deuteranopia , and if a person’s blue
cones are affected, it is known as
tritanomaly or tritanopia. In very
rare cases (roughly one in 33,000), a
person will have no cones at all – a
condition known as achromatopsia
– which means they have no colour
vision and see everything in black,
white and shades of grey.
Most people with red/green
colour blindness will have inherited
the condition from their mother, and
most will be male. This is because
the condition is passed on via genes
on the X chromosome. A woman
has two X chromosomes – she can
have one faulty X chromosome,
and one normal X chromosome,
and the normal X chromosome will
be dominant and she will not have
CVD. However, if she does have
a faulty X chromosome, any male
children she has will have a 50 per
cent chance of inheriting colour
blindness. Men, on the other hand,
have just one X chromosome. If their
single X chromosome is faulty, they
will be colour blind.
CVD involving the colour blue
is far less common than red/green
colour blindness – it accounts for only
five per cent of colour blindness, and
it affects men and women equally, as
it is passed on via a different, non-
sex-linked chromosome. But CVD is
not always genetic. Less commonly,
people can develop it in later life,
either as a result of long-standing
illnesses such as eye disease, multiple
sclerosis, liver problems or diabetes,
or as a result of a trauma or injury to
the head or eyes.
Early years
Like the majority of people with
colour blindness, Tom inherited the
condition. His mum, Paula Lambert,
from Discovery Bay, explains, “My
dad and three of his brothers are
colour blind. I knew it ran in the
family, so I was looking
out for it in Tom from
about the age of
three. I noticed that he was having
trouble identifying colours when he
seemed to grasp other things, like
shapes, pretty easily. When he was
at kindergarten in Mid-Levels, an
optician came round to give the
children routine eye tests, and he
told us that Tom had failed his colour
blindness test. Although testing at
such a young age can be inaccurate,
in Tom’s case they were definitely
right.”
The early years at school can be
some of the hardest for a child with
CVD. Paula remembers picking Tom
up from a different kindergarten one
day, and finding him desperately
upset: he had been made to miss
playtime as he hadn’t finished his
colouring in, a task he never enjoyed.
And leaving aside the frequent
colouring and painting – which a
child may find demoralising and
confidence-sapping if he is constantly
being told he is using the “wrong”
colours – during the pre-reading
years, there is a heavy reliance
on colour coding. Children might
regularly be asked to put the crayons
in the green tub, put the balls in the
yellow bag, or put the books in the
red tray. A child who consistently
struggles with these instructions can
sometimes be seen as uncooperative if
his CVD has not yet been diagnosed.
Surprisingly, most teachers currently
receive no specific training on dealing
with colour blind students.
Moving on up
As a child moves up through
school, the challenges can continue,
especially for those whose CVD is
most severe. In maths lessons, how
can a child count the number of red
cars, or shade his graph red if he can’t
work out what “red” is? In science,
how can he record a litmus result if he
cannot read the colour of the paper,
December 2013
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