TP 13312

•	Foreword
•	Section 1
•	Section 2
•	Neurology
•	Cardiovascular
•	Diabetes
•	Asthma
•	Other Policies
•	Contacts
•	Alternate Formats

Appendix 2

Colour Vision

In the retina there are two groups of photosensitive cells, the rods and the cones. The cones, concentrated in the central retina, are colour sensitive. They contain three different pigments. One is sensitive to red, another to green and a third to blue. Congenital colour deficiencies are caused either by the absence of one of the pigments or by an alteration in the pigment which leads to distortion of colours. People lacking or deficient in the red pigment are known as Protans, the green pigment Deutans and the blue pigment Tritans. The latter problem is unimportant and unusual.

Normal people are trichromats. Those who have only two pigments are dichromats and, according to the missing pigment, are referred to as protanopes, deuteranopes and tritanopes. There are also groups of trichromats whose pigments, although present, are anomalous. According to the pigment therefore they are protanomalous, deuteranomalous or tritanomalous (trichromats). Approximately 8.5% of the male population and 0.4% of the female population have colour vision defects. About 4.6% of all males are deuteranomalous trichromats and the other 3.4% are evenly distributed amongst the protanomalous trichromats, deuteranopes and protanopes with a frequency of about 1% each.

Pseudoisochromatic plate tests differentiate between people with normal colour vision and those with defective colour vision of types which might interfere with aviation safety. These plates should be viewed by the applicant in natural daylight. The applicant should not be allowed to wear sunglasses or “XChrom” lenses. Each plate should be held approximately 75 cm. in front of the applicant with the plate perpendicular to the visual line. A delay of up to three seconds is allowed for the answer to each plate and it is permissible to repeat a plate if the patient has a negative response. If two responses are given, the second should be recorded. The plates should be given in a random order so they cannot be memorized. The number of acceptable incorrect responses to each type of plate is shown below. Colour vision testing should be carried out from time to time as it also varies in eye diseases and may be an
early method of detecting such problems.

Applicants who fail the plates may be tested with a colour vision lantern. Anumber of these are available in each region and information is available through the RAMO’s office. The Farnsworth D-15 Hue test is also acceptable.

Note: The colour lantern test is not acceptable for initial air traffic controller applicants, who must pass the plates or a Farnsworth D-15 Hue test.