Color Deficiency

Have you ever wondered if you or your spouse or perhaps one of your children is color blind? Perhaps their wardrobe choice for the day clashes and just doesn’t work, yet they think it looks great. When most people think of color blindness they think about red-green color blindness which is genetic. About 8% of men and 0.5% of women are born with this color vision deficiency. These are a result of “sex-linked” X chromosomes. This recessive hereditary trait is located on the X chromosome and since men have one X and one Y chromosome, it will be expressed if they have it on their X chromosome. Since women have two X chromosomes, they may be a carrier if only one X chromosome has this trait or they may also have this color vision deficiency if both their X chromosomes have this trait.

Most color perception problems are more accurately referred to as a ‘color deficiency’ rather than as ‘color blind’. The reason for this is that there may be shades of color deficiency. There is an actual test that can determine to what degree a person may be color deficient. Genetic color deficiencies are generally associated with the colors red and green. Reduced sensitivities to the color red are termed Protan whereas the term Deutan refers to reduced sensitivities to green. People with either of these deficiencies will confuse the colors of red and green which will appear similar to them and both of these are genetically inherited. Not all color deficiencies are genetic. In fact, one type, called Tritan, is a blue-yellow deficiency which is an acquired color deficiency and may actually be more common than the genetic types.

Acquired color deficiencies can result from over 300 diseases besides common drugs and substances that can affect the light pathway from the eyes to the brain. The most common examples include diabetes, glaucoma, macular degeneration and long term drug use such as Plaquenil which is used to treat malaria, rheumatoid arthritis and lupus. So how is this clinically useful? Well, by testing for color vision we are testing another aspect of how the eye functions. In this way a Tritan (blue-yellow) color defect can be detected and its severity quantified. This may contribute in the clinical decision making process, for example, in determining when to refer for cataract surgery or when to begin glaucoma treatment. In a study conducted in 2009, it was shown that in people who have ocular hypertension or high eye pressures (but not yet glaucoma), a color deficiency defect would show up before a visual field defect which is a strong predictive factor for the future development of glaucoma. However, those people who had ocular hypertension who did not have a blue-yellow color defect tended to not develop visual field defects1.

Most printed color vision tests do not test for acquired color deficiencies. Rather they are designed to assess genetic red-green deficiencies and only have a screening capability. This is what we have traditionally used in our office. We have recently added a computerized color vision testing system that allows us to detect acquired color vision defects in individuals who could benefit by its use.

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