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Webvision: Color Perception <br />Cta 199$.(I1 Pi ire z image). <br />Colour vision tests <br />Page 13 of 18 ' ' <br />Confusion lines form the basis of many colour vision tests such as the Farnsworth Panel D-15 and <br />Ishihara Pseudoisochromatic plates. Pseudoisochromatic plate tests are also commonly used in the clinic <br />to screen for colour vision deficiency. Colours are carefully chosen based on the confusion lines. The <br />most commonly used pseudoisochromatic plate in the clinic would be the Ishihara Isochromatic plates <br />(for screening red -green colour vision deficiency) and the Tritan (F-2) plate. <br />Pseudoisochromatic plates are designed in four ways: <br />1. Transformation plates: where a person with normal colour vision sees one figure and a CVD <br />person sees another (figure 21a). <br />2. Vanishing plates: where a person with normal colour vision see the figure while a CVD person <br />will not (figure 21b). <br />3. Hidden -digit plates: where a person with normal colour vision does not see a figure while a CVD <br />will see the figure (figure 22a). <br />4. Diagnostic, plates: designed to be seen by normal subjects with colour vision defectives seeing one <br />number more easily than another (figure 22b). <br />Q +Ox:u. <br />d IP't+�s� <br />a +� p`H z a t �- •� �i � Y.ts"kit t s� �%,'Y t,rw t§� �� � �,#' �,w:�' <br />.27 A <br />$. <br />C5'rr}.,� t;ut F�se+%, t''ip, <br />.»., .. .rtes t..... <br />(a) tb) l)' (b) <br />should sea 3 wWIe z CVD p -mon s:ronld see 5_(b! i he v anishin? <br />matof the Ishiiiaaa. Nor al ahaulci see l3 whafc; a CyI will not <br />Lead the f mires con ecfh . (aFz jpe im�e-I <br />The Ishihara colour vision test is a screening test and the fail criterion for the Ishihara is typically <br />four or more plates. Further colour vision testing will be required to confidently diagnose the type <br />of colour vision defect. Another useful screening plate test is the Farnsworth F-2 plate (Pease, <br />1998). There are many colour vision tests available for screening and for diagnosis of which only <br />a few will be discussed here. The colours of the Panel D-15 are also carefully chosen from the <br />CIE diagram so they are all isoluminant (that is, have the same value) as seen in figure 23. <br />http://www.webvision.med.utah.edu/KallColor.html 6/18/01 <br />