THE C TEST
FOR TRITAN CONTRAST
VIEW ONLINE OR DOWNLOAD PDF
To ensure accurate colour reproduction a calibrated medical grade monitor is required. When consumer level electronic devices are used please be aware that results may differ between devices and that the published normal values for the printed version of the test may not apply. High levels of luminance are essential in older subjects with a nuclear lens opacity. The test is not formatted for hand held devices since they are not large enough to provide the correct stimulus geometry.
Before printing a copy of the pdf please be aware that the colour values in the pdf cannot be reproduced in CMYK colour space, which is what an office printer uses. The commercially available print copy of this test was printed on paper with selected whiteness using printers that use extra inks, including light cyan, light magenta, and light grey, as well as the four CMYK inks. Specialised printing firms will be able to print the pdf in ‘RGB colour space’ because the colour calibration is included.
Littlewood R & Hyde F. The “C test” for tritan discrimination. Color research and application 2018;43(1):58-64.
Littlewood R. Normal Tritan Discrimination in Amblyopia Suggests Preservation of Koniocellular Function. International Journal of Ophthalmology & Visual Science 2018;3(3):43-46
The test is monocular. The observer should be instructed to move fixation around the foreground circle until the gap is encountered and then indicate the gap by naming the corresponding letter or pointing, but not touching, the screen (or page.)
The observer should NOT be instructed to look at the centre of the target or to identify and name a shape.
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