Color Blindness

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color vision deficiency

Kayla Jones

M. Barreuther

Biology

11/19/2012

                 Color vision deficiency

“What color is this?” is the most annoying question you can ask your colorblind friend. Color blindness, contrary to popular belief, does not mean that you are devoid from seeing all color. Color blindness is actually the incorrect term for the actual problem of color vision deficiency. Color vision deficiency is the inability or lessened ability to see color or detect color differences. ‘Blindness’ is not the correct term for this condition because one is not technically blind. A good percent of the population has this deficiency and the majority of those affected are males. Among people aged 40 or older, 3.6 million are visually impaired. 8% of all men are color blind compared to the .05% of women in the United States that are. Color blindness is not only hereditary, although that is the most common cause, but this inability to see colors can be caused by head/brain injuries, damage to the optic nerve or physical damage to the eye. No matter what the cause, color vision deficiency is a very life-impacting problem throughout the United States, caused by the make-up of the sex-linked X chromosome.

                Inheritance and causes

        A typical human retina contains two light cells: cones and rods. Rod cells are used for night time or low light situations and cones are for daylight or normal light. Cones have three different types and these all differ by the pigments that are picked up when light hits them. S, M, and L are the types of cones (short wavelength, medium wavelength and long wavelengths respectively) but they are more commonly known as red, blue and green. The genes involved in color vision are located in the X sex chromosome, which causes the problems to often happen in males, who have one X chromosome. Women have two X chromosomes, which lessons her chance of losing color vision. If a woman inherits one X chromosome and one that carries the mutation, she will only be classified as a carrier. She needs to have both X chromosomes that carry the mutation, which is pretty rare. One normal X chromosome cancels out a mutated one. Moreover, if a female is colorblind, all of her sons will be colorblind and her daughters have a 50% chance of being either colorblind or not.

        Inherited colorblindness comes in three different types: monochromacy, dichromacy, and anomalous trichromacy. It can be congenital, which means from birth, or it can develop in childhood. The mutation of the gene is unstable and can develop worse throughout the person’s life, sometimes even to the point of complete blindness (in extremely rare cases).

 Monochromacy is the rare disability to be able to see any color and therefore also known as ‘total color blindness’. Two of all three cones must be malfunctioning or missing for this to happen. Dichromacy is when one of the three cones is absent or malfunctioning, reducing the color into two dimensions. This may cause red to appear very dark or the complete absence of blue color receptors. The final type, anomalous trichromacy is when the sensitivity of one of the cones is skewed. This often harms the ability to determine colors apart from each other. The most common sensitivity that is thrown off is the distinction between red and green hues and in some more uncommon cases, green/yellow and blue. These three types can be caused by different cones being missing, and two people might be monochromatic due to having a malfunction in their rods instead of cones.