Sunday, March 09, 2008/10:09 PM
Colour Blindness
Colour blindness may be a hereditary condition or caused by disease of the optic nerve or retina, and it is much more common in men than in women.
Patients with a colour vision defect caused by disease usually have trouble discriminating blues and yellows. Inherited colour blindness is most common, affects both eyes, and does not worsen over time. This type is found in about 8% of males and 0.4% of females. These colour problems are linked to the X chromosome and are almost always passed from a mother to her son. Colour blindness may be partial (affecting only some colours), or complete (affecting all colours). Complete colour blindness is very rare. Those who are completely colour blind often have other serious eye problems as well.
Step 2: We now add a digit pattern which is defined by yellow/blue variation only.
Step 3: Now we add another digit pattern which is defined by red/green variation and is easier to see than the pattern defined by yellow/blue variation.
Step 4: Finally we add all three components: the random brightness pattern, the yellow/blue pattern, and the red/green pattern. Observers with red/green deficiency will not be able to see the red/green pattern and base their response on the yellow/blue pattern only.
Patients with a colour vision defect caused by disease usually have trouble discriminating blues and yellows. Inherited colour blindness is most common, affects both eyes, and does not worsen over time. This type is found in about 8% of males and 0.4% of females. These colour problems are linked to the X chromosome and are almost always passed from a mother to her son. Colour blindness may be partial (affecting only some colours), or complete (affecting all colours). Complete colour blindness is very rare. Those who are completely colour blind often have other serious eye problems as well.
Photoreceptors called cones allow us to appreciate colour. These are concentrated in the very center of the retina and contain three photosensitive pigments: red, green and blue. People with normal cones and light sensitive pigment are able to see all the different colors and subtle mixtures of them by using cones sensitive to one of three wavelengths of light - red, green, and blue. Those with defective colour vision have a deficiency or absence in one or more of these pigments. Those with normal colour vision are referred to as trichromats. People with a deficiency in one of the pigments are called anomalous trichromats (the most common type of color vision problem). A dichromat has a complete absence in one cone pigment.
Signs and Symptoms
The symptoms of colour blindness are dependent on several factors, such as whether the problem is congenital, acquired, partial, or complete.
Difficulty distinguishing reds and greens (most common)
Difficulty distinguishing blues and greens (less common)
The symptoms of more serious inherited colour vision problems and some types acquired problems may include:
Objects appear as various shades of gray (this occurs with complete colour blindness and is very rare)
Reduced vision
Detection and Diagnosis
Colour vision deficiency is most commonly detected with special coloured charts called the Ishihara Test Plates. On each plate is a number composed of coloured dots. While holding the chart under good lighting, the patient is asked to identify the number. Once the colour defect is identified, more detailed colour vision tests may be performed.
How do things look?
Many people think anyone labeled as "colour blind" only sees black and white -- like watching a black and white movie or television. This is a big misconception and not true. It is extremely rare to be totally colour blind (monochromasy - complete absence of any color sensation). There are many different types and degrees of colour blindness - more correctly called colour deficiencies.
How color vision testing works
Step 1: A color vision test pattern for testing red/green deficiency starts from a random pattern of gray level dots.
Step 2: We now add a digit pattern which is defined by yellow/blue variation only. This pattern can be detected by any observer which is able to do yellow/blue discrimination. Since most people with red/green deficiency will be able to do yellow/blue discrimination they will be able to see the digit 5 in this test pattern.
Step 3: Now we add another digit pattern which is defined by red/green variation and is easier to see than the pattern defined by yellow/blue variation. Here is the pattern composed of the random brightness pattern and the red/green pattern:
Step 4: Finally we add all three components: the random brightness pattern, the yellow/blue pattern, and the red/green pattern. Observers with red/green deficiency will not be able to see the red/green pattern and base their response on the yellow/blue pattern only. Normal observers will see both the yellow/blue and the red/green pattern. Since the red/green pattern is stronger than the yellow/blue pattern the normal subject will base his or her judgment on the red/green pattern and see the digit 6.
Treatment
There is no treatment or cure for colour blindness. Those with mild color deficiencies learn to associate colours with certain objects and are usually able to identify colour as everyone else. However, they are unable to appreciate colour in the same way as those with normal colour vision.
SO, APPRECIATE YOUR EYES!
There is no treatment or cure for colour blindness. Those with mild color deficiencies learn to associate colours with certain objects and are usually able to identify colour as everyone else. However, they are unable to appreciate colour in the same way as those with normal colour vision.
SO, APPRECIATE YOUR EYES!
Without them, and without the normal functioning of your rods, you wouldn't be able to see nature's most colourful phenomena --
A RAINBOW (:
♥Love, Nic.