What is Macular Degeneration?
Macular degeneration is a chronic disease of the eyes caused by the deterioration of the central portion of the retina, called the macula. The macula is responsible for sharp central vision in the eye, which is needed for seeing objects clearly and for common daily tasks such as reading and driving.
The two most common types of macular degeneration are: Age-related Macular Degeneration (AMD) and Myopic Macular Degeneration (MMD). AMD is the most common cause of blindness among people aged 60 years and older in developed countries.
How MD distorts and blurs the central vision
What is AMD?
AMD is associated with ageing and it gradually destroys the sharp, central vision. In some cases, AMD advances so slowly that people notice little change in their vision. In others, the disease progresses faster and often leads to loss of vision in one or both eyes. AMD occurs in two forms: wet and dry.
What is dry AMD?
Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. The most common symptom of dry AMD is slightly blurred vision. Over time, central vision is gradually lost in the affected eye. While dry AMD generally affects both eyes, vision can be lost in one eye while the other eye seems unaffected.
What is wet AMD?
Wet AMD is the condition in its advanced stage. It occurs when abnormal blood vessels behind the retina start to grow under the macula. These tend to be very fragile and often leak blood and fluid, lifting the macula from its normal place at the back of the eye.
Damage to the macula happens very fast.
What is MMD?
Myopic macular degeneration, or MMD, is associated with high myopia. It is a result of an excessively long eyeball, which puts stress on the retina. MMD, like AMD, can be of the dry or wet type. In the dry type, light-sensitive cells break down and causes the macula to be less sensitive. When there is severe cell loss at the most central part of the macula, vision loss can be severe. In the wet type, abnormal blood vessels grow under the macula like in AMD. However, the prognosis for wet MMD is better than wet AMD.
How many people suffer from MD in Singapore?
There are no current figures on how many Singaporeans have macular degeneration but a community study in 1997 showed that one in four people aged 60 and above here suffered from the condition. Experts in Singapore believe that the numbers are much higher than reported. A study in 1997 found there were 154 unknown cases for every known case.
Can MD be cured?
While there is no cure for MD at the moment, early detection can prevent further deterioration and even improve vision in some cases.
Treatments available in Singapore are:
A. Laser photocoagulation
A surgical procedure involving the application of a hot laser to seal off abnormal blood vessels in wet MD. In the 1990's, laser treatment was the only therapy available for MD. A scar forms as a result of the treatment, and this scar creates a permanent blind spot in the field of vision. It is therefore not used when the abnormal blood vessels lie directly under the centre of the macula. Nowadays, its use is mainly restricted to sealing off abnormal blood vessels which lie outside the centre of the macula.
B. Photo Dynamic Therapy (PDT)
This treatment method uses a non-thermal, or cold, laser together with an intravenous light-sensitive drug to seal and halt or slow the progression of abnormal retina blood vessels. The drug accumulates in the abnormal blood vessels and the laser activates the drug in these vessels. The activated drug then causes a chemical reaction to close the abnormal blood vessels. Damage to the normal surrounding tissues is minimal unlike laser photocoagulation. Repeat treatment may be necessary to close the abnormal blood vessels more completely or permanently. Because PDT does not destroy the retina and cause a scar, it does not cause a blind spot in the field of vision. But early diagnosis of MD is key, because once vision is lost due to the growth of abnormal blood vessels, it usually cannot be reclaimed by this treatment.
Macugen is an anti-VEGF (anti-Vascular Endothelial Growth Factor) drug which works by targeting the proteins (VEGF) which act to trigger abnormal blood vessel growth and leakage. Anti-VEGF drugs are delivered directly to the eye by an injection, which is repeated every four to six weeks. Macugen was approved for use in Singapore in 2006 after successful clinical trials showed it reduced vision loss in 70 per cent of clinical trial patients. It is also very encouraging that the drug is effective for all kinds of wet AMD, whether in the early or late stages.
Approved in 2006 by the US FDA, this drug is currently awaiting approval for routine use in Singapore. About 95% patients with wet MD maintain their vision with it. Lucentis is by far the most effective treatment for AMD with about a third of patients actually gaining vision. This is an important treatment effect because to date, all other available treatments at best delay vision loss. However, not everyone will get such a positive outcome. The treatment, which is done by injections directly into the eye, is regarded as a major medical breakthrough.
Will I go blind?
No. MD never causes total blindness even though it may lead to legal blindness. Patients lose their central vision, but not their peripheral vision. Patients will therefore never lose their independence completely, unlike some patients with total blindness from other blinding conditions.
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