Color Vision Defects - Color Blindness Introduction A color vision defect causes a person to see colors differently than most people. Color vision defects are sometimes called color blindness. There are three main kinds of color vision defects. Red-green color vision defects are the most common. The other major types are blue-yellow color vision defects and true color blindness, which is a complete absence of color vision. True color blindness is rare. This reference summary discusses the causes, symptoms and treatment of color vision defects. It reviews the different types of poor color vision and includes tips for successfully managing the condition. Anatomy Our eyes are very sophisticated organs. They collect light and focus it on the back of the eye, allowing us to see. The cornea is the front, transparent part of the eye. It allows light to enter the eye. Light hits the iris, which is the colored part of the eye. The opening in the middle of the iris is called the pupil. The iris controls the amount of light that enters the eye by changing the size of the pupil. Cornea Iris Lens As light passes through the pupil, it goes through a clear lens. Like the lens of a camera, the lens of the eye focuses light onto the back of the eye. Retina The back of the eye is called the retina. The retina changes light signals into electric signals. There are two main types of cells in the retina: cones and rods. 1
The electric signals are sent through the optic nerve to the brain, which translates the signals into the images we see, including color. Being able to see all of the colors in the light spectrum depends on your eyes ability to distinguish between the primary colors. The primary colors are yellow, red, and blue. These colors are known as primary colors because different combinations of these three colors allow us to see the whole color spectrum. The retina of the eye has color sensitive cells called cones. Chemicals in the cones allow you to distinguish colors. These chemicals also send information through your optic nerve to your brain, which forms the colored image. If your cones lack any of the light-sensitive chemicals, you may only be able to see two of the three primary colors. Color Vision Defects Most people see the world in color. They enjoy looking at a lush green lawn or a red rose in full bloom. But some people have a color vision defect. They see these colors differently than most people. When people say that they are color blind, they usually mean that they have a color vision defect. There are several types of color vision defects. Some people with color vision defect cannot see or tell the difference between certain colors. For instance, some people cannot tell the difference between the color green and the color red. Other people with color vision defect may have problems seeing a combination of colors. The most severe type of color vision defect is when people can t see any color and see only shades of gray. This is true color blindness and is very rare. It is also called achromatopsia. In most cases, poor color vision is a genetic trait. People inherit the condition from a parent. Men have an increased risk of being born with poor color vision. 2
Symptoms It is possible to have a color vision defect and not know it. The condition usually goes untreated until a confusing situation presents itself. For example, a person may not know they have poor color vision until they have trouble telling the difference between the colors in a traffic light. People with a color vision defect may have trouble distinguishing: Different shades of green and red Different shades of yellow and blue Any colors at all The defects may be mild, moderate or severe. A person with poor color vision may not be able to tell the difference between the colors of the rainbow. If you think that you or a loved one has a color vision defect, talk to your healthcare provider. An eye doctor can perform a test to check for color insensitivity. Causes There are a number of conditions that can cause poor color vision. The following reviews the different causes of color vision defects. Color vision defects may be caused by genetic defects. Often these defects are hereditary, meaning that they were passed on by a parent. Men tend to pass the gene on to their children. Some women possess genes that counteract color vision defects. A person can inherit mild, moderate or severe degrees of poor color vision. The severity of the color vision defect will not change if the cause is inherited. Green-red color deficiency is the most common color vision defect. Fewer than 1 in 10,000 people worldwide will inherit a yellow-blue color deficiency. Achromatopsia is even rarer. Fewer than 1 in 30,000 people will inherit color blindness in which they see only shades of gray. 3
Some medical conditions can cause poor color vision, including: Alzheimer s disease Chronic alcoholism Diabetes Glaucoma Leukemia Macular degeneration Parkinson s disease Sickle cell anemia If a medical condition is the cause of a color vision defect, one eye may be more affected than the other. Poor color vision may get better if the disease that is causing it can be treated. Certain medications can also cause a color vision defect. These medications include drugs used to treat: Anxiety disorders Erectile dysfunction Heart problems High blood pressure Infections Psychological disorders Exposure to certain chemicals can cause a loss of color vision. Carbon disulfide and some fertilizers are known to cause color vision defects. People who regularly work with these chemicals may experience color loss that is too subtle for them to notice. They could benefit from regular eye exams. Your age can also be a cause of poor color vision. As you grow older, your ability to see colors deteriorates slowly. If you suspect that you or a loved one has poor color vision, see an eye doctor for testing. There is no treatment for inherited color vision defects. However, if the cause is a medical illness, treating that illness may improve color vision. 4
Diagnosis If you have trouble distinguishing between certain colors, you should schedule an appointment with your eye doctor. Your eye doctor can test to see if you have a color deficiency. This test is often very quick and easy. Your healthcare provider will likely use a book with several multicolored dot-pattern tests to test your color vision. This test is simple and accurate. If you do not have a color vision deficiency, you will be able to see the numbers and shapes that are hidden within the dot patterns. If you do have a color vision deficiency, you will have difficulty seeing some of the patterns within the dots. If you are severely color-deficient, you might not see anything at all. Prepare for your visit by answering the following questions: When did you first notice trouble seeing certain colors? Do you have any medical disorders? Does a blood-relative have poor color vision? Are you taking any medicines or supplements? Treatment Currently, there is no medical treatment for most types of color vision defects. The only treatable color vision defects are the ones caused by certain medications or medical diseases. Color vision may improve after these conditions are treated. People with poor color vision may benefit from wearing a colored filter over their eyeglasses or a colored contact lens. These items may enhance a person s ability to perceive differences between certain colors. However, they will not improve a person s ability to see the actual colors. Despite the lack of a cure, many people with inherited color defects continue to lead successful lives. They have found ways to work around their condition. 5
One way that people work around their poor color vision is by memorizing the order of colored objects. This allows people to do things like drive a car. By memorizing the order of colors in a traffic light, people with color vision defects can know when to go, yield, or stop. Another way that people work around their poor color vision is by labeling colored items. This helps them do things like organize their clothes by matching colors. They need help knowing which colors go with each other, but once they ve labeled their clothes they can organize their outfits independently. Summary There are three main kinds of color vision defects. Red-green color vision defects are the most common. The other major types are blue-yellow color vision defects and a complete absence of color vision, which is rare. In most cases, poor color vision is a genetic trait. People inherit the condition from a parent. Men have an increased risk of being born with poor color vision. There is no cure for an inherited color vision defect, but many people learn how to work around their condition. Certain medications and some eye diseases also can cause color vision defects. If a medical condition is the cause, one eye may be more affected than the other. Poor color vision may get better if the disease that is causing it can be treated. If you suspect that you or a loved one has a color vision defect, see an eye doctor for testing. Your healthcare provider can easily test your eyes for a color vision defect. 6