Age-related macular degeneration (AMD) is an eye disease caused by deterioration of the macula — a small area in the centre of the retina (the light-sensitive part of the eye). The macula is responsible for making sure we can see things in front of us (‘central vision’) clearly and in detail. If you have AMD, you may have trouble seeing clearly. Age-related macular degeneration is one of the leading causes of sight loss for over-50s. There are two types: dry and wet.
Macular degeneration symptoms
Macular degeneration isn’t painful. In the more common dry type it progresses so slowly you may not even notice you have the condition until you experience a loss of vision. AMD affects activities requiring detail, such as reading and writing.
Dry AMD symptoms
The more common of the two conditions, dry AMD affects your ability to see fine detail. People with AMD commonly have a blurred area in the centre of their visual field. For example, this might cause a person to see the numbers on a clock face but not the hands. Over time, the size of the blurred area increases, while objects appear faded, and blank spots develop in the central vision. You may find it difficult to read, use your computer, watch the television, drive, etc.
Dry AMD is classed as an early stage of the disease and may result from the ageing or thinning of macular tissues. It’s diagnosed by the presence of yellowish spots, called drusen, that begin to accumulate in and around the macula. This tends to occur due to a build-up of waste products in the macula.
Dry macular degeneration risk factors and causes
Several risk factors for dry AMD have been recognised; the strongest is age.
The exact causes of dry AMD are unconfirmed, however systemic (relating to the whole body) risk factors may include:
- High blood pressure
- Family history2
Dry macular degeneration symptoms
Dry AMD symptoms tend to develop gradually. These can include:
- Visual distortions
- Reduced central vision in one or both eyes
- Dim vision
- Difficulty in adapting to low light levels
- Increased blurriness
- Decreased intensity or brightness of colours
Dry AMD usually affects both eyes. If only one eye is affected, however, you may not notice any changes in vision due to compensation by the other eye. Thankfully, since the condition doesn't affect peripheral vision, it rarely causes total blindness.
Through a period of several years, dry AMD may also progress to what’s known as late-stage geographic atrophy (GA). This is when there is a more widespread breakdown of retinal cells and can cause severe vision loss. This is the most advanced form of dry AMD.
Wet AMD symptoms
Wet AMD involves a sudden and sometimes dramatic decline in your central vision, usually in one eye. Typically, wet AMD develops in people who have already had dry AMD. It is very important that anyone who has unusual symptoms (such as straight lines appearing to be wavy or blurring of the central vision) contacts an optometrist as soon as possible.
Wet macular degeneration risk factors and causes
The exact causes of wet macular degeneration are not yet known, however, clinical research is currently underway to try and remedy this. As we have established though, wet AMD tends to develop in people who already have dry AMD.
Other factors that may increase the risk of wet AMD are similar to dry AMD, and include:
- Family history
- Heart disease
Wet macular degeneration symptoms
The symptoms of wet macular degeneration are similar to those of dry AMD. However, the start of symptoms for wet AMD can be much quicker and may worsen rapidly, so they tend to be more noticeable.
What causes age-related macular degeneration?
Dry AMD is caused by the gradual breakdown of light-sensitive cells in the macula (the central area of the retina at the back of the eye) over several years. Wet AMD is caused by the growth of blood vessels underneath the macula, which can leak or cause scarring. It is not known why this is, but it tends to happen as people get older.
As it’s an age-related process, it usually involves both eyes, although they may not be affected at the same time.
How is macular degeneration diagnosed?
One of the best ways to detect macular degeneration is during a routine eye test – so it’s important to have one regularly so we can detect changes over time. During your eye test, your optician will carry out a number of tests, like taking a picture of the back of your eye, or they might want to do an OCT scan to get a better view of the structures inside the eye. If your optometrist thinks that you have wet AMD, they’ll refer you urgently to a specialist or hospital for treatment.
Both the dry and wet forms of macular degeneration are detected using the same eye exam. Early and intermediate stages of AMD, however, tend to show minimal signs and symptoms. As such, a comprehensive eye test, sometimes using dilating eye drops, and a visual acuity test is normally required to detect the condition. If your doctor thinks that you have age-related macular degeneration, they may want you to undergo one or more of these exams:
Visual acuity and Amsler grid test
Standard screening tests for AMD include the visual acuity exam (reading letters from the letter chart) which measures how well you see at various distances, and the Amsler grid, which looks like graph paper. Your optometrist will investigate whether the lines on the grid look wavy or distorted to you, or whether there are any blind spots in your visual field. If you experience any of these sensations, it may be an indication of AMD.
Dilated eye exam
In a dilated eye exam, your doctor will dilate your pupils with eye drops to get a better view of the back of your retina. They will examine your macula through a magnifying lens, and check for signs of disease and optic nerve damage. A mottled appearance caused by pigmentary changes in the macula and the presence of drusen (yellow deposits) underneath the retina may indicate AMD.
Fundus fluorescein angiography (FFA)
Fluorescein angiography (FFA) allows an eye doctor to study the circulation within the retina and choroid in detail. In FFA, a yellow dye called sodium fluorescein is injected into a vein in the arm or hand, which enters the blood circulation in the eye via the ophthalmic artery soon afterwards. How fast it gets there depends on the rate of injection, your age, and your cardiovascular health.
After about a minute, successive photographs of the eye are taken using a special camera. If the photos show fluorescein dye leaking out of retinal capillaries into the retina, this may indicate blood flow and possible leakage (wet AMD) within the retina and choroid. This method of imaging takes about 20 minutes altogether and requires dilation drops.
Indocyanine green angiography (ICG)
ICG uses dye to examine the blood flow in the choroid. Although similar to fluorescein angiography, ICG uses indocyanine green dye that glows and is visible in infrared (non-visible) light. This makes the circulation in the eye’s deeper layers, as well as the distinct outlines of the vessels within the choroid, visible when photographed with an infrared sensitive camera.
The most common application of ICG is to detect the creation of new blood vessels in the choroid, which is a common sign of wet AMD. ICG is sometimes used to complement fluorescein angiography (FA). FA is often referred to as retinal angiography, while ICG is referred to as choroidal angiography. The procedure takes about 20 minutes and requires your pupils to be dilated.
Optical coherence tomography (OCT)
OCT is a commonly-used, non-invasive imaging method that generates a 3D image of the retina. In this method, infrared light waves are used to make cross-section photographs of the retina and choroid layer.
OCT provides extremely useful information about drusen, retinal structure, new blood vessels, and haemorrhaging because it allows experts to measure the many layers of the retina itself, giving the optometrist or ophthalmologist a comprehensive look into the health of your eye.
While undergoing OCT, you will rest your chin on a machine and look into a lens for a few minutes per eye. Because OCT is an optical method, which means that it uses light as its means of investigation, it allows your doctor to examine various properties of the eye, which interact with light, that can identify tissue structure and composition.
Fundus autofluorescence (FAF)
Even without the use of special dyes, parts of the fundus — the interior surface of the eye, opposite the lens and including the retina — can become fluorescent in certain conditions.
This has recently been found to have the potential as both a diagnostic indicator and a tool for monitoring the progress of AMD. FAF imaging can provide information about the health and function of the central retina as well as side vision (peripheral). It is now considered an important tool for evaluating AMD, macular dystrophies, retinitis pigmentosa, white dot syndromes, retinal drug toxicities, and various other retinal disorders. FAF may detect abnormalities beyond those detected on other tests, including in a fundoscopic exam, fluorescein angiography, or optical coherence tomography6.
AMD and vision loss can profoundly affect your life. This is especially true if you lose your vision rapidly. Even if you experience gradual vision loss, you may not be able to live your life the way that you used to. Therefore, it is essential that everyone above the age of 40 undergo a comprehensive eye exam regularly to help detect AMD early and manage it correctly.
Macular degeneration treatment
Treatment will depend on the type of macular degeneration you have. There is currently no treatment available for dry AMD, but the wet type can sometimes be helped, if it is detected early.
If there are signs of wet macular degeneration, your optometrist will refer you to the hospital for prompt treatment, which can involve injections and sometimes light therapy.
The connection between macular degeneration and cataracts
Age-related macular degeneration affects the macula in the back of the eye, while cataracts affect the lens towards the front of the eye. Both conditions are age-related and contribute to impaired vision, especially in people older than 60. It is possible to have one without the other; they are two separate eye diseases with different causes. However, they share more than one common risk factor, and sometimes occur at the same time, which can have a considerable impact on your vision.
1. American Macular Degeneration Foundation. (no date). What is macular degeneration? [Online]. Available at: https://www.macular.org/what-macular-degeneration [Accessed 2 September 2019].
2. Evans JR. Risk factors for age-related macular degeneration. Prog Retin Eye Res 2001;20:227-53.
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