AMD--is a cure on the horizon? Macular degeneration is a major problem for an ageing population. OT's Nikki Withers investigates the potential of measuring macular pigment to prevent the progression of AMD.
Many people will say that prevention of a disease is better than a cure, but it would seem that the majority of doctors are only interested in evidence-based medicine, of which there are limited positive findings for the prevention of AMD.
However, one possibility is targeting risk factors for the disease. Well-known risk factors for AMD are age, family history, smoking and the presence of drusen. More recently, there has been accumulating evidence that measuring key components of the macular pigment could help detect people at risk of developing AMD. It has also been suggested that eye care professionals could then advise these 'at-risk' people to enhance their macular pigment through their diet or the use of supplements. However, robust evidence surrounding this area is minimal.
The study which brought hope
In 2001, the publication of AREDS (Age-Related Eye Disease Study) in the Archives of Ophthalmology caused great excitement among optometrists and ophthalmologists. It found that high-dose antioxidant vitamins and minerals taken orally reduced the risk of progression to advanced AMD by 25% and the risk of moderate vision loss by 19%.
Next month, the results of AREDS2, which will build upon the original study, are due to be published. This project will refine the findings of the original research by adding the two macular pigments lutein and zeaxanthin, as well as the omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The results could change the way that ophthalmologists and optometrists approach the monitoring and treatment of patients with AMD.
"The AREDS study is a very well formulated and very scientific, long-term and rigorous study, which people are very excited about," Mike Potts, a Bristol-based consultant ophthalmologist, told OT. "As consultants, we are interested in evidence-based medicine; we don't want to be seen to advocate quackery. But there is no doubt in my mind that doctors would be very happy to prescribe supplements when there is evidence that they can make a difference."
AREDS was a clinical trial, designed to investigate the natural history and risk factors of AMD and cataracts and evaluate the effects of high doses of antioxidants and zinc on the progression of the two conditions in people with AMD.
High levels were defined as: 500mg of vitamin C, 400IU of vitamin E, 15mg (or 25,000 IU) of beta-carotene, 80mg of zinc as zinc oxide and 2mg of copper as cupric oxide. Participants were given one of four treatments: zinc alone, antioxidants alone, a combination of antioxidants and zinc, or a placebo.
After an average 6.3 year follow-up, the study of nearly 5,000 people, aged between 55 and 80, concluded that high levels of antioxidants and zinc, significantly reduced the risk of developing advanced AMD by 25%. These same nutrients, however, had no significant effect on the development, or progression, of cataract.
Building on this, the purpose of AREDS2 is to evaluate the effect of the macular pigments lutein and zeaxanthin, as well as the omega-3 fatty acids DHA and EPA, on progression to advanced AMD and/or moderate vision loss. The study will also build on the original finding by evaluating the effects of eliminating beta-carotene and reducing zinc from the original AREDS formulation.
The results of AREDS2 will be of great interest to many professionals who are currently unsure of the benefits of measuring macular pigment to identify at-risk patients.
"As a clinician, I don't currently measure macular pigment, but I think that it is an important variable that we should be aiming to measure," said Mr Potts. "I am aware that there are machines out there to measure them, but there is controversy about which machine is the best to do it, and what benefit they have."
Mr Potts predicts that protecting against, and supplementing for, AMD is going to be a multi-factorial story. "The solution for macular degeneration will involve family history, smoking, the appearance of drusen and the macular pigment," he said. But while there is little robust evidence for this, and until the results of AREDS2 are published, Mr Potts remains slightly sceptical. "We are on the cusp of being able to do many things to help people with AMD. How these things will turn out, only time will tell."
So the question is, could measuring macular pigment be the solution that practitioners have been looking for to slow the ever-increasing prevalence of AMD?
The results of AREDS2 are due to be announced at ARVO's annual meeting In May.
Case study--Scott Mackie
'Macular testing improved my practice, both commercially and clinically'
Optometrist Scott Mackie co-owns two practices in Scotland. Six months ago, he acquired a macular pigment screening device--the MPS II from Elektron Technology (pictured opposite with patient)--and he says that he has already made his money back several times over.
"The MPS II costs 6,000[pounds sterling] (there's a launch offer of 4,000[pounds sterling] which I paid) so essentially you would need to see 200 patients at 20[pounds sterling]. It's a cost-effective piece of equipment, adding value to the patient and practice."
The MPS II is a portable screening device which enables early detection of patients at risk of AMD. The machine can calculate a patient's macular pigment optical density in less than two minutes per eye. To do so, the minimum for the peripheral curve is estimated by a formula which takes into account the age of the observer. A data quality algorithm then analyses the graph points and reports back on the validity of the results.
Mr Mackie says that he looks at the results of the macular pigment screening in conjunction with family and general health history. "You can help prevent drusen getting worse," he explained. "If a patient has low macular pigment, you can advise them to improve their diet and recommend macular supplements. It's all about a change in lifestyle--more fruits and vegetables in the diet and more exercise."
He added: "We also give patients a leaflet explaining the role of diet and supplements on AMD, and reassure them that, now we're monitoring it, there's nothing to worry about--it just means the pigment levels are down and we will give some supplements to help."
Testing macular pigment
Several machines have been designed to measure patients' macular pigment optical density (MPOD). The results of these macular screening tests can enable people to make informed lifestyle choices in order to improve the amount of macular pigment present in the eye.
For Western Caucasians, MPOD values are as follows: Low <0.25; mid-range 0.25-0.55; high >0.55.
Patients with low levels will often be recommended to elevate their macular pigment levels through their diet, supplementation and other lifestyle choices. this doesn't necessarily mean that they won't develop AMD.
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|Title Annotation:||UPDATE; age-related macular degeneration|
|Date:||Apr 19, 2013|
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