Age Related Macular Degeneration
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ARMD is condition that can occur in individuals above the age of 50 years. It tends to occur bilaterally but can affect only one eye initially. It is the leading cause of irreversible visual loss in the industrialized world and in Asia it is fast becoming a major cause of irreversible blindness. ARMD is condition that can occur in individuals above the age of 50 years. It tends to occur bilaterally but can affect only one eye initially. It is the leading cause of irreversible visual loss in the industrialized world and in Asia it is fast becoming a major cause of irreversible blindness.
What causes it?
Macular degeneration is caused by hardening of the arteries that nourish the retina. This deprives the sensitive retinal tissue of oxygen and nutrients that it needs to function and thrive. As a result central vision deteriorates. The central portion of the human retina contains a yellow pigment called the macular pigment. This pigment helps protect the sensitive receptors in the retina, particularly from the potentially harmful effects of blue light. The density of the pigment has been shown to be linked to diet and can be reduced in those who smoke.
The macula is the part of the retina that allows the eye to see fine details at the center of the field of vision. Degeneration results from a partial breakdown of the retinal pigment epithelium (RPE).
The RPE is the insulating layer between the retina and the choroid (the layer of blood vessels behind the retina). The RPE acts as a selective filter to determine what nutrients reach the retina from the choroid. Many components of blood are harmful to the retina and are kept away from the retina by normal RPE.
Breakdown of the RPE interferes with the metabolism of the retina, causing thinning of the retina (the "dry" phase of macular degeneration). These harmful elements may also promote new blood vessel formation and fluid leakage (the "wet" phase of macular degeneration).
This disorder results in the loss of central vision only -- peripheral fields are always maintained. Although loss of ability to read and drive may be caused by macular degeneration, the disease does not lead to complete blindness.
Types of ARMD
There are two main types of ARMD: the "dry" form and the "wet" form, based on the absence or the presence of abnormal growth of blood vessels under the retina known as Choroidal Neovascular Membrane. Most people with ARMD have the dry form.
Currently there is no proven treatment for the dry type, but the loss of vision tends to be milder and the disease progression is rather slow.
Approximately 10-15% of patients with ARMD have the wet form, where there is a growth of abnormal blood vessels under the retina, which can cause leakage, bleeding, and scarring, resulting in more rapid and severe vision loss. About 80% of severe vision loss is due to the wet form as compared to 20% due to the dry form.
The wet form can manifest in two types: classic or occult. Over 70% of patients with the wet form have the occult type.
What happens to Vision ?
Some people with macular degeneration notice that straight lines in a landscape - such as telegraph poles, the sides of buildings or streets, appear wavy. Other symptoms include blurring of type or a page of print, with dark or empty spaces that may block the centre of the field of vision.
This is an example of what a patient with advanced macular degeneration might see:
Straight lines may become distorted
The central part of the visual field may be missing
Reading may become very difficult
Fortunately, macular degeneration rarely results in complete blindness since peripheral vision is usually unaffected. Although activities that require sharp vision such as reading, sewing or driving can be difficult, most people maintain their independence and should be able to get around outside and perform most household duties.
There is (currently) no known cure, but there are many indications that a good diet and healthy life style (particularly not smoking) will considerably reduce the chance of suffering from ARMD.
It is possible to carry out a simple test, to see if you might be suffering already without even knowing about it. In the early stages vision loss is only small and the brain cleverly covers up the defects so you don't notice. The AMSLER grid is a simple visual test that you can carry out on yourself in a few minutes
Instructions for using the Amsler grid
- Test your vision with adequate lighting.
- Wear your reading glasses or look through the reading portion of your bifocals (if you normally read with spectacles).
- Hold the Amsler grid at normal reading distance (about 35cm).
- Cover one eye at a time with the palm of your hand.
- Stare at the centre dot of the chart at all times.
- Do not let your eye drift from the centre dot.
How to reduce the risks for ARMD?
- Eat foods rich in lutein and zeaxanthin (or supplements)
- Increase intake of fruits and vegetables
- Consuming fish (like tuna) more than once per week may be beneficial
- Reduce alcohol consumption (alcohol may deplete antioxidants and carotenoids in the body)
2) General Health:
- Decrease cardiovascular risk factors (hypertension, obesity, fats, and cholesterol)
- Reduce your Body Weight
- Gentle exercise is good for you - but don't overdo it.
- Stop or never start smoking! Smoking very seriously affects your health and vision in later life.
- Eye protection: Wear UV-blocking glasses/sunglasses (and preferably large or wrap-around types)
- Eye protection: Wear hats or caps with eye shielding brims
How do we treat ARMD?
There is as yet no outright cure for macular degeneration, but some treatments may delay its progression or even improve vision. These include:
Thermal Laser Photocoagulation
The benefit of this treatment is that it can prevent further degeneration of the macula. However, the laser treatment can damage healthy macula cells meaning that you might lose a little sight to save a lot. Laser treatment is only useful in about 10 per cent of people with wet AMD and this always where people have reported their symptoms early..
Transpupillary Thermoplasty (TTT)
It involves shining a laser light of low intensity and at a specific wavelength onto the affected area. It does not damage the overlying healthy retina and only affects the abnormal vessels in the Wet AMD.
Photodynamic Therapy (PDT)
With PDT, a light-sensitive dye (Visudyne) is injected into the bloodstream and is transported to the retina at the back of the eye. This chemical highlights the blood vessels that are growing abnormally. A low energy or 'cold' laser beam is then shone onto the macula. This makes the chemical react and destroy the leaking blood vessels without damaging the healthy tissue around the affected area in the back of the eye. More than one treatment is usually required. PDT is unsuitable for long-established wet AMD and cannot restore sight that has already been damaged by macular degeneration. PDT cannot be used to treat dry AMD.
Anti Vascular Endothelial Growth Factor (VEGF)
VEGF has been shown to be important in the formation of the new vessels in the Wet type ARMD. The most recent development in the treatment of ARMD is the availability of Anti VEGF's. These drugs inhibit the role of VEGF in the formation of new vessels. It is injected directly into the eye with a small needle. This procedure is called Intravitreal Injection and is done in the clinic under topical anaesthesia. Anti VEGF's has been shown to be able to treat all forms of the Wet type ARMD, with some good visual recovery. It is however, necessary to have repeated 4-6 weekly injections for about 3-4 month. Further re treatments may be necessary depending on individual cases.
Will my vision return to normal after treatment?
As stated earlier, there are no cures for ARMD at this moment. All the treatment options discussed are designed to preserve whatever vision this is left. However, some patients do gain better visual improvement after treatment depending on the severity of their lesions.