Wet vs. Dry AMD: What's the Diff?
Not only is there more than one type of age-related macular degeneration, but the conditions are treated differently, too. We spoke with a top ophthalmologist to learn more.
We bet there's a good chance you've heard of age-related macular degeneration (AMD), a condition that can lead to vision loss. But did you know that there's more than one type...and that the more advanced form is actually more treatable?
We got to the bottom of these and other AMD questions with Peter E. Weseley, M.D., a clinical associate professor at NYU Langone Health who is a retina specialist in New York City. Dr. Weseley works with people who have AMD every day. Here’s what he told us.
What makes dry AMD different from wet AMD? Is one worse than the other in terms of vision loss?
"First, these are not two different diseases but different manifestation of the same condition. By way of background, many people think that "macula" is a disease. It is actually just a part of the eye—the center of the retina, which lines the back of the eye and senses the image you’re focused on.
Very roughly speaking, the macula is like the sensor in a digital camera. The thing is, we pay almost all of our attention to the very central part of our field of vision, which corresponds to the macula. A small area of damage in the macula produces symptoms that are way out of proportion to the size of the affected region.
Now, back to dry vs wet: In dry AMD, the layer behind the macula, called the retinal pigment epithelium (RPE), starts to function poorly and cells start dying off. Early on, people typically have no symptoms, but examination of the eye will reveal drusen, which are little bumps under the retina that contain debris the RPE cells ought to be removing.
At this stage, mild or even intermediate dry AMD isn't really a big deal. Some of these patients will go on to develop advanced dry AMD in which large areas of cells die off in the RPE, causing blind spots (scotomas). Severe dry AMD can be quite awful, with substantial central blind spots that can make reading and driving impossible.
Wet AMD is a superimposed problem in which abnormal blood vessels and scar tissue develop behind the macula. This abnormal tissue leaks fluid and blood beneath and into the retina. The ensuing swelling in the macula, called macular edema, is what gives rise to the term "wet." Wet AMD, also called neovascular or exudative AMD, can lead to severe loss of central vision much more rapidly than dry AMD can."
What causes one versus the other?
"As to the cause, we are more ignorant than we would like to be. Over the last decade or so it has become clear that certain gene variants predispose some people to AMD. Also, smoking and heart-unhealthy diets seem to increase the risk of AMD. There is no clearly defined difference in factors that predispose you to dry versus wet AMD."
Are there gender differences in the two conditions? Ethnic differences? Different risk factors?
"There are no gender differences, but there are definitely ethnic differences. People of white European and ethnic Chinese origin have relatively higher risk for both types of AMD, and people of African origin relatively low risk."
People with dry AMD can progress to wet AMD. Over what period of time does that typically occur? Is it a certainty?
"Many people with dry AMD will never develop wet AMD. If they have certain high-risk characteristics, the risk is about 3% to 5% per year. But many people who are diagnosed with AMD don't have high-risk characteristics and may have a much lower risk."
Is there an easy way for a person to track vision changes that indicate progression? Or is it only possible to tell from the sophisticated imaging tests you might do in your office?
"Home monitoring can be quite helpful. Many patients who have AMD will be instructed to monitor an Amsler Grid at home. The idea here is that with your reading glasses on, from a reading distance, one eye at a time, you stare at the dot in the center for a couple of seconds. You should see the whole grid and all the lines should be straight and perpendicular. If parts of the grid disappear or are distorted, that suggests a problem in the macula, not specific to wet AMD.
There are some newer, higher-tech approaches, such as an at-home testing device called Foresee\Home, which haven't seemed to catch on widely, from what I have seen. Any home screening test can only raise the suspicion of wet AMD. It is a diagnosis that is always made by a combination of clinical exam and imaging tests."
Can you give us a brief overview of treatment for wet vs. dry? How have you seen treatment change over time?
"Dry AMD has thus far been a tough nut. Many drugs have been tried to at least slow the progression of atrophy that occurs with severe dry AMD. Most have failed outright, and the others have had slightly promising results at best in early stage trials. People have tried transplanting retinal-pigment epithelium cells and have gotten over some technical obstacles but have not achieved anything that I would consider a successful treatment.
A combination of vitamins and minerals was shown in the AREDS study and its follow-on, AREDS 2, to reduce the risk of developing wet AMD in high-risk dry AMD eyes.
Clearly the biggest thing in AMD thus far, and it is huge, is the development of drugs that are effective in treating the wet type of AMD. All the drugs currently used act by blocking the effect of a chemical called vascular endothelial growth factor (VEGF), which stimulates growth of abnormal blood vessels and scar tissue behind the macula. These drugs must be injected directly into the eye repeatedly, and typically for the patient's lifetime.
The typical frequency for injections is between once monthly and once every three to four months. These drugs have dramatically improved the outlook for people who have wet AMD, so long as treatment is started early in the course of the disease. This is why home monitoring and prompt evaluation by a professional are so important when you experience blind spots or distorted vision."
When you diagnose someone with wet AMD after they’ve had dry AMD, what are the typical questions you get?
"I always try to remain positive, and I think this is appropriate given the historical context. I explain the nature of the condition and that, without treatment, about 90% of people with wet AMD lose vision dramatically, leaving them unable to recognize faces, read, or drive. But fortunately, I tell them, there are now treatments that can almost always avoid this fate. That way, when I get into the details of the treatment—eye injections—I hope it doesn’t seem so bad to them.
Some people are worried that they will become completely blind, and I assure them this is an extremely uncommon outcome. Much more commonly, people get stuck on two issues. The first is the very idea of getting injections in the eye. A lot of people think it won’t be possible without being under anesthesia. Right before the first injection, most people express say they are terrified. Immediately after, most people say exactly the same thing: “That’s it?”
I think because I give people a lot of info at their first visit with the new diagnosis, a lot of the words I say after “injections in the eye” tend to vanish. Sometimes, someone accompanying the patient on the first visit, or the patient at a subsequent visit, asks how long the treatment will continue, even though I’ve previously explained. Then I repeat the explanation: For most people, the treatment goes on as long as they do, with the variable being how frequently they’ll get injections, as opposed to for how long."
Can either condition be reversed?
"Dry AMD cannot be reversed. Wet AMD, when treated early, frequently can be reversed to a certain extent with anti-VEGF injections."
As a practitioner who deals with AMD every day, what are your top three reasons for optimism when it comes to dry or wet AMD or both?
Knowledge is cumulative. As a community, we understand much more about these diseases that we did just a few years ago. Many leads that might contribute to effective treatments are being explored, and some of them couldn't have been imagined a generation ago because the basic science wasn’t there.
Intelligent research. There are a lot of really smart, patient, and persistent people working on these problems.
Money. There's a ton of money to be made by anyone who develops better treatments than we currently have for these diseases. Some of the current medications have sales over $1 billion per year. That's a big carrot.