Features

The macula is the central part of the retina responsible for detailed central vision. Age-related macular degeneration (AMD) is a disease of the macula that results in loss of central vision. AMD is the leading cause of age-related blindness in the Western world. It is estimated that AMD affects approximately 417,000 people in the UK and 80,000 people in the Republic of Ireland.

The increasing prevalence of AMD worldwide is largely attributable to increasing longevity and lifestyle changes associated with Western society. It is predicted that the current AMD prevalence figures will double by 2020. People with AMD lose their ability to read, recognise faces, watch television, and drive, and, therefore, lose their independence and quality of life. In addition, the cost of vision loss and visual impairment to society and to health care providers continues to rise, with significant economic implications.

Macular pigment (MP) is a yellow pigment found at the macula. MP is composed of the dietary carotenoids lutein, zeaxanthin, and meso-zeaxanthin. MP absorbs short-wavelength (blue) light pre-receptorally and scavenges and neutralises free radicals. It is unsurprising, therefore, that this pigment is believed to protect against AMD, because both blue light damage and free radicals are known to contribute to this condition. There is now an increasing body of scientific evidence which supports such a notion. For example, recent research by the Macular Pigment Research Group (MPRG) (www.wit.ie/mprg) has shown that individuals between the ages of 20 and 60 years (without ocular disease), who are at increased risk of developing AMD (eg cigarette smokers, people with a family history of AMD, people with poor diets lacking in antioxidants, people who are overweight and so on) have a relative lack of MP.

Meso-zeaxanthin trials

Meso-zeaxanthin is only found at the macula, whereas lutein and zeaxanthin are also found in a typical diet, serum, and several other tissues throughout the body. Meso-zeaxanthin is not found in a regular diet however, it is generated at the macula following biochemical conversion from lutein, and it is also found in some foods such as seafood (eg shrimp and crab) and fish (eg trout and salmon).

Macushield is the only dietary supplement available that contains all three of the macular carotenoids, including meso-zeaxanthin. The importance of meso-zeaxanthin and its presence in MP can be summarised as follows: meso-zeaxanthin is the central portion of MP meso-zeaxanthin is a more powerful antioxidant than either lutein or zeaxanthin meso-zeaxanthin facilitates a wider range of short-wavelength light absorption meso-zeaxanthin is more closely related to vulnerable photoreceptors at an anatomic level than either lutein or zeaxanthin.

The MPRG, at the Waterford Institute of Technology, Ireland is about to embark on two clinical trials with meso-zeaxanthin in the form of Macushield. The first clinical trial will be conducted in a randomised, double-blind, placebo-controlled fashion and will be carried out on normal subjects (without ocular pathology). This trial is designed to investigate macular and serum responses to supplemental meso-zeaxanthin, lutein, and zeaxanthin (Macushield).

The second clinical trial will be conducted in a randomised, comparison- (lutein, zeaxanthin versus meso-zeaxanthin, lutein and zeaxanthin [Macushield]) controlled fashion and will be carried out on patients with early AMD (presence of drusen and/or pigmentary changes). This trial is designed to investigate retinal sensitivity changes and AMD-related pathology changes at the macula, if any, in response to MP augmentation.

These meso-zeaxanthin trials are essential to test, in full, the putative protective benefits that this carotenoid may offer our AMD patients, and individuals at risk of this condition. Also, recent case studies have shown that supplementation with Macushield results in significant MP augmentation in the central portion of the MP and resolution of centrally-located drusen, and improvement in visual acuity, in two patients with AMD.

These individual case studies are positive, but properly conducted clinical trials, such as those outlined above, are essential to further our understanding of the importance of MP, and in particular the role of meso-zeaxanthin, for ocular health and AMD prevention. ●

● Eithne Connolly is a postgraduate and Dr John Nolan head of the Macular Pigment Research Group, Department of Chemical and Life Sciences, Waterford Institute of Technology, Waterford, Ireland

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