Do You Have Color-Vision Deficiency?
Do You Have Color-Vision Deficiency?
“When I get dressed, my wife checks that the colors I choose match,” says Rodney. “At breakfast she selects a piece of fruit for me because I can’t see if the fruit is ripe. At work I can’t always see where to click on the computer screen, since items are often distinguished by color. When I’m driving, red and green traffic lights appear the same to me, so I observe whether the illuminated light is on top or on the bottom. Horizontal lights, however, can present a problem.”
RODNEY has color-vision deficiency, also called color deficiency or color blindness. He inherited a genetic flaw that causes a defect in the retina—the light-sensitive inner lining of the eyes. Rodney shares this condition with about 1 of every 12 males of European ancestry and about 1 of every 200 females. * Like the vast majority of sufferers, Rodney can see different colors—he does not see only black and white. But some colors do not look the same to him as they do to people with normal vision.
In the human eye, the retina normally contains three kinds of cone-shaped color-sensitive cells. Each kind is tuned to the wavelength of a different primary color of light—blue, green, or red. Light of different wavelengths triggers the corresponding cones, which signal the brain and enable one to perceive colors. * In people with color-vision deficiency, however, the sensitivity of the cones to one or more colors is weak or shifted in wavelength, so that their response to color is altered. Most sufferers have difficulty distinguishing between yellow, green, orange, red, and brown. This defect can make it hard to see green mold on brown bread or on yellow cheese or to distinguish a blue-eyed blonde from a green-eyed redhead. If a person’s red-sensitive cones are very weak, a red rose appears black. Very few sufferers cannot see blue.
Color-Vision Deficiency and Children
Defects in color vision are usually inherited and present at birth, and children with the condition often learn unconsciously to compensate. For instance, even if they cannot see the difference between certain hues, they may perceive differences in contrast and brightness and associate these variations with the names given to the colors. They may also learn to identify objects by surface patterns and textures instead of by color. In fact, many young people remain unaware of their disability throughout childhood.
Because schools often use color-coded teaching tools, especially in the early grades, parents and teachers may mistakenly think that a child has a learning disability when, in fact, he may have a color-vision deficiency. One teacher even punished a five-year-old boy for painting a picture that had pink clouds, green people, and trees with brown leaves. To a child with color-vision deficiency, these colors may seem perfectly normal. For good reason, therefore, some authorities recommend routine color-vision testing in early childhood.
Although there is no known cure for this condition, it neither worsens with age nor increases the risk for other defects in vision. * Still, color-vision deficiency is a disability that can be frustrating. Under God’s Kingdom rule, however, Jesus Christ will remove every trace of imperfection from God-fearing humans. Thus, people who had visual defects of any kind will see Jehovah’s handiwork in all its glory.—Isaiah 35:5; Matthew 15:30, 31; Revelation 21:3, 4.
[Footnotes]
^ par. 3 Color-vision deficiencies can be found in all racial groups, but it is most common among Caucasians.
^ par. 4 Many animals can discern colors, although their color vision differs from ours. Dogs, for example, have only two kinds of cones in their retinas—one for blue and the other for a hue between red and green. Some birds, on the other hand, have four kinds of cones and can detect ultraviolet light, which is beyond the human range.
^ par. 8 Color-vision deficiency can sometimes be caused by disease. If you notice changes in your color vision later in life, you may want to see an eye doctor.
[Box/Diagrams on page 18]
TESTS FOR COLOR-VISION DEFICIENCY
Tests to discover the type and degree of color-vision deficiency that a person has often employ patterns of dots in various hues and shades. The widely used Ishihara test consists of up to 38 different patterns. For example, when viewing one of the test patterns in daylight, a person with normal vision should see the numbers 42 and 74 (at left), while someone having a red-green deficiency—the most common—may see no number at the top and 21 at the bottom. *
If testing reveals a defect, an eye doctor may recommend further tests to determine whether it was inherited or has some other cause.
[Footnote]
^ par. 15 These diagrams are presented only for the purpose of illustration. Diagnostic tests should be performed by a qualified professional.
[Credit Line]
Color test plates on page 18: Reproduced with permission from the Pseudoisochromatic Plate Ishihara Compatible (PIPIC) Color Vision Test 24 Plate Edition by Dr. Terrace L. Waggoner/www.colorvisiontesting.com
[Box on page 19]
WHY MAINLY MALES?
Inherited color deficiencies are carried on the X chromosome. Women have two X chromosomes, while men have one X and one Y. Thus, if a woman inherits a visual defect in an X chromosome, the normal gene in the other chromosome will likely override it, and her vision will be fine. But a man who inherits a defect on his X chromosome has no other X chromosome to fall back on.
[Diagram/Pictures on page 18]
(For fully formatted text, see publication)
HOW WE SEE COLORS
Light from objects passes through the cornea and the lens and is focused on the retina
Cornea
Lens
Retina
The image is inverted but corrected later by the brain
THE OPTIC NERVE carries visual impulses to the brain
THE RETINA contains cone cells and rod cells. Together they give the full range of vision
Rods
Cones
THE CONE CELLS are sensitive to red, green, or blue light
Red
Green
Blue
[Pictures]
Normal vision
With a color-vision deficiency