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.
Risk Factors
There a number of factors both in and out of your control that can put you at increased risk for developing AMD.
There are two types of AMD, dry AMD and wet AMD.
What is Dry AMD?
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 on of the deepest layers of the retina due to a breakdown in its normal function.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. In the end stages, the entire central macula can be damaged leaving a blind spot.
As the disease continues to progress, the likelihood of it turning in to the more severe wet AMD significantly increases as well.
Diagnosis of Dry AMD
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 the eye doctor are critical for early detection.
Treatment of Dry AMD
Vitamin supplementation has been shown to slow down the progression of dry AMD and decrease the risk of conversion to wet AMD. This was shown in a large clinical trial called the AREDs trial. Your doctor may suggest you take a vitamin supplement that has the components studied in the AREDs trial.
What is Wet AMD?
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. The 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 months. Early detection is critical in order to start any treatments that might help preserve your vision.
What are the Symptoms of Wet AMD?
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, 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.
Will I Lose My Vision Completely?
Not likely. 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 rarely occurs because the disease rarely affects 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.
How Fast Does it Progress?
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.
How is it Diagnosed?
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.
How is wet AMD treated?
You and your retinal specialist will determine which treatment is best for you. The first line treatment for most patients is Anti-VEGF Therapy.
Anti-VEGF stands for Anti-Vascular Endothelial Growth Factor. VEGF triggers the growth of the abnormal blood vessels in the macula. Anti-VEGF drugs help prevent this from happening.
The two drugs currently available in Canada and covered by the provincial health plan are Avastin and Lucentis. These drugs need to be injected into the eye on a regular basis for optimum effect.
Anti-VEGF therapy is NOT a cure. Most studies have shown that with regular treatment, 90% of patients can maintain their vision. 30 – 40 % of patients have seen an increase in vision with treatment.
You and your retinal doctor will try to develop a treatment plan to best suit your specific condition. All patients respond differently to treatment and require different treatment frequency and duration.
On average, most patients require ANTI-VEGF treatment every 1-2 months to maintain their vision. In some patients, the treatments can be spread apart further or discontinued – but there is always a risk of recurrence with subsequent loss of vision. This balance should be discussed with your retinal doctor..