Age-related macular degeneration, also called AMD, is a deterioration of the macula, which is the small central area of the retina (layer at the back of the eye) that controls visual acuity. The health of the macula determines our ability to recognise faces, drive, read, watch TV, use a computer and perform any other visual tasks that require us to see fine detail. This disease is the leading cause of irreversible visual loss in individuals older than 65 years of age, which accounts for 8.7% of all cases of visual loss worldwide.
People never go completely blind from AMD. Because it affects only the macular the central vision can be poor enough that a patient is defined as legally blind but even so the peripheral vision is always retained. Many people with advanced AMD, while unable to read or drive, can still maintain their independence.
The symptoms relate to degenerative processes that are occurring at the macular and can affect both eyes. Although in some rare cases vision loss can be sudden, this condition usually produces a slow, painless loss of vision.
Symptoms of macular degeneration include:
- Loss of central vision; shadowy areas in your central vision
- Distorted images; images that were once clear appearing blurry.
- Dark spots may appear in your vision and enlarge.
- Straight lines may become distorted or curved.
- Colour perception changes, as colours can appear less vivid or darker.
If you're in the early stages of age-related macular degeneration you may not have symptoms.
Types of AMD
There are many categories of macular degeneration and these sub-divisions can be based on factors such as appearance and age at onset. The most common classification includes a subdivision of wet or dry appearance to the macular.
- Dry AMD
Dry macular degeneration affects the health of the retina (the lining of the eye which responds to light) and is the most common type (85-90% of all cases). With the dry form of macular degeneration, the metabolic end products of the vision cells, called 'drusen', deposit underneath the retina. Over time, dry macular degeneration can lead to scarring and thinning of the retina above, which may cause central vision loss over time.
Most AMD initially begins as the dry type and may later progress to the wet type in 10-20% of individuals.
- Wet AMD
The wet type always begins as the dry type. In wet age-related macular degeneration, abnormal blood vessels under the retina begin to grow toward the macula. Because these new blood vessels are abnormal, they tend to break, bleed, and leak fluid, causing problems with vision when looking straight ahead. Abnormal vessels that leak blood and fluid damages the macula and causing it to lift up and pull away from its base, which can lead to a rapid and permanent loss of central vision.
What Causes Age-Related Macular Degeneration
As the name suggests, age is the number one risk factor for age-related macular degeneration and therefore this condition is more prevalent in people over the age of 60. Although medical experts are not exactly sure what causes AMD other than aging, research suggests the two most significant risk factors that increase the chances of developing the disease include smoking and family history of AMD.
Due to the fact that the retina has a high rate of oxygen consumption, anything that affects oxygen delivery to the retina, such as smoking, can significantly increase your risk of macular degeneration. Smoking causes oxidative damage which in some cases contributes to the development and progression of AMD.
- Family history of AMD
Researchers have identified several genes related to this disorder, which means that this disease has a hereditary component. Although it is not possible to control this risk factor, knowing your family medical history is one way to learn whether you may be a genetic disposition to the disease.
While it is not yet thoroughly understood, alcohol intake, excessive sun exposure, obesity, diet and high total cholesterol levels are some of the other risk factors for AMD. In order to reduce the risk of age-related macular degeneration, The American Ophthalmology Association recommends that individuals over the age of 50 and/or have a family history of AMD should wear appropriate sun protection to limit ultraviolet exposure, maintain a nutritionally balanced diet, stop smoking, limit alcohol consumption, increase consumption of foods or supplements that contain antioxidants and have regular retinal examinations.
How is AMD Diagnosed?
Amsler Grid: During an eye exam an ophthalmologist may ask you to look at an Amsler grid (a simple square containing a grid pattern and a dot in the middle). This grid is used to help the ophthalmologist identify if you have any blank spots or any distortion in your central vision.
Dilated Eye Examination: During a dilated eye exam dilating eye drops will be applied to the eye to temporarily widen the pupils. This test will allow the ophthalmologist to look through a special lens at the inside of the patient's eye to examine if there are any changes in the retina and macula.
Optical Coherence Tomography (OCT): OCT is a standard investigation for the diagnoses and ongoing management of wet DM. OCT is a non-invasive diagnostic technique that renders an in vivo cross-sectional view of the retina.
- Anti-angiogenic Medications:
There are several drugs that prevent the growth of abnormal blood vessels and block the leaking from abnormal vessels that cause wet macular degeneration. These drugs are injected into the eye at 4 to 8 week intervals to cause the blood vessels to shrink. This treatment option may stabilise the condition in some patients and even improve vision.
- Photodynamic Laser Therapy: This type of treatment involves a laser and a special light-sensitive medicine that works when exposed to a certain type of light to damage your abnormal blood vessels.
Early Detection is Key
If you have any two of the risk factors listed above, it is very important that you schedule an appointment for a complete evaluation with an ophthalmologist, who may recommend certain preventative measures which can reduce the risk of vision loss from AMD. The eyes work together and when one eye loses vision, you may not notice changes in your vision because the other eye is still able to see. Therefore each eye must be tested on their own to identify changes in vision.
Although there is currently no cure for AMD, early detection is vital to save sight. The earlier you seek treatment, the more likely you are to have a better visual outcome compared to those who wait and put off having an eye exam. To book an appointment with one of the Auckland Eye ophthalmologists call 0800 25 53 93 .