Genes,symptoms,treatment

1. COLOR
BLINDNESS
BY:ROSE JIMSON
MSc Medical Genetics
SUBJECT-Clinical Genetics
Roll No:06

2. What is colour blindness?
● Color blindness occurs when you are unable to see colors in a normal way. It is also known as color deficiency.
Color blindness often happens when someone cannot distinguish between certain colors. This usually happens
between greens and reds, and occasionally blues.
● In the retina, there are two types of cells that detect light. They are called rods and cones. Rods detect only light
and dark and are very sensitive to low light levels. Cone cells detect color and are concentrated near the center of
your vision.
● Affected individuals have trouble distinguishing between some shades of red, yellow, and green.
● Incidence :1 in 12 men, and 1 in 200 women

3. Structure of Eye

5. ● There are three types of cones-
1.L cones-sense long wavelength (red light)
2. M cones-sense medium wavelength (green light)
3. S cones-sense shorter wavelength (blue light)
● Individuals who have all three types of cones working at full capacity are called
trichromats.Likewise, normal vision can be referred to as trichromacy.
● Anomalous trichromacy-one colour is seen weakly
1.Protanomaly( L cone defect)- Red weak
2.Deuteranomaly (M cone defect)- Green weak [common]
3.Tritanomaly( S-cone defect)-Blue weak [rare]
Classification

6. ● Dichromacy-only two of three primary colours are seen.one one is totally dysfunctional or absent
1.Protanopia(no L-cone/no red cone)
2.Deuteranopia(no M-cone/no green cone
3.Tritanopia(no S-cone/no blue cone)
● Monochromacy (achromatopsia)-1 in every 33,000 people. People with monochromacy see no
color at all. For these individuals, the world exists in black and white.its of 2 types-
1.Blue cone monochromacy:In this type of monochromacy, you only have one cone type that
contains working photoreceptor cells,mostly you see grays. Blue cone monochromats also have poor
vision in general, light sensitivity, nystagmus or shaking of the eyes, and near-sightedness.
2.Rod monochromacy:In this condition your retinal rod photoreceptors work but all or most
cones are absent or malfunctioning.Achromats are also likely to suffer from low vision, nystagmus
and light sensitivity.

7. A
● Tetrachromacy-some women actually have a fourth type of light-
absorbing cone.As many as 12% of women may have “super color
vision,” the fourth cone allowing them to see 100 times more colors than
the rest of the population.Blue cone monochromacy is rarer than the
other forms of color vision deficiency
● Blue cone monochromacy is rarer than the other forms of color vision
deficiency and Red-green color vision defects are the most common
form of color vision deficiency. Both affects males more than females
● Blue-yellow color vision defects affect males and females equally.

8. Genes Responsible
● Mutations in the OPN1LW, OPN1MW, and OPN1SW genes cause the forms of color
vision deficiency.
● The OPN1LW, OPN1MW, and OPN1SW genes provide instructions for making the
three opsin pigments in cones
OPN1LW-Long wavelength,located on X chromosome at position Xq28
OPN1MW-Medium wavelength,position Xq28
OPN1SW-Short wavelength, Chromosome 7 ,Position-7q32.1
● Genetic changes involving the OPN1LW or OPN1MW gene cause red-green color
vision defects.These changes lead to an absence of L or M cones or to the production of
abnormal opsin pigments.

9. ● Blue-yellow color vision defects result from mutations in the OPN1SW
gene.Mutations lead to the premature destruction of S cones or the production of
defective S cones,difficult or impossible to detect differences between shades of
blue and green and causing problems with distinguishing dark blue from black.
● Blue cone monochromacy occurs when genetic changes affecting the OPN1LW
and OPN1MW genes prevent both L and M cones from functioning normally.only S
cones are functional, which leads to reduced visual acuity and poor color vision.

10. Acquired color blindness
● Age – A subtle blue-yellow color blindness can develop with age. Quite simply, the lens
becomes less transparent, affecting how much light reaches the cones.
● Alcohol consumption – Reduced color discrimination can be symptom of alcoholism, with blue-
yellow being particularly affected.
● Brain trauma
● Chronic illness such as Alzheimer’s disease, leukemia, Parkinson’s disease
● Environmental chemicals – Even at low levels, carbon disulphide and lead can cause color
blindness.
● Macular degeneration.

11. Symptoms
● The symptoms of color blindness can range from mild to severe.
● Many people have such mild symptoms that they are unaware that they have a color deficiency.
● Parents may only notice a problem with a child when he is learning his colors.
The symptoms include:
● trouble seeing colors and the brightness of colors in the usual way;
● inability to tell the difference between shades of the same or similar colors. This happens most
with red and green, or blue and yellow.

12. Inheritance Pattern
● X-linked recessive pattern.
● The OPN1LW and OPN1MW genes are located on the X chromosome.
● Blue-yellow color vision defects are inherited in an autosomal dominant pattern

17. Treatment
● Ishihara test plate test is used for the detection

18. ● Colour filter or contact lens can be used to enhance the brightness of
some colours.
● For acquired color blindness, once the cause has been established and
treated,the vision may be restored back to normal

19. Reference
● https://my.clevelandclinic.org/health/diseases/11604-color-blindness
● https://medlineplus.gov/genetics/condition/color-vision-deficiency/#synonyms
● https://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/
● https://www.slideshare.net/qaisersethi9/colour-blindness-ppt-by-meera-qaiser
● https://www.colorlitelens.com/ishihara-test

20. THANK YOU