I am a 33-year-old male. When I underwent a medical test one year back the eye specialist told me that I have color blindness. Is it curable with medicines or diet? Please let me know.
Color blindness is the most common of a number of inherited conditions which are passed on by sex-linked recessive inheritance. “Sex-linked” means that the gene causing the condition is located on one of the chromosomes that determine the sex of a person, usually the X chromosome, and recessive means that it will not be expressed if it is opposed by a normal gene in the other chromosome of the pair. To understand this, let me review a little genetics.
All animals including humans have their genes arranged on chromosomes, and each chromosome is paired, that is, our cells contain two copies of the same chromosome. The members of the pair may however contain different genes. If the gene on one member of the pair exerts its effect regardless of the same gene on the other member of the pair, it is said to be dominant, and the other gene is said to be recessive. If both genes are active in a cell, then there may be no dominance, or partial dominance. If a person inherits two recessive genes, one from each parent, then that person will show the action of those genes, which may simply be a physical trait, such as blue eyes, or may be a disease, such as Tay-Sachs disease.
One chromosome pair is different from all the others, the XX or XY pair that determines sex. All women are XX, meaning they received one X chromosome from each parent. All men are XY, meaning that they received an X from their mother, and a Y from their father. Since women have only X chromosomes to contribute to their offspring, the sex of all children is determined by the father’s chromosome, which may be X (the child will be female) or Y (the child will be male). The Y chromosome is much smaller than the X, and carries very a few genes. Therefore genes on the X chromosome from the mother usually are the only ones active in a male child on that chromosome pair, and if the mother’s X chromosome carries the gene for color blindness, which is very common, then her sons may be color blind, since the Y chromosome from their father carries no gene for color vision.
When a woman carrying the gene for color blindness conceives a girl, the child will usually not be color blind, since she will inherit another X gene from her father, and the normal color vision gene on his chromosome will be dominant over the color blindness gene on the mother’s chromosome. (An exception to this occurs when a female carrier of the color blindness gene conceives a daughter by a male who is himself color blind. In this case all his X chromosomes carry the gene for color blindness, and since half her chromosomes also carry the gene, approximately half her daughters will be color blind, as will be half her sons.)
Similar X-linked recessive inheritance is seen in several other conditions, including hemophilia A, which affected the Romanoff line of Russian czars, Duchenne’s muscular dystrophy, G6PD deficiency, and others. In the case of color blindness the genes make it difficult to impossible for the person to distinguish reds from greens and affected men are often unaware of their condition until they are tested, as was the writer of today’s letter, since they have never really appreciated those colors. The degree of color blindness also varies in affected people, with a few completely unable to distinguish red from green, and many more with only partial inability to do so.
There is no treatment for inherited color blindness, and no dietary changes or supplements will affect it. Vitamin A, which is important for the maintenance of vision, particularly night vision, will not help. There are some disturbances of color vision which can be side effects of drugs. Perhaps the best known is the blue vision that can be caused by Viagra, but many other commonly used drugs including barbiturates, digitalis, sulfa drugs and thiazides (common diuretics) may change color vision on occasion; however, none of them will cause true color blindness.