Age-related macular degeneration (AMD) is the leading cause of blindness in people aged above 60 years in the developed world.
AMD gradually affects central vision and the macula, which is the most sensitive part of the retina.
There are two forms of AMD: wet and dry.
Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile, and often leak blood and fluid.
With wet AMD, loss of central vision can occur quickly. Wet AMD is also known as advanced AMD and is a cause of severe blindness in our senior population.
Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye.
As dry AMD gets worse, you may see a blurred spot in the centre of your vision. Over time, as less of the macula functions, central vision is gradually lost in the affected eye.
Patients with dry AMD are at higher risk of getting wet AMD. The three major risk factors for developing AMD are: age, family history of AMD, and smoking.
There are now effective treatments available for wet AMD with injections of anti-VEGF antibody drugs into the eye.
In Malaysia, however, patients often present late to their ophthalmologists, and their visual recovery is limited, even with treatment.
There is no treatment available for dry AMD.
There is a huge interest in looking at ways to prevent AMD in the general public and delay progression of disease in AMD patients.
Diet and nutrient supplementation especially have been the focus of intense research in the past 10 years.
Looking at supplements
The Age Related Eye Diseases Study (AREDS) was a landmark trial done in the United States and completed in 2006.
It looked at the effect of nutrient supplementation in preventing and delaying progression of AMD in over 4,000 patients.
The exact contents of the supplements were 500 milligrams of vitamin C, 400 International Units of vitamin E, 15 mg of beta-carotene (equivalent to 25,000 IU of vitamin A), 80 mg of zinc as zinc oxide, and two mg of copper as cupric oxide.
The study found that patients at high risk of developing wet AMD benefited from taking these supplements as it reduced their risk of getting the condition, compared to patients who did not take the supplements.
Patients at high risk of developing wet AMD were those with intermediate or advanced dry AMD, or those who already had wet AMD in one eye.
An eye doctor will be able to tell you what stage of dry AMD you have and whether or not you will need to take these supplements.
We should be cautious in supplementing our diets with the nutrients and doses used in the AREDS as many older people take prescription medications, over-the-counter drugs, dietary supplements, and herbal medicines.
High dose nutrients can interfere with medications and interact with other nutrients to decrease their absorption into the body.
For example, the zinc concentration in the AREDS formulation is at a very high dose and could cause copper deficiency anaemia. To prevent this, copper was added to the AREDS formulation.
People who are being treated for chronic diseases such as cancer, heart disease and diabetes, should not take high dose nutrients without consulting their doctors.
Self-medication with high doses of vitamins and minerals is not recommended!
The results of the AREDS raised many more questions, like whether zinc and beta-carotene can be eliminated from the formulation as both these supplements can have side-effects.
Many people were also interested in looking at the possible beneficial effect of adding dietary carotenoids like lutein and zeaxanthin, and omega-3 fatty acids to the formulation.
As such, AREDS 2 was started in 2008, and will hopefully refine the findings of the original study by adding the above supplements to the study formulation.
The main objective is to determine if these nutrients will decrease a person's risk of progression to advanced AMD. Previous observational studies have suggested that these nutrients may protect vision.
The results of the study are expected to be released in 2013.
More on diet
More on diet
Carotenoids are the natural pigments that give colour to egg yolks, tomatoes, green leaves, fruits, and flowers. They cannot be made internally in the body, and therefore, must be obtained from the diet.
Lutein and zeaxanthin are members of the carotenoid family. Beta-carotene is another type of carotenoid.
They serve as light-gathering pigments and protect against the toxic effects of ultra-violet radiation and oxygen. They also appear to protect humans against phototoxic damage.
Lutein and zeaxanthin are found in the macula, as well as the lens of our eye.
When taking orally, lutein and zeaxanthin are far more effective in penetrating the retina than beta-carotene.
However, AREDS did not include them and used beta-carotene, because lutein and zeaxanthin were not commercially available 10 years ago.
Another interesting finding of the AREDS involved the diet of the participants.
The participants were given either a placebo or the actual supplements, had their eyes checked annually, and were also required to inform investigators about their diet.
In terms of eating oily fish (rich in omega-3 oils), the effect on the progression of early AMD was found to vary depending on what supplements the participants were taking.
The researchers found that consuming higher levels of oily fish was associated with a reduced risk of progression of early AMD in people taking the placebo, but there was no significant effect of eating more oily fish on the progression of early AMD when participants used the supplements.
They also found that eating a low glycaemic index (GI) diet reduced the risk of progressing to advanced AMD, regardless of what supplements were being taken. Low GI foods release their sugars into the blood more slowly than foods with a high GI.
So, there is clearly a complex interaction between diet and supplements in the prevention of AMD.
My opinion on this is that a low GI diet with two to three servings of oily fish a week can help prevent AMD, and is probably more useful than taking supplements alone.
I apologize for the excessive medical jargon used today, but I wanted to share these key findings of this very important study with you.
Prevention of AMD is a complex area, and I don't believe that taking supplements alone will help.
Apart from the supplements I have mentioned earlier, there are many other supplements that are commercially available that claim to prevent AMD like bilberry, gingko, acai berry, turmeric, selenium, and bioflavinoids.
It is very difficult to assess these claims, and currently, the most convincing evidence still comes from the AREDS, which found that high dose antioxidants and zinc supplementation reduced the risk of developing wet AMD in patients who already had dry AMD.
Please also bear in mind that the AREDS was done on a predominantly white North American population, and their findings cannot be directly extrapolated to our Asian population.
As a general guide to AMD prevention, here are my top five tips:
1. Eat plenty of fruits and vegetables like spinach, carrots, broccoli, guava and papaya. Choose different coloured fruits/vegetables to ensure you get a good variety of nutrients.
2. Eat oily fish like tuna, salmon, mackerel or sardines at least twice a week.
3. Exercise regularly.
4. Avoid a high fat diet.
5. Avoid smoking.
Dr Fong Choong Sian is a consultant ophthalmologist while Goo Chui Hoong is a consultant dietitian. For further information, e-mail email@example.com. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care.