Fróðskaparrit - 01.01.1979, Síða 62

70
Anthropological and Genetic Studies of the Faroese
Colour Vision Deficiency
There are a number of forms of colour vision deficiency
and because of the sex-linked mode of inheritance of the more
common forms they are considerably more frequent in males
than in females. In the Faroes 148 males and 126 females were
examined. There were a few older and younger individuals
but the majority of the sample were 14 to 19 year olds. Al!
subjects were initially tested with Ishihara pseudo-isochromatic
charts. These so-called ‘colour confusion’ charts are composed
of dots of different colours in which the colour vision deficient
person sees a different number or pattern to that seen by a
normal person. Subjects who made 5 or more errors on this
test were given a second more rigorous test using a Davidson
and Hemmendinger colour rule. In this instrument two mov-
able scales of gradually changing colour (at constant bright-
ness) appear through an aperture. The colour on the two scales
matches only when they are in certain positions relative to
each other. The colour vision deficient person is detected by his
or her inability to restrict the number of positions at which
the scales appear to match. The two tests together enable a
diagnosis of the type and severity of the disorder. Colour
vision deficiency was detected in a total of 12 Faroese, 11
males (7.4 %>) and 1 female (0.79 %). The value of 7.4 % is
intermediate between values of 5.2 % and 10.1 % for Orca-
dian and Norwegian males respectively (Boyce et al., 1973;
Schiotz, 1922). However owing to the small sample size this
figure must be viewed with caution. Further investigation is
required to determine whether the apparently high frequency
of colour vision deficiency in males from the Northern and
Central regions relative to the Southern group reflects a ge-
nuine difference or is a chance effect due to the small size.
Discussion
The Icelandic Landnámabók or book of the settlement de-
scribes the origins of about 5 °/o of the early settlers of lce-
land. It indicates that over 60 % of these were from Norway