grows from the retina's vascular bed. As it grows, it can break through into the retina. It can also leak fluid, bleed, and scar—all activities that are bad enough for the retina's light-sensing cells that they can get injured and even die, which can result in serious vision loss."
One of the most common symptoms? Straight lines appearing wavy or crooked. This can happen when fluid from leaking blood vessels physically lifts the macula, distorting vision. (Picture the way paint on a wall or a ceiling sometimes balloons out when water from a leaking roof or pipe pools behind it.)
Another aspect of wet AMD that sets it apart from dry is the speed with which it progresses. While the stages of dry AMD typically evolve slowly, over years or even decades, the wet form can, in some cases, develop with alarming rapidity. As the American Academy of Ophthalmology bluntly puts it: Wet AMD "is less common but much more serious" than dry. "You lose vision faster with wet AMD."
We know that sounds scary, but there's some good news in all of this: When caught early, wet AMD is highly treatable. Targeted eye injections of a medication known as anti-vascular endothelial growth factor (VEGF) can block the growth of the abnormal vessels that have been "sneaking up" beneath the retina. Yes, you do need the medication delivered directly into your eye, but the important part to remember is that it can save, and sometimes even improve your vision. (Need more help getting comfortable with the idea? We’ve got advice.)
What Now? See Your Doctor
Remember: Neither the wet nor the dry form of AMD is a death sentence for your sight. But the only way to ensure that you retain as much of your vision as possible, for as long as you can, is to visit your eye doctor early, and often.