Colour Vision Defect

Colour Vision Defect also known as Colour Blindness is the inability to distinguish different colours.

Red-green Colour Blind

Red-green colour blind, sees red and green as the same hue, only being distinguished by the colour's intensity

Blue-yellow Colour Defect (Titan Defect)

People affected by tritan color blindness confuse blue with green and yellow with violet.

Blue Cone Monochromacy

People affected by Blue Cone Monochromacy (BCM) have gene variants in the X-chromosome which damages the retina

Frequency

Red and green colour defect is most the common among the vision defects. About 7 percent of all men and about 0.6 percent of women inherit the condition, but the condition is more common in men, with women only able to be carriers.

Blue and yellow colour defect otherwise known as the tritan defect effects 1 in 10,000 world wide. It effects both men and women equally, but occurs less then the red and green colour defect

Top: normal vision/Bottom: tritan vision

blue cone monochromacy effects 1 in 100,000 world wide, and affects more males then females.

Signs & Symptons

The symptoms of color blindness are often observed by parents when children are young. In other cases, symptoms are so slight, they may not even be noticed. Common symptoms of colour blindness include: Difficulty distinguishing between colours. Inability to see shades or tones of the same colour. Rapid eye movement (in rare cases)

Extra information

Males can have 1 x chromosome and females have 2 x chromosomes.

  • OPN1LW - opsin 1, long wave sensitive. This provides instructions for making an opsin pigment that is more sensitive to light in the yellow/orange part of the spectrum
  • OPN1MW - opsin 1, medium wave sensitive. This provides instruction for making an opsin pigment that is more sensitive to light in the middle. In response to light, the photopigment triggers a series of chemical reactions within the wavelength sensitive. People can have more or one copies in a row on the x chromosome near the OPN1LW
  • OPN1SW - opsin 1, short wave sensitive. This pigment provides instrustions for making an opsin pigment that is more sensitive to the light in the blue/violet part of the visible spectrum

Genetics

Red-green and blue cone monochromacy are inherited in an x-link recessive pattern. The OPN1LW and OPN1MW are located on the x chromosome, which is on one of the two sex chromosomes. Males are affected by the x-linked recessive disorders more frequently the females, because in females a genetic change would have to occur on both copies of the chromosomemto cause disorder.

Blue-yellow colour vision, other wised known as Titan Defect, are inherited in an autosomal dominant pattern, which means one copy of the altered OPN1SW gene in each cell is sufficient enough to cause the condition. In many cases, an affected person inherits the condition from an affected parent.

All of theses opsins can be found in the retina, which is the light-sensitive tissue at the back of the eye. The retina contains two types of light receptor cells, called rods and cones, that transmit visual signals from the eye to the brain. Rods provide vision in low light. Cones provide vision in bright light, including color vision

Testing

Ishihara 38 Plates Test

The often called Ishihara plates were introduced by Dr. Shinobu Ishihara from Japan long time ago. Since then this test is the most well known all around the world.

This test consists of 38 different pseudoisochromatic plates. Each of them hides a number or line behind colourful dots. Based on what you can see and what not, it is possible to check if you are suffering from some form of red-green colour blindness

F-M 100 Hue test

This famous colour vision test—which is based on 88 colored plates and not 100 as the name suggest—was introduced in 1943 by Farnsworth.

The test will show you four batches of 22 mixed coloured plates. What you have to do is to arrange the for rows of plates in a correct order

Colour Arrangement Tests

In 1947 Farnsworth released the D-15 dichotomous test. This is to this day one of the most famous colour vision deficiency test and definitely the most famous colour arrangement test.

You simply have to arrange the given colours in the correct order of colours. If you are suffering from some form of colour blindness, you will arrange them quite differently compared to persons with normal colour vision

RGB Anomaloscope

The RGB Anomaloscope can be used to check if you are suffering from red-green color blindness or not. Unfortunately it is not possible to differentiate between the different forms of red-green color vision deficiency

Prognosis

Prognosis. Colour blindness that is inherited is present in both eyes and remains constant over an individual's entire life. Some cases of acquired colour vision loss are not severe, may appear in only one eye, and last for only a short time. Other cases tend to be progressive, becoming worse with time

Treatment

There is no treatment for inherited colour blindness. If colour blindness is caused by another condition, treating the underlying cause can help

Bibliography

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