Colorblindness, Partial, Protan Series

Alternative Names

  • CBP
  • Protanopia
  • Red Colorblindness
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WHO-ICD-10 version:2010

Diseases of the eye and adnexa

OMIM Number

303900

Mode of Inheritance

X-linked

Gene Map Locus

Xq28

Description

Red color blindness is a disorder that affects the way an individual perceives color.  The retina detects colors through cone cells.  There are three types of cones in the human eye, each containing a specific photo-pigment that is most sensitive to particular wavelengths of light, i.e. red, blue or green.  In individuals affected with protanopia, there are no working red cone cells.  This results in the patient perceiving red light as black.  In the milder condition of protanomaly, the red cone photo-pigment is abnormal.  Red, orange, and yellow appear greener and colors are not as bright.

The disorder is much more prevalent in men.  It affects one in ten males and only about one in two hundred females.  Prevalence also differs between races, with northern European populations showing a higher incidence of the disease.  The disorder only affects the perception of color and does not affect visual acuity.  However, it can still negatively affect the quality of life in affected individuals.  Children are particularly inconvenienced by the disorder as most educational aids in classrooms are color-coded.  Hence it is important that the condition is properly diagnosed.  Several different tests can be used to diagnose color vision defects.  The Ishihara plate test, for example, uses colored circles which contain a collection of dots in different colors and sizes.  The dots form a shape that while clearly visible to most people, would be difficult to identify for those with color vision defects.  The Farnsworth-Munsell 100 Hue Test is another widely used analysis that measures the ability to discriminate between subtle color changes.  While there is no cure for the disorder, certain contact lenses and glasses may help users perceive colors more accurately. 

Molecular Genetics

The disorder follows an X-linked pattern of inheritance.  In humans, the long-wave-sensitive opsin-1 gene (OPN1LW) encodes the red cone pigment and the medium-wave-sensitive opsin-1 gene (OPN1MW) encodes the green cone pigment.  While there is a single red pigment gene, green pigment genes vary in number among individuals.  The red pigment gene and multiple green pigment genes are arranged in a head-to-tail tandem array.  Nonhomologous pairing and unequal crossing-over between these genes results in a hybrid 5-prime red--3-prime green fusion gene causing protanopia or protanomaly.  Color vision defects can also be a result of mutations in the OPN1LW gene. 

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Abdelmoneam (2011) studied the prevalence of color vision deficiencies (CVD) in Saudi women.  He recruited 7467 women of Arab origin from all five regions of the country.  The participants ranged in age from 13 to 68 years.  They were all healthy with no ocular pathology.  The subjects were tested for CVD using the Ishihara pseudoisochromatic plate test and the D-15 test.  Subjects found to have CVD were further evaluated with the FM 100 hue test.  The screening revealed 26 women who had color vision defects.  The prevalence of CVD among Saudi females was thus found to be 0.35%, a rate that is much lower than other races.  There was also no significant difference in the prevalence of CVD between different regions of the country.  Of the 26 women, 10 subjects were found to have a protan color defect. 

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