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Issue 84
Age Related Macular Degeneration
The Eye
The structure of the eye is extremely complex and it has evolved in such a way
that each of its components use metabolic pathways specific to their needs.
Each of these components has its own specific job to do and all of them need
to be working properly for the eye to function. The eye has been ingeniously
designed for its purpose of converting reflected light into an image that is
initially up-side down before the brain corrects it. This correction is essential
for us to see long distances as the eye only contains one lens. If the eye contained
two lenses, this correction would not be necessary. This can be explained by
the invention of the telescope. If one were to hold up a magnifying glass at
arms length and tried to view a tree or building on the horizon through it,
the image would be upside down. It was only when another lens was placed in
front of the first lens that people could see extremely long distances in great
detail with the image the right way up!
Through the evolutionary process, nature decided that it was an advantage for
Humans to be able to see long distances to detect potential predators. In this
respect, the health of the eyes was of vital importance for survival alone,
as any injury to the eyes would have rendered us helpless. However, in modern
society, we are fortunate that we no longer have to use our eyes to protect
us from attack from wild animals! Our eyes still enable us to detect danger,
but they also allow us to see all the wonders of nature and the millions of
different colours that accompany it. They also allow us to interact with other
people, express our feelings, read this article and maintain our posture and
balance (as anyone who has tried standing on one leg and closing their eyes
will tell you!).
When we are awake our eyes are constantly being bombarded by light reflected
from hundreds of different objects. Therefore, the eyes work tirelessly during
the day and, as with any machine that is required to work for this duration,
they need a constant supply of fuel.
Fuel for the eye comes in the form of vitamins, minerals and phytonutrients
and these are equired on a daily basis or the function of the eye may become
impaired. One of the most important nutrients for eye health belong to a family
of compounds called carotenoids which include beta-carotene, alpha carotene,
zeaxanthin and lutein and all of these compounds are capable of vitamin A activity.
They can be found in many fruits and vegetables and are used by plants as protection
from UV radiation from the sun.
However, if these nutrients are lacking from the diet, the eye will not function
as effectively and problems with the eyesight can occur. A simple test can be
done to assess whether vitamin A may be lacking from your diet. This would involve
sitting in a brightly lit room and then turning the lights off. The time it
takes for your eyes to adjust will be an indicator of vitamin A status. The
longer the time taken to adjust, the more vitamin A is needed in the diet.
Age Related Macular Degeneration
The efficiency of most bodily functions declines with age and the eyes are
no exception and there are a number of eye conditions that are more common in
the elderly such as cataracts and age related macular degeneration.
Age related macular degeneration (AMD) is a condition which, if left untreated,
can eventually result in blindness. The macular is located at the back of the
eye and enables us to see objects directly in front of us. Therefore, if this
section of the eye was to become damaged then one of the principle symptoms
is loss of central vision. The main cause of this condition is a disturbance
in the blood flow to the eye resulting in an inadequate supply of nutrients.
AMD can occur in two forms called 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 break and leak blood and fluid and
therefore damage to the macula, and loss of central vision, can occur rapidly.
Due to this sudden onset of vision loss, this form of AMD is considered the
more severe. It is for this reason that the early symptoms of wet AMD is taken
seriously, which usually occur in the form of straight lines appearing curved
and irregular. If this is experienced then a detailed eye examination should
follow.
Dry AMD is considered less severe as this form occurs gradually. The light-sensitive
cells (called rods and cones) in the macula break down slowly causing a gradual
blurring of central vision in the affected eye, as opposed to the rapid loss
of vision caused by wet AMD. Symptoms of dry AMD include a need for more light
when reading and it may become more difficult to recognize familiar faces.
Although this condition is primarily associated with old age, there are some
nutritional ways to help delay the onset of the disease. As mentioned above
the eye needs a constant supply of nutrients and many scientific studies have
been conducted which show that two particular carotenoids called lutein and
zeaxanthin are particularly effective for AMD. One particular study found those
consuming 6mg of lutein per day had decreased their risk of developing AMD by
57%. Other studies have shown that out of the 15 carotenoids found in the human
blood stream, only lutein and zeaxanthin are concentrated in the macula, where
they act as free radical scavengers and help protect the eye.
However, there are other nutrients that are equally as important for AMD which
include vitamins A, C and E and zinc. These nutrients have also been shown to
accumulate in the eye and offer protection. Although a dietary deficiency of
these nutrients will increase the risk of obtaining this disease, there are
also lifestyle factors which may predispose someone to the condition. Those
with a family history of AMD should be particularly cautious as should those
who are obese, have high blood pressure and have a history of cardiovascular
disease. Smoking may also increase the risk as this has been shown to deplete
the levels of antioxidants in the body. Prolonged exposure to bright sunlight
is also a risk factor for AMD as UV light has been shown to cause damage to
the retina and macula.
It is therefore, vital that we look after our eyes to help prevent such conditions
occurring, particularly as more and more of us are sitting in front of TV and
computer screens. Our eyes, along with all of our vital organs have to last
for a long time which means they should be looked after properly and not be
taken for granted.
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