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Caterina Ripamonti, Sarah Kalwarowsky, Marko Nardini; A Universal Colour Discrimination Test suitable for observers with low vision. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3536. doi: https://doi.org/.
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Most of the popular colour vision tests (e.g. Ishihara, FM 100 Hue Test) were originally developed to screen and classify dichromats. As these individuals enjoy relatively normal visual acuity, the ‘good-visual-acuity’ requirement to perform these tests has been neglected. As a consequence, individuals affected by low vision may be wrongly diagnosed with a colour vision deficiency on the basis of their failure to perform these tests. In some patient groups with low vision, measuring chromatic discrimination may be useful for monitoring disease progression and evaluating the success of new treatments. For this reason, we have developed a Universal Colour Discrimination Test (UCDT), which is suitable also for individuals with visual acuity worse than 1.0 logMAR.
The test consists of circles of random luminance presented on a computer screen. A small sub-set of circles delineates a large 5-degree square that varies in saturation and hue. Observers indicated whether the coloured square appeared on the left or on the right. A staircase procedure measured the minimum saturation required for each observer to discriminate the square from the achromatic background. The task was easy to perform, even by 7-year-old observers. Participants were labelled as Normal or Affected according to their performance to additional colour vision tests included in the protocol.
We describe colour discrimination using three indices, which are derived by fitting the observers’ thresholds with an ellipse: the length of the major axis (m.a.), its angle (phi), and the axial ratio (r). We found that Normal r was approximately equal to 1 and generally agreed with Normal r obtained with the Cambridge Colour Test (CCT). Normal m.a. showed no particular orientation, and was about 1 log unit shorter than Affected m.a. Affected phi was consistent (when the comparison was possible) with the observer’s performance at other tests. More importantly, our test was able to measure colour discrimination in all Affected observers, including those who, due to their low visual acuity had been unable to perform the conventional colour vision tests, including the CCT.
The UCDT can accurately measure colour discrimination even in observers with low vision. This result has important clinical implications, as it allows to determine chromatic discrimination baselines and monitor their changes in patients undergoing clinical treatments.
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