Prevalence of red green color vision defects

Prevalence of Red-Green Color Vision Defects among Muslim Males

and Females of Manipur, India

Color blindness

Inability or decreased ability to see color, or perceive color differences, under normal lighting conditions.

Affects a significant percentage of the population.

No actual blindness -- deficiency of color vision

• No treatment

• Nor the cause of any significant disability

• No actual blindness -- fault in the development of one or more sets of retinal cones that perceive color in light and transmit that information to the optic nerve.

• It is a sex-linked condition.

• Perception of color begins with specialized retinal cells containing pigments with different spectral sensitivities, known as cone cells.

• In humans, there are three types of cones sensitive to three different spectra, resulting in trichromatic color vision.

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Anatomy of an Eyeball

6

The Genetics of Color-Blindness

The Retina Contains Two Types of Light-Detecting Cells

Rods – “See in shades of grey”

– Cannot distinguish different wavelengths (colors) of light.

– More sensitive to low light– Used for night-vision

• Cones – “See in colors”

– Three types of cones; differ in which photoreceptor protein (opsin) they make

• L-cones sense long-wavelength (red) light

– Make the long-wavelength opsin protein

• M-cones sense medium-wavelength (green) light

– Make the medium-wavelength opsin protein

• S-cones sense short-

wavelength (blue) light– Make the short-wavelength

opsin protein

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Visible light is small part of electromagnetic spectrum.

700 600 500 400

UVIR

Cone cells in the human eye

Cone type Name Range Peak wavelength

S β 400–500 nm 420–440 nm

M γ 450–630 nm 534–555 nm

L ρ 500–700 nm 564–580 nm

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Red, green and blue cone

sensitivity vs. wavelength

curves

Retinal Cones–Normal Color Vision

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B RG

437 nm 564 nm533 nm

NORMAL CONE SENSITIVITY CURVES(TRICHROMAT)

Color-Vision Genes

• Three kinds of color-vision genes in humans:

"blue" pigment gene on chromosome 7"red" and "green" pigment genes at the tip

of the long arm of the X chromosome-Xq28

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Types of Color Vision Deficiencies

By causeInherited:

•Trichromacy (“three-color vision”)– Normal Color Vision

•Anomalous Trichromacy (“unusual three-color vision”)– See all three primary colors.– One color is seen weakly

• Protanomaly (L-cone defect) red-weak

• Deuteranomaly (M-cone defect) green-weak, by far the most common type of color vision deficiency

• Tritanomaly (S-cone defect) blue-weak

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How Color-Blind People See Things

Defect in L-cone (poor red vision)

Normal

Defect in M-cone (poor green vision)

Defect in S-cone (poor blue vision)

Dichromacy (“two-color vision”)

– See only two of the three primary colors– One type of cone is totally absent or nonfunctional

• Protanopia (L-cone absent)Pure reds cannot be seen, instead appearing black; purple colors cannot be

distinguished from blues; more orange-tinted reds may appear as very dim yellows

• Deuteranopia (M-cone absent)moderately affecting red–green hue discrimination

• Tritanopia (S-cone absent) Blues appear greenish, yellows and oranges appear pinkish, and purple colors

appear deep red

A rainbow of colors as viewed by a person with no color

vision deficiencies

The same rainbow as viewed by a person with protanopia

The same rainbow as viewed by a person with deuteranopia

The same rainbow as viewed by a person with tritanopia

Monochromacy, -- "total color blindness", is the lack of ability to distinguish colors

•Rod Monochromacy (no cones at all) (“no-color vision”)– Sees no colors, only shades of gray.

•Cone monochromacy is a rare total color blindness -result of having more than one type of dichromatic color blindness

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Some Views With and Without Color Vision

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Color Deficiency

Males Females

Protanopia 1% 0.01%

Deuteranopia 1% 0.01%

Protanomaly 1% 0.01%

Deuteranomaly

5% 0.4%

Overall (red-green)

8% 0.5%

Tritanopia 0.008%

0.008%

Tritanomaly Rare Rare

Rod monochromati

sm

Rare Rare

Cone monochromati

sm

Rare Rare

Acquired Causes Damage to the eyes, nerves, brain Some metabolic disorders like • diabetes

• glaucoma

• macular degeneration Chronic illness • Sickle cell anaemia Exposure to industrial toxins Drug over dose such as- digoxin, barbiturates, anti-

tubercular drugs Drug side effects like- Sildenafil (Viagra), Ethambutol,

Chloroquine

By Clinical Appearance

Total or partial. Total color blindness is much less common than partial color blindness.

Partial color blindness

– Red–green

Dichromacy (protanopia and deuteranopia)

Anomalous trichromacy (protanomaly and deuteranomaly)

– Blue–yellow

Dichromacy (tritanopia)

Anomalous trichromacy (tritanomaly)

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How Color-Blind People See Things

What people with normal color vision see.

What a red-green color-blind person sees.

Congenital color vision deficiency (CVD) is an X chromosome-linked recessive, autosomal dominant and very rarely autosomal recessive inherited trait.

Red-Green defects (Protan and Deutan) show the highest prevalence in the general population.

Impaired color vision, in the case of red-green color blindness, is genetically determined by X- linked recessive inheritance and thus occurs in males but is transmitted via female and about 8.0% of all women are its carrier.

X-linked recessive inheritance

Materials and Methods

Populations

• Manipur -- small hilly state

• Situated in the north eastern extreme corner of India.

• Connects the Indian subcontinent to East Asia and South East Asia as a unique narrow passageway

• Shares an international boundary with Myanmar (Burma)

• Isolated from the rest of India, both geographically and economically

• Manipuri Muslims -- 8.32% of the total population -- 2001 census.

• Mostly migrants -- started coming -- middle of the 16th century

• Manipur Muslims -- endogamous population

• Sheikh• Syed• Pathan

• Mughal

• Clan names which in Manipuri are called Yumnak

• About 74 clans are reported in Manipur in the present times

Methods

A cross-sectional, descriptive and analytical study to detect color-blindness -- Ishihara color test

Individuals belonging to both sexes (Male-1352, Female -1302) from the area of Imphal East and Imphal west districts during house to house visit.

Survey was also conducted taking Manipuri students studying in Aligarh Muslim University, Aligarh.

Population groups Muslims with castes •Sheikh

•Syed

•Pathan

•Mughal

Hindu (Meitei)tribal(Naga)Prior informed consent from the individuals, taking into consideration the factors like caste, consanguity, age, religion etc.

Color vision deficiency -- 24-plate Ishihara’s Test of Color Vision

Testing plates -- 75 cm from the person Tilted at right angle to the line of vision Done in a properly lighted place Read the numbers -- test plates 1 to 17 Assessment of the reading of plates 1 to 15 -- normality or

defectiveness of color vision If 13 or more plates are read correctly, the color vision is

regarded as normal. If only 9 or less than 9 plates are read correctly, the color

vision was regarded as red green deficient. The plates 16 and 17 are used to differentiate protan and

deutan types of color vision efficiency.

Plate 1

Both normal and those with all colour vision deficiencies should read the number 12

Plate 2Those with normal colour vision

should read the number 8. Those with red-green colour

vision deficiencies should read the number 3.

Total colour blindness should not be able to read any numeral.

Plate 3Normal vision should read the number 29.

Red-green deficiencies should read the number 70.

Total colour blindness should not read any numeral

Plate 4Normal colour vision should read the number 5.Red-Green colour deficiencies should read the

number 2.Total colour blindness should not be able

toread any numeral.

Plate 5Normal colour vision should read the

number 3.Red-Green deficiencies should read the

number 5.Total colour blindness should not be able

to read any numeral.

Plate 6Normal colour vision should read the number

15.Red-Green deficiencies should read the

number 17.Total colour blindness should not be able to

read any numeral.

Plate 7Normal colour vision should read

the number 74.Red-Green colour deficiencies

should read the number 21.Total colour blindness should not

be able to read any numeral.

Plate 8Normal colour vision should read the number

6.The majority of those with colour vision

deficiencies cannot read this number or will read it incorrectly.


number 45.The majority of those with colour vision deficiencies cannot read this number or

will read it incorrectly.

Plate 10Normal colour vision should read the number 5.

Those with colour vision deficiencies will not read the number or read it incorrectly.


number 7.Those with colour vision deficiencies

will not read this number or read it incorrectly.


number 16.Those with colour vision deficiencies

will not read this number or read it incorrectly.

Plate 13Normal colour vision will read the number

73.Those with colour vision deficiencies should nor be able to read this number or will read it

incorrectly.

Plate 14Normal colour vision and those with total colour blindness should not be

able to read any number.The majority of those with red-green

deficiencies should read the number 5.

Plate 15Normal colour vision and those with total colour blindness should not be

able to read any number.The majority of those with red-green deficiencies should read the number

45.


number 26.In protanopia and strong protanomalia the number 6 is read and in mild protanomalia both numerals are read but the number 6 is

clearer than the number 2.In deuteranopia and strong deuteranomalia

only the number 2 is read and in mild deuteranomalia both the number 2 is clearer

than the number 6.


number 42.In protanopia and strong protanomalia the number 2 is read and in mild protanomalia both numerals are read but the number 2

is clearer than the number 4.In deuteranopia and strong

deuteranomalia only the number 4 is read and in mild deuteranomalia both the

number 4 is clearer than the number 2.

Plate 18The normal should trace along the

purple and red lines between the two X's.

In protanopia and strong protanomalia only the purple line is traced and in mild protanomalia both lines can be traced but the purple line is easier to

follow.In deuteranopia and strong

deuteranomalia only the red line is traced and in mild deuteranomalia both

lines are traced but the red line is easier to follow.

Plate 19The majority of those with red-

green colour blindness can trace the winding line between the two

X's.The majority of those with normal

and total colour blindness are unable to follow the line.

Plate 20Normal will trace the blue-green line

between the two X's. The majority of those with colour vision deficiencies will be unable to follow the line or will follow a line different to the

normal one.

Plate 21Normal will trace the orange line

between the two X's. The majority of those with colour vision deficiencies will be unable to follow the line or will follow a line different to the

normal one.

Plate 22Normal should trace the line

connecting the blue-green and the yellow-green.

Those with red-green deficiencies trace the line

connecting the blue-green and purple.

Those with total colour blindness cannot trace any

line.

Plate 23Normal should trace the line connecting

the purple and the orange between the two X's.

Red-green deficiencies should trace the line connecting the purple and the blue-

green.Total colour blindness and weakness

cannot trace any line.

Plate 24Both normal and those with colour

vision deficiencies can trace the winding line between the two X's.

Genetic Data Analysis

• Phenotypes were recorded for color blindness for each individual

• Allele frequencies were calculated -- Hardy-Weinberg law.

• Level of heterozygosity

Hetrozygosity = 1- ΣHo

Ho -- homozygosity of the allele

Results Face many difficulties in every-day life, some discussed during the survey include •Inability to recognize red and green LED displays on electrical goods•Difficulties in driving vehicles

Regarding health -- difficulties faced in differentiating primary colors•Lack of confidence•Poor social image i.e. a fear that they are not alike to normal vision individuals.

• Males -- denied the military jobs on grounds of color blindness have stopped pursuing further studies

• Very few of well educated families have taken this in a positive way and have started their life in a new way

• General population was mostly unaware of the difficulties that color blindness can cause; besides they have neither undergone any screening test

• Naga tribes -- least prevalence of color blindness in both males and females

• Four Muslim caste and the Meitei population -- higher prevalence of color blindness.

Phenotypic frequency

Allele Frequency

Discussion

• Prevalence of the trait -- muslims is important -- consanguineous marriages -- might result in the birth of children with this disorder

• The overall percentage of color blindness -- 5.28%

• higher percentage -- males than in females

• Females -- carriers – 8.37%

• Meitei male -- highest color blindness prevalence rate of 14.93%

• Syed population (11.48%) belonging to Muslim religion

• Naga population -- the least prevalence rate of 3.75%

• High prevalence rate in Muslims -- higher frequency of consanguineous marriages

• Meitei population -- highest prevalence percentage of 8.16% -- large number of migration by Manipuri people over the past few years, to different parts of India, indirectly leading to increase in the rate of exogamous marriages with non-manipuri populations

• Deuteranomaly cases -- higher percentage

• Overall prevalence rate of Protanomaly, Deuteranomaly, Protanopia, Deuteranopia is 17.14%, 54%, 8.57% and 20% respectively

• Several researchers -- green color receptor is commonly affected more than red or blue color receptors

Early diagnosis -- beneficial for future family planning and lifestyles

Helpful to create awareness among the parents and general public about screening of color vision defects in apparently healthy children

Nonfatal disorder; usually remain unaware of the defect since their vision is otherwise normal.

Important for daily life work such as to recognize the traffic signals during crossing roads or to build career in several professions like- in Military, Pilot, Driver or Chemist etc.

• Congenital color blindness cannot be treated -- non pathologic, incurable, and remain constant throughout life

• Several therapies have been proposed Electrical eye stimulation Iodine injections Large doses of vitamins

• No treatments or surgical procedures to improve the quality of an individual’s chromatic vision.

• Optometrists give colored spectacle lenses or a single red-tint contact lens to be worn over the non-dominant eye. Although this may improve discrimination of some colors, it can make other colors more difficult to distinguish.

• X-chrom contact lens

• Education, screening and prenatal counseling for the disease in these areas could help

Minimizing the occurrence of the disorder Help them to make informed choices and avoid the birth

of children with color blindness

• Moral support from the family and society is required for the healthy development of mental status of the individual suffering from this disorder

• Government should also make certain policies and programmes regarding career choices and jobs for color blind individuals.