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Colour vision

Considerations

The prompt and accurate recognition of colours is an integral part of safe aviation, increasingly so as colour-coded Electronic Flight Instruments Systems (EFIS) displays are becoming the norm. The advent of colour radar screens has rendered the interpretation of weather phenomena much easier.

The information showing on an EFIS is said to be redundant because it is readable even for someone with no colour perception. However faultless rapid data acquisition is important. Without adequate colour perception there is potential to confuse information, i.e. which beacon label relates to which pointer on the Horizontal Situation Indicator (HSI).

Colour coded approach, runway and taxi lights as well as gate parking aids involve multiple colours discrimination. The use of visual signals for clearances (red, green and white) by Air Traffic Controllers has become largely obsolete. Thus functional testing with those lights has become mainly irrelevant.

A US study demonstrated that mild colour deficient persons performed well for correctly and efficiently recognizing PAPI lights and coloured cockpit display symbology. However moderate and severely colour vision deficient persons fell far outside the range of normal response time and accuracy.

Colour vision deficiency affects around 8% of males and 0.5 to 1% of females.

Commonest types of colour vision deficiency in males

  • Protanomaly (1.0%): Reduced sensitivity to red lights.
  • Extreme protanomaly (0.2%): Reduced sensitivity for red lights, reduced colour discrimination for red, yellow and green.
  • Protanopia (1.0%): Reduced sensitivity for red lights; confusion of red, yellow and green.
  • Deuteranomaly (4.5%): Colour matches different from those made by normals.
  • Extreme Deuteranomaly (0.5%): Reduced colour discrimination for red, yellow and green.
  • Deuteranopia (1.5%): Confusion of red, yellow and green.

Acquired colour vision deficiency

Although much less common than congenital defects, acquired colour vision defects do occur. These may affect one eye more than the other and may be progressive. Blue colour perception is generally most affected. The Ishihara plates do not screen well for such deficiencies.

Causes include:

  1. Retinal degeneration and pigmentary retinopathies;
  2. Chorioretinitis from any cause including macular lesions;
  3. Optic neuropathy from any cause including advanced glaucoma;
  4. Drug toxicity affecting the macula or the optic nerve;
  5. Intra ocular lenses;
  6. Use of coloured contact lenses, etc.

For this reason colour vision tests should be repeated in case of any suspected eye disease and also following refractive surgery.

Examination procedure

The ME must conduct a colour perception test on all first applicants, using the Ishihara printed plates in accordance with the GD Examination Procedure [PDF 1.6 MB] - section 11.

The use of X-Chrom, ChromaGen, Colorview, or similar lenses to improve colour vision discrimination are not acceptable.

The ME should conduct the test even if the applicant is to be referred to an optometrist or ophthalmologist.

The ME should be aware that an applicant with a known or suspected colour vision defect may have learned the plates which must be presented in random order.

If there is any doubt regarding the interpretation of colour vision tests, the ME should promptly seek advice from the CAA.

Disposition

  • A Class 1, 2 or 3 applicant who incorrectly identified Ishihara plates as specified in the Examination Procedures GD [PDF 1.6 MB], schedule 1, section 11, must be considered as having a colour vision deficiency.
  • A Class 1 or Class 2 applicant with colour vison deficiency may be assessed as having a condition that is not of aeromedical significance if the certificate is endorsed in accordance with the Colour Vision GD [PDF 798 KB] – section 11
  • A Class 1 or Class 2 applicant with colour vision deficiency who has undergone and failed further testing as outlined in the Colour Vision GD, section 10, may be assessed as having a condition that is not of aeromedical significance if the certificate is endorsed in accordance with the Colour Vision GD [PDF 798 KB] – section 11
  • A Class 1 or Class 2 applicant with colour vison deficiency who has undergone and passed further testing, as outlined in the Colour Vision GD, section 10, may be assessed as having a condition that is not of aeromedical significance and issued an unrestricted certificate in accordance with the Colour Vision GD [PDF 798 KB] – section 11
  • A Class 1 or Class 2 applicant with colour vison deficiency who has undergone and failed further testing may be assessed as having a condition that is not of aeromedical significance if the applicant has undergone and passed the relevant components of an Operational Colour Vision Assessment certificate and is endorsed in accordance with the Colour Vision GD [PDF 798 KB] – section 12

The following organisations can provide further testing:

  • School of Optometry, University of Auckland (CAD test and Optec 900 Lantern, an accepted Farnsworth Lantern equivalent);
  • Mr Frank Snell, optometrist in Auckland (Holmes-Wright type A Lantern);
  • Mr Peter Grimmer, Wellington, (Holmes-Wright type B Lantern);
  • Most optometrists: Farnsworth D15.
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