Color blindness is more accurately referred to as color vision deficiency, because it is very rare for individuals to be able to see no color at all, to be truly color blind. Most cases of color blindness occur because of a sex-linked gene located on the X chromosome. The American Optometric Association notes that up to 8 percent of males and 0.5 percent of females are born with some degree of color vision deficiency. Lantern tests for color blindness simulate signal lights and are used most commonly by professions requiring the accurate interpretation of signals, flags or other colored stimuli.
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Daniel Flück, author of Colblindor, a website describing color blindness through color-blind eyes, explains that lantern tests were introduced first by railway companies in the late 1890s. The companies realized that some of their workers could not tell the difference between certain signal lights. One of the first tests of this type was the Williams Lantern Color Sense Test, which was developed in 1899. However, currently in the United States, the Farnsworth Lantern test, also known as the FALANT, is used most commonly. Specifically, the Navy, Marines and Coast Guard use the FALANT to diagnose color blindness, reports Discovery Health.
How Does the Test Work?
The FALANT uses colored signal lights that must be named from a distance. Two lights are shown at the same time, and the color red, green or white must be identified, according to Discovery Health. The lights are darkened with a filter to ensure that the colors cannot be distinguished based on their brightness.
Who Fails the Test?
To pass the test, the subject cannot make any errors. Discovery Health notes that generally, all dichromats, individuals missing one of the three color-sensing cones in the retina, and almost all anomalous trichromats, individuals who have trouble telling green, yellow and red apart, fail. The FALANT is specially designed to pass people with a mild form of color vision deficiency, to permit these individuals entry into the military and other professions, notes Colblindor.
Lantern tests for color blindness directly test the required ability, distinguishing between signal lights, and therefore are very practical. However, they do not reveal very much about the nature, type and severity of the color vision defect, nor do they provide much in the way of clinical information.
Dr. Cole and Dr. Vingrys, from the Department of Optometry at Melbourne University, administered the FALANT to 100 individuals with abnormal color vision and reported in “Documenta Ophthalmologica” that there is a lack of strong correlation between clinical tests, which reveal details of the color vision deficiency, and the recognition of small color lights, presented by the lantern tests. Therefore, clinical color vision tests may not test the same aspect of color vision that is important to the recognition of signal lights. For this reason, lantern tests should be essential for occupational and profession-specific testing of color vision.