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Screening Tests to Diagnose Color Blindness

Diagnosing Color Blindness We often joke about being color blind, but in its truest sense it is a serious condition. Color deficiency, in which a person has difficulty distinguishing between colors, is a fairly common condition, though much more so in men. It is estimated that one in ten men and one in a hundred women have some form of color blindness. Total color blindness, where the person sees only in shades of gray, is fortunately very rare.

What is color deficiency?
The retina, which captures an image much like the film in a camera, is made up of layers of tissue and within them are photoreceptors called rods and cones. There are three types of cones responsible for color vision, and a deficiency will produce confusion between the colors. The most common forms of color blindness involve the red and/or green cones and cause difficulty differentiating between reds and greens. Color deficiency is usually hereditary and congenital but can also be the result of an accident or exposure to certain chemicals.

There are two types of tests associated with color vision problem. The first is used simply to detect a color vision problem, while more detailed, quantitative tests are also available to ascertain the type and severity of the color blindness.

Diagnosing color blindness
The most commonly used test for color blindness is the Ishihara Color Vision Test. It is named after the Japanese ophthalmologist who devised the procedure in 1917 and first published a paper on it. The Ishihara Color Vision Test is a booklet of pages each with a circular pattern made up of colored dots in various colors, sizes and degrees of brightness. The colored dots are arranged so that a person with normal color vision will clearly see a number within the array of dots in a different color. A color blind person will either see a different number, or no number at all. The full test has 38 plates, but generally only 14 or 24 plates are used. The test is usually taken in normal room lighting with the patient wearing their normal eyeglasses, if needed. Note: this test is unsuitable for young children who can't accurately identify numbers.

Measuring color blindness
For a more detailed analysis of color blindness, a quantitative test is needed, the most common of which is the Farnsworth-Munsell 100 Hue Test. Four trays with many small colored disks of varying hues are given to the patient, who must arrange the disks in a gradually ascending scale of color. The test should be administered in a room or booth with natural daylight (or the closest simulation possible) for maximum accuracy. To score the exam, the administrator compares the patient's layout to a key, using numbers on the bottom of each disc; the closer the match, the more accurate the person's color vision.

A alternative version of the test, the Farnsworth-Munsell D15 Test, is similar but has just 15 colored disks. It may be used for color vision screening purposes but, like the Ishihara Color Vision Test, cannot quantify a personís color blindness.

Who should be screened for color blindness?
Most people are color blind from birth and therefore are unaware of their color vision deficiency. There is no treatment for color blindness although in some cases tinted contact lenses improve the differential between different colors.

Anyone pursuing a profession which requires color accuracy should be screened for color blindness. This includes would-be electricians, commercial artists, designers, technicians, police officers, pilots and those interested in certain military careers, as safety and job performance can depend heavily upon accurate color perception.

What about online color blindness tests?
There are many color blind tests available online which are a variation of the Ishihara screening test. However, colors will vary depending on your specific monitor settings and exact color representation is essential for the accuracy of the test, thus screening tests are not considered accurate. Those who need to be screened for the disorder should see an eye care specialist to have a full color blindness test administered.

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