Age-related Macular Degeneration (AMD)
As its name suggests, Age-related Macular Degeneration is a disease linked to age. Specifically, people over age fifty. In spite of the fact that AMD is the leading cause of severe vision loss and legal blindness in people over 50 in the Western world, it’s still relatively unknown. Knowledge is power. Take a few minutes to learn about AMD – it may help you in the long run.
AMD is a chronic, age-related, degenerative disease of the macula. The macula is a very small and specialized area in the centre of the retina. The macula allows you to see fine details directly in front of you such as words in a book or images on television. So while the entire retina lets you see that there is a book in front of you, the macula lets you see what is written in the book.
There are two types of AMD, dry AMD and wet AMD. Generally speaking, dry AMD progresses quite slowly and is usually less severe than the wet type. But both types damage the macula and both can take away your central vision, which means the images you see directly in front of you. With impaired central vision, you might not be able to do some of the things you normally take for granted, like reading, driving, a favourite hobby and more.
Early detection and intervention is key to preventing or delaying vision loss. In the case of dry AMD, unless it’s detected in a routine eye exam, you may not even realize that you have the disease until it reaches an advanced stage. This is due to its usually slow and painless progression over a period of years and the ability of one eye to compensate for any weakness in the other.
On the other hand, wet AMD can cause severe and irreversible central blindness, often within months, sometimes even weeks. Therefore, it is important to visit your eye doctor regularly, especially if you determine that you’re at risk.
There are a number of factors both in and out of your control that can put you at increased risk for developing AMD. Knowing what they are might inspire you to make certain lifestyle modifications that can help to reduce that risk. Some of the known and suspected risk factors that you can’t do anything about are:
- Age: Risk increases with advancing age; from 8.5% for people 43–54 years of age to a high of 36.8% for people over 75
- Family History: Up to 3 times greater risk within families (parents and siblings)
- Gender: Females are more susceptible
The following are risk factors that you can do something about:
- Diet: A diet low in antioxidant vitamins and minerals is a significant risk factor
- Excessive sunlight exposure
- High blood pressure
- Excessive weight/obesity
Obviously you can’t change everything that puts you at risk, but wherever you can, consider making any lifestyle changes that will reduce your risk.
Most of the time, AMD will begin as the less severe dry type and, for approximately 80% of people, it will remain that way. Dry AMD can develop in one eye or both.
The early stage of dry AMD usually begins with the appearance of drusen. Drusen are small white or yellowish deposits that begin to accumulate in one of the deepest layers of the retina due to a breakdown in its normal function. You will not be aware that these deposits are forming.
As the retinal layer continues to break down, an abnormal amount of drusen begins to build up. This build-up begins to disrupt the layers above it, eventually damaging the layer of photoreceptor cells (the cells that receive visual images from the lens), resulting in “blank” or blind spots in your central visual field.
As dry AMD progresses from early to late stage, more cells break down and begin to waste away.
At the same time, drusen continues to build up and eventually, additional, larger blind spots are formed. As the disease continues to progress, the likelihood of it turning into the more severe wet AMD significantly increases as well. In fact, approximately 43% of people with advanced AMD in one eye may develop advanced AMD in their remaining good eye over 5 years.
With this type of prognosis, it’s important to be proactive and do everything possible to slow the progression of the disease. Your eye doctor will work with you to develop a plan to do just that. What’s most important is keeping all of your scheduled check-ups because monitoring the progress of AMD can be one of the best defenses against severe vision loss.
Dry AMD might first be noticed during a routine eye examination by your eye doctor, or you might have made a special appointment because you noticed that something odd was happening to your vision. Either way, an official diagnosis of AMD should be left to an optometrist or ophthalmologist.
Since dry AMD develops quite slowly, it can affect the vision in your eye without you being aware of it.
That’s because your eyes and brain are very good at compensating for weakness. So if dry AMD is compromising vision in one eye, the good eye will adjust, making up for the other's deficiency. Regular visits to your eye doctor are critical for early detection and the preservation of your vision.
Treatment of dry AMD is focused on monitoring and slowing the progression of the disease. Your eye doctor may want to monitor your progress at specific intervals in his office, and you will also be told to monitor your vision at home with an Amsler Grid. You should also consider making any modifications to your lifestyle that will help to slow the progression of the disease. Your eye doctor will discuss all of these options with you.
Perhaps the most important thing you can do is heed your doctor’s advice about vitamin supplements. Specific high-dose ocular vitamin therapy has been shown to delay the progression of dry AMD and preserve vision. By doing so, the chances of progression to wet AMD may also be reduced.
The Amsler Grid is a useful and simple tool for monitoring your central vision. It’s a test that you can do at home. Its regular use will alert you to any changes in your vision.
How to use an Amsler Grid (repeat for each eye): Note: if you wear reading glasses, be sure to have them on whenever you take this test.
- Position the grid at a comfortable reading distance
- Look at the centre dot on the grid with one eye at a time, covering the other eye with your hand
- Make sure you stay focused on the centre dot
- As you continue to look at the centre dot, check to see that all the surrounding lines are straight and all the squares are the same size
- If any area on the grid appears blurred, distorted, discoloured or in any way abnormal or different from your last test, contact your eye doctor immediately
Wet AMD is so named because of the involvement of blood in the deepest layers of the retina. In a process called choroidal neovascularization (CNV), new and abnormal blood vessels spontaneously begin to grow beneath the retina and push their way up through it.
Imagine they’re like tree roots or weeds growing up through cracks in the pavement. Being weak and abnormal, these new vessels leak their contents of blood and fluid into the retina which separates and lifts up the other layers like a blister. This process finally disrupts the photoreceptors (the cells that receive visual images from the lens), leaving them unable to transmit visual signals to the brain. This results in “blank” or blind spots in the central visual field. Left alone, this process eventually results in the growth of scar tissue which, in turn, causes severe and permanent central vision loss. Perhaps surprisingly, there is no pain associated with the entire process. Although wet AMD can occur spontaneously, it’s usually preceded by dry AMD, which makes regular check-ups especially important.
Wet AMD is more aggressive than dry AMD and does not occur as frequently, accounting for approximately 20% of all AMD cases. It can cause rapid, severe and permanent central vision loss in a matter of weeks.
Early detection is critical in order to start any treatments that might help preserve your vision.
- Blurred vision
- Straight lines appear wavy or distorted (metamorphopsia)
- Blank spots in central vision (scotoma)
- Any combination of the above
You will probably be the first person to detect the onset of wet AMD when you notice that your vision has suddenly changed. If you already have dry AMD, you might first notice a change on your Amsler Grid test. If you're not aware that you have any kind of AMD, your vision might suddenly blur, you may see a blank spot in your visual field, or things that should be straight appear bent or wavy.
Often accompanying the distortion and vision loss is a decrease in contrast sensitivity, which is the inability to distinguish dark from light as pictured. A loss of colour perception is also part of AMD.
No. However the eventual outcome of untreated wet AMD can be severe and permanent central vision loss, with vision dropping to legal blindness or lower. In AMD, total blindness or darkness almost never occurs because the disease does not affect the entire retina, just the central macula. So while someone with AMD may experience extremely poor vision in their central visual field, their peripheral vision is not impaired.
Unlike dry AMD which progresses relatively slowly and may go unnoticed for years, wet AMD is more aggressive and can cause severe vision loss in a matter of weeks or months. The speed at which wet AMD progresses is dependant on a variety of factors. And once you have wet AMD in one eye, the chances of it developing in your other eye are significantly increased.
Only an AMD specialist, such as a retinal specialist, can make a definitive diagnosis; however your regular eye doctor can usually detect the presence of wet AMD based on your symptoms, medical history and a basic eye exam including a dilated retinal exam. That’s why regular eye exams are important because early diagnosis gives you a better chance at preserving more of your vision.
If your regular eye doctor suspects wet AMD, you will be referred to a specialist. There, you will most likely undergo a dilated retinal exam followed by Intravenous Fluorescein Angiography (IVFA), a series of specialized photographs of your macula. These photographs will show what types of changes have occurred at the back of your eye. Based on these pictures, your specialist will recommend a specific course of action.
Additional AMD and support information can be found through the following resources:
AMD Alliance International
Canadian Ophthalmological Society (COS)
Foundation Fighting Blindness Canada
The Canadian Association Of Optometrists (CAO)
The National Coalition for Vision Health
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