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Farnsworth D15 Dichotomous Color Test Farnsworth Test for Congenital and Acquired color defects. The Farnsworth D-15 contains a reference disc holding notation 10 B 5 4 and fifteen numbered discs which make up an incomplete color circle. The patient arranges the discs and then evaluation of the patients arrangement separates 'normal' color perception from moderate and strong defects in deutan, protan or tritan axis color discrimination. The D-15 is housed in a plexiglass container. the disks are spread out on a table and arranged by the patient. The Farnsworth D-15 test is a subset of the well known Farnsworth 100 Hue Test. It is intended for classification instead of in-depth study of color vision defects. The D-15 and 100 hue tests are correlated. Growing Importance of Color deficiency Screening. In addition to congenital color deficiency screening there is growing evidence that adult acquired color deficiency, especially in yellow and blue perception, can indicate medical toxicity and other problems. Increasingly complex security and medical systems also require verification of all three types of color receptors. How the D-15 test works: The Farnsworth D15 is called 'dichotomous' because it is designed to separate subjects into one of two groups, 1) Strongly color deficient or 2) Mildly color deficient or color normal. This is accomplished by the arrangement of vivid (saturated) colored discs. A perfect score shows normal color perception. A non-perfect score is used to determine a medium or strong color deficiency.