THE MIRACLE OF
COLOUR VISION TESTING
Colour vision is a complex topic that cuts across many scientific sub disciplines, not to mention artistic and cultural endeavours. Colours have mysterious psychological effects as well as cultural symbolism. We can measure anomalies of colour perception but we never know what it is like to live in someone else’s head.
We offer a range of colour vision tests including Ishihara, City University, HRR and colourmate pseudoisochromatic plate tests for red / green contrast perception. We also have the C test, the only plate test validated for blue – yellow (tritan) contrast perception.
A routine assessment of colour contrast perception includes the best 16 Ishihara plates, a C test, a D15 colour sorting test, and either a 100 hue or Nietz anomaloscopy test (Rayliegh match), depending on the purpose of the measurement.
An Optec 900 lantern is the modern equivalent of the now obsolete Farnsworth Falant (which went out of production nearly 40 years ago and cannot be factory serviced). This lantern test is required by several transport authorities and the armed services. A different lantern test, called the Holmes Wright, is required for marine navigation.
The Nietz anomaloscope performs a Rayliegh (red / green mixture vs. yellow) match, and is the modern equivalent of a Nagel anomaloscope. It is the best instrument for correctly assigning an axis of confusion and quantitatively measuring the severity of colour confusion along a red / green axis.
A colour vision test may also require an assessment of the optics of the visual pathway, including biomicroscopy, contrast sensitivity testing using sinusoidal waveforms, and retinal assessment, to ensure that any colour vision defect is not the result of a disease or abnormality that requires treatment.
A complete colour assessment is very time consuming and requires a lot of expensive technology, which is why it costs more than a routine clinic visit. If you would like an assessment for personal or occupational reasons you will need to make sure the receptionist books a long consultation to allow enough time to complete all the tests and write a report.
The test results alone do not allow those unfamiliar with the tests to correctly interpret them, so a written report is provided to enable those who are not familiar with the tests to correctly interpret the test results.
The button below will download a pdf copy of an article discussing colour processing – What is colour?
The button below will download a pdf copy of an article describing the correct use of the Ishihara plate test
The button below is a link to an online article about the C test for tritan discrimination
Littlewood R & Hyde F. The “C test” for tritan discrimination. Colour research and application 2018;43(1):58-64
COLOUR PUBLICATION ARCHIVE
Amblyopia involves functional suppression of the parvocellular signal at the lateral geniculate nucleus but the koniocellular signal, as measure by the C test, is preserved. The article below describes the use of the C test in amblyopia
Littlewood R. Normal Tritan Discrimination in Amblyopia Suggests Preservation of Koniocellular Function. International Journal of Ophthalmology & Visual Science 2018;3(3):43-46.
The button below will download a pdf copy of an essay entitled “The history and physiology of human tritan perception.” This discussed the evolution of human colour vision in a narrative style that non scientists may find accessible.
The button below will download a pdf copy of a paper comparing the Ohkuma and Ishihara plate tests
Clinical colour testing for tritan contrast relies on blue / yellow contrast detection by the koniocellular system. The C Test is a spiral bound book with 10 pseudoisochromatic plates. Each plate displays a target with two blue / yellow contrast borders. The difficulty increases from plates 1 to 10.
A C Test score of less than 9 out of 10 is highly suggestive of optic nerve or diffuse retinal disease in the absence of dense cataract. The C test usually alters earlier and than the Ishihara or Snellen acuity tests in optic neuropathies and stays abnormal for longer.
Every Eye Matters
© 2019 All content remains the property of Dr Ross Littlewood without written permission for re-use