If you are testing colour vision, ensure that the patient is not wearing a colour-enhancing appliance, such as X-Chrom or Chromagen lenses. In some instances it may be difficult to differentiate these lenses from other, cosmetic tints being worn either as spectacles or contact lenses. Most occupational requirements do not permit the use of such lenses to enable the candidate to pass a colour vision test. If a colour vision test is passed with the use of such an appliance, you should note this on the report form.
Types of colour vision tests
The most common tests for assessing colour vision are the Ishihara plates, City University Test and Farnsworth D-15. However, in many places standards require a Holmes-Wright or Giles-Archer lantern test for colour vision. Neither of these devices have been manufactured for a number of years and very few still remain in working order.
The Clinical Aviation Marine (CAM) lantern test represents a modern alternative to these tests and has been calibrated to give similar results. The CAM lantern may be used in place of the above lanterns where appropriate. The CAM lantern is manufactured by Evans Instruments Ltd and comes with instructions to simulate the results of the older lantern tests.
|Protan defects: abnormalities of the red-sensitive photopigment||Deutan defects: abnormalities of the green-sensitive photopigment||Tritan defects: abnormalities of the blue-sensitive photopigment|
Rare for inherited
Common for acquired
|Anomalous trichromatism||Protanomalous trichromatism||Deuteranomalous trichromatism
Source: Health and Safety Executive
An in-depth guide on colour vision requirements, for occupational health providers and employers, can be found on the Health and Safety Executive website. Alternatively, get in touch with a member of our clinical and regulatory team for advice.