Optometry Weekly
Color Vision Deficiency
Steven Chang
Pre-optometry
UCLA Class of 2013
Color blindness, or more properly termed,
color vision deficiency, can be a misleading
term. There is no actual blindness involved;
rather the afflicted person has a color
deficiency that prevents them from
distinguishing between colors. Color vision
deficiency occurs predominately in males
because it is an X linked recessive condition.
Approximately 10% of all males are
affected.
Color vision deficiency can either be
acquired or inherited. Acquired color vision
deficiency can occur with aging, ocular
injury, as a result of a medication side effect,
or as a result of some other eye diseases
such as glaucoma or macular degeneration.
There are three different types of inherited
color blindness: monochromacy,
dichromacy, and anomalous trichromacy. In
order to briefly understand the inherited
causes, we will need to discuss the areas of
the eye that is not functioning.
Monochromacy (Figure 2) is caused
when two or three of the cone
pigments are defective. It is also
known as total color blindness.
Dichromacy occurs when one of the
three cone pigments are missing or
defective. The red-green (Figure 3),
blue-yellow color vision deficiency
are categorized as dichromatic
vision. Trichromacy results from an
alteration of spectral sensitivity.
Figure 2
Monochromatic Vision
Figure 3
Dichromatic Red
Green
The main way a patient can be diagnosed
with color vision deficiency is with an
Ishihara colorblind test (Figure 4). It
consists of a series of numbers that are
composed of spots. The background spots
and the spots of the number are different
colors, but a color vision deficient person
would not be able to distinguish between the
two, resulting in failure to distinguish the
number.
Figure 4 Ishihara Test
The retina consists of rod and cone cells.
Cones are responsible for color vision, and
there are three different types of cone cells.
(Figure 1) Each type responds to different
wavelengths, but are commonly referred to
as blue, green, and red cones.
There are currently no treatments for color
blindness though there are specialty tinted
contact lenses that can be prescribed to help
people distinguish between colors more
easily.
Figure 1 Cone Cell Types
“UCLA Ishihara”
Made by Michael Tran
Figure 1: http://www.achromatopsia.info/storage/Cones-Diagram.jpg?__SQUARESPACE_CACHEVERSION=1267499526399
Figure 2: http://printperceive.files.wordpress.com/2011/10/monochromacy.png
Figure 3: http://en.wikipedia.org/wiki/File:Rainbow_Protanopia.svg
Figure 4: http://www.thehindu.com/multimedia/dynamic/00004/ColourBlindness_4671f.jpg
Figure 5: Made by Michael Tran