The eye?s ability to perceive color is determined by the sensitivity of "cones" in the back of the retina which distinguish different wavelengths of light. There are three types of cones: red, green and blue. These three types of cones work by combining the three primary color, much like a video projector. Wavelengths of light in the visible spectrum progress from the shorter violet colors, through the intermediate blue, green and yellow frequencies to the longer orange and red wavelengths. Not all individuals are born with the ability to perceive differences in color for wavelengths of light. Individuals with substandard color vision detection ability are termed color deficient. Men are ten times more susceptible to color vision deficiencies than women are (8% vs.0.8%).
Color Vision Issues in Aviation
The aviation environment has some phases which require reliance on the ability to detect differences in color for adequate performance. Some of these environments include night flying with the requirement to distinguish red and green position locating lights on aircraft, LED readouts on the instrumentation and warning lights in the cockpit. Additionally, both day and night flight require the ability to distinguish airport tower beacons and lighting from hazardous towers and other obstructions to flight. In the absence of radio communications, the ability to distinguish colored light gun signals from air traffic control tower is necessary for the safe movement of aircraft around that airport. For these reasons, the FAA requires color vision standards to be documented on each FAA medical application. Aviators unable to pass the FAA mandated tests may have restrictions placed on their medical certificate. See Item 52, Color Vision, in the Guide to Aviation Medical Examiners.
The military also has strict color vision standards. The USAFSAM Color Vision Waiver Guide below documents fatal transportation accidents due to color vision deficiencies. The Air Force Research Laboratory at Wright Patterson AFB recently conducted research on the effect of high G exposure on color vision. The reports concluded that the small part of the aviation population with color vision deficiencies will exacerbate those deficiencies in high G environments. They also concluded that color combinations of objects with similar luminescence should be avoided in displays for high G aircraft. These reports were noted in the November 1999 newsletter of the Aerospace Human Factors Association.
Causes of Color Vision Deficiencies
Most cases of color deficiency are inherited, and therefore, determined at birth. Rarely, disease conditions can lead to deteriorations in the ability to detect certain colors. Additionally, some medications can lead to disturbances in color vision, such as Viagra and some cardiac medications. Some antibiotics, malaria preventing drugs, diuretics and barbiturates may also alter color vision. Finally, laser "hits" on the retina may place pilots at risk for acquired loss of color vision.
Because the gene for color vision is found on the X chromosome, color deficiencies are more frequently found in men than in women. Color vision deficiencies are a genetically recessive trait, meaning that if at least one gene for color vision is normal, the individual will have normal color vision. Because men have a single X chromosome and women have two X chromosomes, men are much more likely to be color deficient that women. About 8% of Caucasian males carry such a trait. Contrary to popular belief, most of these individuals are not "color blind", rather their perception of color varies from normal individuals. These individual might be called "color weak". Individuals with normal vision may simulate these altered color perceptions by looking through colored glasses, which is why sunglasses should be a neutral color. (See the VFS article on Optimum Vision and Eye Protection). An extremely rare condition called "monochomatism" leaves an individual with the absence of color sensation. Monochromats view colors similar to the perception from a black and white television.
Certain diseases are associated with color vision deficiencies. These include inflammation of the optic nerve, glaucoma, cataracts, multiple sclerosis, central serous retinopathy, cataracts and toxicity from drugs or poisons. Yellowing of the lens of the eye with age may also alter color perception. This is nature's form of the "Blue Blocker" sunglasses, which are not recommended for pilots. (See the Sunglasses Selection part of the VFS article on Optimum Vision and Eye Protection)
Types of Color Vision Deficiencies
There are two basic types of color deficiency. Those who are "color weak" are called trichromats, as they have cones in the retina to see all three primary colors. Trichromats simply have a relatively fewer number of cones for one type of color. They usually can pass the FAA color light gun test, even if they have not met standards on other types of color vision testing done in a clinical setting.
An individual with the second type of color deficiency is called a "dichromat". These individuals have a complete absence of cones perceiving one of the primary colors. Dichromats make up about 2% of the male population. There are three types of dichromats: protanopes, deuteranopes and tritanopes. Protanopes have an absence or deficiency in red receptor cones, and thus are red-green deficient. Deutroanopes carry a deficiency of green receptors and are also red-green deficient. Both of these types note problems with the aviation signal gun, VASI lights and aircraft position lights. Tritanopes have a deficiency in blue receptor cones and have difficulty with blue-yellow distinctions. All dichromats are at risk for temporary monochromatic vision if looking through tinted lenses or glass.
Diagnosis of Color Vision Deficiency
The diagnosis of color deficiency is based on the inability to reach a passing score on one of a number of color vision tests. These tests may require the ability to perceive an number within a circle of dots of varying shades of dots or a test as basic as naming a color projected from a lamp. Color vision testing is subject to error if improper lighting is used or the examiner gives incorrect instructions. The FAA standards list seven different types of pseudoisochromatic plates (figures found within a series of differently shaded dots) for airman?s color vision testing.
The FAA also lists acceptable substitute tests for color vision testing. The pseudoisochromatic plates include:
American Optical Company (AOC) 1965 edition
AOC-HRR second edition
Richmond-HRR fourth edition
Dvorine second edition
Ishihara concise 14 plate, 24 plate and 38 plate editions
Titmus II vision tester (Model Nos. TII and TIIS) - Possibly no longer acceptable as of Nov 2010
Titmus 2 vision tester (Models T2A and T2S
Cambridge Colour Test
Colour assessment and Diagnosis Test (CAD)
Cone Specific Contrast Test (CSCT).
The military uses pseudoisochromatic plates and the Farnsworth lantern, although the November 1999 revision of USAF aviator standards (para A7.10, page 167) dropped the FALANT as an acceptable color vision test. The Farnsworth lantern closely approximates the aviation light signal gun test.
FAA Color Vision Standards
To meet FAA standards for color vision and hold an unrestricted medical certificate, each applicant must correctly name a certain number of presentations from one of the above-listed tests correctly. The number of correct answers required varies for each test given. Because color vision is generally an inherited condition, it is unlikely that an individual who has failed a properly administered color vision test will subsequently pass on the same test. Many borderline color deficient individuals who are unable to pass the pseudoisochromatic plates have successfully passed the Farnsworth lantern test.
The FAA Guide for Aviation Medical Examiners states that "if an applicant fails to meet the color vision standard as interpreted above, but is otherwise qualified, the examiner may issue a medical certificate bearing the limitation: "NOT VALID FOR NIGHT FLYING OR BY COLOR SIGNAL CONTROL." See Item 52, Color Vision, in the Guide to Aviation Medical Examiners.
Because of events such as NTSB findings in the crash and destruction of a B-727 in Tallahassee, Florida on July 26, 2002 related a contributing cause to deficient color vision in the flying pilot, the FAA reconsidered it's color vision policies for airmen in the Summer of 2008. The list of acceptable and alternate color vision tests for pilot medical certification have not changed, but there are new processes for "operational color testing" of those who fail the routine screen in the AME office. Those changes are summarized later in this article.
For air traffic controllers (ATCS) and ATCS applicants the FAA requires ?normal color vision.? People, generally men, have different degrees of color vision deficiency. It is the degree of deficiency that determines whether one of the tests can be passed. Only a very rare person is truly ?color blind.? If an applicant can pass the FAA color vision test administered, even if slightly color deficient, they would meet standards and would be qualified. If they can not pass the test, they would not be qualified.
The FAA ATC medical standards are found at FAA Order 3930-3A Air Traffic Control Specialist Health Program. The color vision standards for new hires are found at appendix 1, paragraph 1.a.(4). For retention refer to that same appendix paragraph 1.A. (3). It states that an applicant and retained controller must have ?normal color vision?.
However, the prior MGL regarding color vision in controllers specifically states that "on-board FAA ATCS's will no longer be tested periodically for color perception unless there is a history suggesting a change in color perception, unless the ATCS's work performance suggests deficiencies in color perception, unless such testing is deemed necessary as part of a special evaluation of another condition, or unless the ATCS applies for an airman medical certificate." One example of when testing would be indicated is when a controller moves to new equipment and reports to their management that they are not able to see colors sufficiently.
If for various reasons an ATCS is required to re-test their color vision, the prior internal FAA policy for ATCS's who fail the Dvorine test (standard color vision screen with circles containing numbers) was to offer reevaluation with a series of 3 tests, "The Civil Aeromedical Institute (CAMI) Practical Color Perception Test for Air Traffic Control," which reportedly correlates with on-the job performance in the terminal and center operations. Those tests were only administered by FAA Regional Flight Surgeons and are summarized below:
1. Dvorine Pseudoisochromatic Plates - repeat this screening test under standardized conditions allowing no more than 2 errors. If passed, no further testing was required.
2. Aviation Lights Test - modified Farnsworth lantern with test procedure and scoring also modified according to CAMI specifications. Passing requires no more than 1 error.
3. Flight Progress Strips Test - test of the ability of a person based on identification of the black and red flight data strips used in ARTCC's. Passing requires no more than 1 error.
This policy is no longer utilized. In the Fall of 2008 the FAA began to administer the ATCOV which is a computer based operational color vision test for presumably for new applicants and those on board controllers who may fail the tradition pseudoisochromic plates. There is also a CAD test which is still in the experimental stages, but isn't used for pass/fail determination. The ATCOV and CAD are typically administered in the Regional Flight Surgeon facilities. At the time of this writing, it appears that the former tiered system of finding an ATCS qualified for a certain position (e.g. TRACON or CENTER only) will no longer be applicable. Either an ATCS is able to pass the operational test, or they are no longer qualified.
Color Vision -
The Guide to Aviation Medical Examiners goes on to explain how an applicant who has fails the screening test in the AME office might obtain a "waiver". The Guide states "an applicant who holds a medical certificate bearing a color vision limitation may request a signal light test. This request should be in writing and should be directed to the AMCD or RFS. If the applicant passes the signal light test, the FAA will issue a medical certificate without the color vision limitation and provide the applicant with a 'letter of 'evidence'. The signal light test may be given anytime during training."
Unfortunately for the airman with borderline color vision, the opportunities to perform a medical flight test or signal light test are restricted to one, or possibly two, opportunities. The correct interpretation of these tests are left to the FAA pilot inspector. Failure of a signal light test generally results in a permanent restriction on an airman's medical certificate prohibiting night flying and flight by color signal control.
Unrestricted Certificates and Letter of Evidence
For the airman who is uncertain about his or her ability to pass a color vision test, in the past it was far less risky to attempt to pass an alternate color vision test from an eye specialist or aviation medical examiner with acceptable alternates tests rather than seek an operational evaluation with a FSDO. However since the Summer of 2008, the FAA will no longer grant permanent "Letters of Evidence" based simply on passing one of the less common color vision tests outlined in the Guide to AMEs. If you are able to pass one of the less common tests, you will continue to have to pass it at each future medical and thus are viewed as having normal color vision. Virtual Flight Surgeons has located several civilian examiners who can perform tests such as the Farnsworth lantern test. As stated above, an airman who can pass one of the alternative tests and present appropriate documentation to the FAA will be issued an unrestricted medical certificate, but must pass this testing with each future medical.
For those who do not want to take this testing with each exam, the FAA will still allow the "Letter of Evidence" as noted previously and if the new guidance if followed as described in this paragraph. The new procedures for administering the operational color vision tests (OCVT) is outlined in the FAA Flight Standards Guide 8900.1 Vol 5. All pilots seeking to remove color vision restrictions or to obtain a "Letter of Evidence"must request a letter of authorization from AMCD or the RFS to take the testing. For all classes an OCVT is administered which consists of an aeronautical chart interpretation and a signal light test (see link above for specifics of both tests). For 1st and 2nd Class certification an additional Medical Flight Test is also required as described in the link above as well. Figure 5-153A summarizes the process.NOTE: If a pilot fails testing during this formal process, they will recieve a permanent restriction on their medical and are no longer eligible to take alternate testing. At this time, prior "Letters of Evidence" issued before the policy change will remain in effect.
Unacceptable Treatments and Tests for Color Vision
The FAA will not allow the use of an X-chrom contact lens as a means for correcting color deficiencies. The X-chrom lens technique uses a rose colored contact lens in one eye, which results in a "luster" of the color that is typically confused by the pilot and increases the ability of the color deficient pilot to distinguish colors. The FAA specifically prohibits this practice in aviators and controllers.
The recently (November 99) FDA approved ColorMax glasses are also used to enhance color discrimination in color weak individuals. The glasses were featured in the January 4, 2000 USA Today (page 8D). These glasses essentially use color reflecting coatings to alter color perception and enhance discrimination in weak color frequencies. Because other colors may be altered as well, and the deficiency is not completely corrected, the FAA has not approved these glasses for color deficient pilots or controllers.
Yarn tests using strings of different color yarn are not acceptable tests for color vision in pilots.
If you have any further questions concerning color vision standards for pilots/controllers or need assistance in obtaining a color vision "Letter of Evidence", please contact Virtual Flight Surgeons for a private consultation.