Color Vision

Introduction

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.

The military also has strict color vision standards. The USAFSAM Color Vision Waiver Guide documents fatal transportation accidents due to color vision deficiencies. The Air Force Research Laboratory at Wright Patterson AFB 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 have those deficiencies exacerbate in high G environments. They also concluded that color combinations of objects with similar luminescence should be avoided in displays for high G aircraft.

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 AMAS 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.

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 several different types of tests allowed (refer to AME Guide for most current guidance as acceptable testing is frequently revised) with include computer based testing and pseudoisochromatic plates (figures found within a series of differently shaded dots) that can be used in the AME’s office for airman’s color vision testing.

Computerized Color Vision Tests:

• City Occupational Colour Assessment & Diagnosis
• Rabin Cone Test – Air Force/Army/Navy/Coast Guard Version
• Waggoner Computerized Color Vision Test

The pseudoisochromatic plates include:

• American Optical Company (AOC) 1965 edition plates 1-15
• AOC-HRR, 2nd edition
• Richmond-HRR, 4th edition plates 5-24
• Dvorine, 2nd edition plates 1-15
• Ishihara, Concise 14 plate, 24 plate and 38 plate editions
• Richmond 1983 edition, 1-15 plates.

Acceptable substitute tests* are the:

• Farnsworth lantern (FALANT)
• OPTEC 900 color vision tester
• Keystone orthoscope
• Keystone telebinocular
• OPTEC 2000 Vison Tester (Models 2000 PM, 2000 PAME, 2000 PI) – Must contain the 2000-010 FAR color perception PIP plate
• OPTEC 2500
• Titmus vision tester
• Titmus i400

*Note that this list is updated frequently.  AMAS recommends you contact an AMAS physician for the most up to date information.  Also color vision tests for airmen are not all acceptable for air traffic controllers.

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.”

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 3930.3B Air Traffic Control Specialist Health Program and require color vision testing during the FAA medical exam. If an on-board controller fails this testing, they are referred for the Air Traffic Controller Color Vision test (ATCOV) which is a computer based operational color vision test typically administered in the Regional Flight Surgeon facilities. If an assigned ATC fails the ATCOV, the RFS will determine if it is possible to grant a Special Consideration for the controller which limits them to certain equipment.

Unrestricted Certificates and Letter of Evidence

Historically, the FAA would grant permanent “Letters of Evidence” based on passing one of the less common alternate color vision tests outlined in the Guide to AMEs and listed above. This would excuse the airman for further future color vision testing. Now such testing has to be passed with each subsequent examination. The only way to get a permanent “Letter or Evidence” or to remove a color vision limitation from their medical is for the airman to request a one time opportunity to take an operational color vision test (OCVT) at their local FSDO. 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. For 1st and 2nd Class certification an additional Medical Flight Test is also required as well. NOTE: If a pilot fails testing during this formal process, they will receive 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.

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.

AMAS Assistance

If you have any further questions concerning color vision standards for pilots/controllers, please contact AMAS for a private consultation.