Age-related Macular Degeneration
By: Dr. Amjad Hammad
Age-related Macular Degeneration (AMD) is the leading cause of blindness and loss of central vision among adults over the age of 65. AMD is a chronic disease that affects the retina – the part of the eye that allows you to see fine detail — blurring your central vision. It can have devastating impact on your ability to read, drive, or engage in other activities of daily life. An estimated 15 million North Americans alone have AMD.
There are two forms of AMD, known as “dry” and “wet”:
- Dry AMD – Characterized by small yellow particles and pigment changes in the macula caused by cells breaking down. Over time, the deposits may grow together and harden, thereby interfering with central vision.
- Wet AMD – Occurs when abnormal blood vessels behind the retina start to grow under the macula. These blood vessels often leak blood and fluid. Wet AMD is the more advanced form of the disease and loss of vision occurs quickly.
Early Stage Wet AMD
End Stage Wet AMD
Most patients have what is called the “dry” form, in which the yellow deposits, called drusen, are present in the macula. In advanced stages, tissue death may lead to blind spots and loss of central vision. About 10 percent of people with AMD develop the “wet” form of the disease in which abnormal blood vessels grow.
The earliest signs of macular degeneration in the retina can be detected before you have any vision loss. This detection is facilitated by an eye exam in which eye drops are given to dilate the pupil of the eye.
Patients with macular degeneration are usually older than 55 years old, have signs of macular degeneration in both of their eyes and may have experienced some slow, insidious vision loss. Most have dry macular degeneration. Perhaps 85 – 90% of macular degeneration is of the “dry” variety.
Dry AMD usually occurs slowly, over time. The patient may notice a need for brighter light when reading. Other symptoms may include difficulty adapting to low light levels, increased blurriness of printed words, decrease in brightness of colors, or a blurred spot in the center of the field of vision. A dark blank or black spot in the middle of your vision can also be a sign of macular degeneration. This spot starts out small, grows over time and could eventually lead to legal blindness in your central vision but does not affect your peripheral or side vision. So you never become totally blind.
In contrast, visual changes in wet AMD occur more rapidly, resulting in an abrupt decline in central vision. Patients may experience visual distortions, such as straight lines appearing wavy, or objects appearing larger or smaller than they are. As in dry AMD, patients may also notice a well-defined blind spot in the center of vision.
You should also keep an eye out for early symptoms of macular degeneration. Here are some things to look for:
Watch for straight lines that appear broken, crooked, wavy, bent or distorted in your vision. One way to test your eye sight is to use an Amsler Grid.
Amsler grid as seen with normal vision
Amsler grid as seen with AMD
If the lines in the grid appear anything but straight and unbroken, you might be experiencing a typical symptom of macular degeneration.
However, this test is hardly sufficient to rule out the possibility that one has developed macular degeneration. Many people with macular degeneration may see no abnormalities on an Amsler grid, so don’t use this as a substitute for regular good dilated eye examinations of the retina.
Pay close attention to a decline in your central vision, both close-up and distant. People use central vision when they drive, read, look at faces or view pictures. Your central vision allows you to see details, colors and shapes more clearly.
AMD causes patchy vision that often interferes with visual efficiency
Regular dilated eye exams with an ophthalmologist are important, especially when you’re at higher risk for macular degeneration. If you are over the age of 50, an exam every one to two years is a good idea in order to look for signs of macular degeneration before any vision loss has occurred.
AMD is caused by the destruction of light-sensitive cells in the macula. The macula is the central portion of the retina in the back of the eye. The light-sensitive cells of the macula give us our ability to have sharp, detailed vision.
In a healthy eye, images are focused onto the retina and then converted into electrical signals that are sent to the brain for processing. During normal aging, yellowish deposits, called drusen, form under the retina. It is possible to have drusen with no accompanying loss of vision.
But as drusen increase in size and number, they can interfere with proper functioning of the retina, damaging or killing the light-sensitive cells of the macula. This is how dry AMD occurs.
The wet form of AMD occurs when blood vessels behind the retina begin to grow in an abnormal way. These newly formed blood vessels can then leak blood and fluid, causing the macula to swell. Again, the macula’s light-sensitive cells are damaged or killed.
The primary risk factor for AMD is age. The older you are, the greater your risk for macular degeneration. Also, people with a family history of the disease are at higher risk for macular degeneration, as are women, and people of European descent.
One way to check for AMD is to look at an Amsler Grid as shown earlier in this chapter. Cover one eye and stare at the black dot in the center. If the straight lines appear wavy or are missing you may have AMD.
A fluorescein angiogram is usually performed to demonstrate the presence of neovascularization. If present, therapy may be instituted soon, to prevent further vision loss. The earlier the diagnosis is made, the better.
Angiography is a diagnostic procedure in which a rapid sequence of photographs is taken to document the blood circulation of the retina. In this test, illuminated dye is injected into the body through your veins, usually in the arm, forearm or hand. As your blood flows, the dye gradually appears in the retina.
Since the fluorescein dye is a very bright yellow, the skin may appear jaundiced for a few hours and then the yellow color disappears. The dye is excreted through the kidneys causing the urine to be a bright yellow for 24-36 hours. The coloration of this dye is considered to be a normal result of the after effects.
I will photograph the retina and evaluate its appearance with the help of the illuminated dye. This analysis helps determine if the disease is present and how far it has progressed.
Normal eye as seen in fluorescein angiography
Dry AMD Wet AMD
as seen in fluorescein angiography
Optical Coherence Tomography (OCT)
This latest generation of imaging technology makes quicker and more accurate diagnoses possible. Instead of using acoustic waves as in ultrasound, OCT uses light to take cross section images of the retina and is 15 times more sensitive than conventional ultrasound.
Normal eye seen with OCT scan
Dry AMD seen with OCT scan
Wet AMD seen with OCT scan
B-Scan ultrasound is most useful when direct visualization of intraocular structures is difficult or impossible. Situations that prevent normal examination include lid problems, severe edema, corneal opacities, dense cataracts or hemorrhage. In such cases, diagnostic B-scan ultrasound can give valuable information on the status of the vitreous and retina.
Treatment and drugs
There is no known cure for AMD. However, through early detection and proper treatment AMD patients can protect their vision from further deterioration. More advanced stages can often now be treated, as well.
Currently, no medical treatments exist for dry AMD, but I may suggest strategies to slow its progression – taking vitamin or mineral supplements, for example.
It is extremely important to continue to get regular eye examinations, especially if you have been diagnosed with dry AMD. If you experience new symptoms, or your vision suddenly deteriorates, you should see a retina specialist right away.
A variety of medical treatments are now available for wet AMD. None of them are considered a cure, but they can help stop further vision loss. Treatment options include laser surgery, photodynamic therapy, or injections aimed at destroying abnormal blood vessels or preventing them from leaking. Most often, I treat “wet” macular degeneration with anti-VEGF intraocular injections.
Can AMD be prevented? Like most things in life, there is no easy answer.
Age and genetics are both linked to the likelihood of being diagnosed with AMD. Older people, those from a family with a history of the disease and those of European descent are at higher risk for macular degeneration. Unfortunately, there is nothing we can do about these factors.
However, some lifestyle factors are also known to increase your risk for AMD. If you alter these factors, you may decrease the chance of getting macular degeneration. The most important modifiable risk factor is cigarette smoking. Obesity, hypertension (high blood pressure), excessive sun exposure and a diet deficient in fruits and vegetables also might increase your risk.
Eliminating these factors, of course, not only may reduce your risk for macular degeneration, but for many other things as well, including cancer and cardiovascular disease.
While no cure exists for AMD yet, treatments can slow its progression if it is detected early.
Most important of all keep this in mind: You can still have a good quality of life, even with a diagnosis of macular degeneration. Even though AMD makes it harder to see, it only rarely leads to complete blindness. While it can be a difficult condition, it is usually not as devastating to people as they fear when initially diagnosed.
Most patients are able to keep some of their vision, and they learn to adapt, finding ways to use their remaining vision to its fullest capacity. Millions of Americans are living healthy and independent lives, despite having AMD.