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Monthly Health Review, July 2003
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Age Related Macular Degeneration (AMD)
Eyes have the amazing ability to capture the patterns of light in the
world around us and turn them into pictures on the retina just as a camera
captures images on film.
Vision is one of the senses that allow us to carry out our daily tasks
with relative ease; however, most people take the health of their eyes
for granted. Looking after the health of the eyes whenever possible is
important and it is a good idea to have regular eye tests. It is advisable
to avoid smoky atmospheres and to protect the eyes from direct sunlight.
The eyes also need to be provided with a continuous supply of nutrients.
The eye consists of various structures that focus an image on to the
retina at the back of the eye. Light-sensitive nerve cells on the retina
convert this image into electrical impulses that are carried by the optic
nerve to the brain. The brain controls both eyes that work in conjunction
with each other, aligning themselves onto an object so that a clear image
is formed on each of the retina (1).
AMD causes irreversible blindness in individuals over the age of 65;
it is the leading cause of loss of vision in the Western world. It accounts
for up to 49% of blind registration a year in the UK. AMD is a slow progressive
and painless condition affecting the macula. The macula is the central
part of the retina; light sensitive cells are tightly packed into this
area, allowing fine detail to be processed. AMD occurs when the cells
(the rods and cones) of the macula break down, causing loss of sight in
the central part of the field of vision, but leaving peripheral vision
intact.
There are two types of AMD. The "dry" form is the most common form of
the disease and accounts for 80% of cases. It results from the accumulation
of waste products from within the retina. The "wet" form is much less
common, but accounts for more cases of severe central vision loss. This
type of AMD is brought about by haemorrhaging blood vessels beneath the
retina, with scarring under the retinal-pigmented epithelium.
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Antioxidant
Nutrients
Eyes are particularly susceptible to damage by "free radicals" because
they are exposed to light, have a high consumption of oxygen molecules,
and contain many polyunsaturated fatty acids. Vitamins C, E and Zinc are
particularly beneficial in the health of the eyes.
Vitamin C is essential for protection against damage caused by
oxidative stress (2).
Vitamins C and E have been shown to reduce the risk of AMD due
to their antioxidant activity. Higher blood concentrations of vitamin
E were significantly protective against AMD (3).
Vitamin E is the major chain-breaking antioxidant of cellular
membranes. It is a most effective scavenger of free radicals and is predominant
in human retina and plasma.
Zinc is the most abundant trace element in the human eye. It is
involved in the production of super oxide dismutase (SOD), the antioxidant
enzyme, and in the regulation of catalase activity and is shown to stabilise
membrane lipids against oxidation (2).
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Eye Nutrients
Lutein and Zeaxanthin are two of the
most important nutrients in eye health. They are the only two Carotenoids
present in the lens of the eye and are in particularly high concentrations
in the macula. Lutein and zeaxanthin are carotenoid plant compounds. Many
studies have linked lutein and zeaxanthin intake to decreased risk of
AMD. Lutein collects at the macula and is also known as the 'macular pigment'.
It has the ability to filter short wavelengths of light and so reduce
formation of free radicals. Lutein can also stabilise free radicals without
being damaged itself. The content cannot make lutein; it must be obtained
through the diet. The foods richest in lutein and zeaxanthin are dark
green leafy vegetables and fruit, especially broccoli, kale, spinach,
kiwi fruit and peaches. However, because lutein and zeaxanthin are yellow,
their colour may be masked by the green of chlorophyll in many of the
darker green leafy vegetables. Corn and egg yolks are also a source of
lutein. The average European consumption of lutein is approximately 2mg
a day. Marigold flowers may be used to produce lutein commercially.
Vitamin A is essential for vision; it is a vital
component of visual purple, which is needed for vision in dim light. It
is also a very potent antioxidant and is involved in the repair of cells
that have suffered oxidative damage.
Bilberry (Vaccinium myrtillus) extracts
appear to be of benefit to the eyes. Bilberry has antioxidant properties,
and may therefore help to reduce oxidative stress on the collagen structure
in the eye and in the walls of capillaries that transport nutrient-rich
blood in the eyes. Anthocyanosides in bilberry have an affinity for the
visual purple area of the retina responsible for vision and controlling
the adaptation from dark to light and vice versa (4).
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Lifestyle tips
to help maintain healthy eyes
- Wear sunglasses when exposed to sunlight
- Wear hats with a good brim to shade eyes from direct or reflected
sun
- Eat a diet rich in dark green leafy vegetables and flavonoid-rich
fruit such as bilberries, blackberries and cherries rich in carotenoids
and antioxidant vitamins
- If you are concerned about your diet, consider taking a supplement
specially formulated for eye health, a balanced antioxidant or a multinutrient
- Stop smoking
- Limit your dietary intake of saturated and processed fats and cholesterol
- Try to keep your blood pressure down
- Limit your alcohol intake to the recommended allowance a day
- Visit your optician at least every two years for an eye test
Benefits of an 'eye conscious' diet and lifestyle may
well include reduced risk of cancer, heart disease, obesity, premature
a
intake.
Results in a recent study carried out using veterans
with atrophic AMD (5), showed that subjects given lutein showed a 50%
increase in the average macular optical pigment density over 12 months
compared to those in the placebo group.
Research into AMD is ongoing, so it is worth keeping
an eye on what is happening in the studies!
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Risk factors
for AMD
- Age
- Poor Diet
- Smoking
- Obesity
- Diabetes
- Thickened arteries
- Lack of oestrogen (menopausal women)
- Family history
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- Physical inactivity
- High cholesterol
- High blood pressure
- Cardiovascular disease
- Excess alcohol consumption
- Excessive sun exposure
- Light coloured irises
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Cellular damage caused by reactive oxygen intermediates,
or oxidative stress, has been implicated in many disease processes, especially
age related disorders. Reactive oxygen intermediates include free radicals,
hydrogen peroxide and singlet oxygen. They are often the by-products of
oxygen metabolism.
The retina is particularly susceptible to oxidative
stress because of its high consumption of oxygen, its high proportion
of polyunsaturated fatty acids and its exposure to visible light. The
antioxidant vitamins A, C and E protect cells against oxidative Stress
(2).
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References
- "BMA Complete Family Health Encyclopedia", Ed. Dr. T. Smith. 1996.
DK.
- Surv Ophthalmol, 2000, 45:2: 115-133.
- Am J Clin Nutr, 1995, 62: 1448-1416S.
- "The Healing Power of Herbs", M Murray ND. Prima, 1995.
- Richer, S.P., W Stiles, et al. (2002). "The Lutein Antioxidant
Supplementation Trial (LAST)." ARVO 2002.
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